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Comparing JSON-XS/README (file contents):
Revision 1.12 by root, Wed Jun 6 18:17:13 2007 UTC vs.
Revision 1.26 by root, Tue Jun 3 06:43:45 2008 UTC

…		…
1	NAME	1	NAME
2	JSON::XS - JSON serialising/deserialising, done correctly and fast	2	JSON::XS - JSON serialising/deserialising, done correctly and fast
3		3
		4	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
		5	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
		6
4	SYNOPSIS	7	SYNOPSIS
5	use JSON::XS;	8	use JSON::XS;
6		9
7	# exported functions, they croak on error	10	# exported functions, they croak on error
8	# and expect/generate UTF-8	11	# and expect/generate UTF-8
9		12
10	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	13	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
11	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	14	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
12
13	# objToJson and jsonToObj aliases to to_json and from_json
14	# are exported for compatibility to the JSON module,
15	# but should not be used in new code.
16		15
17	# OO-interface	16	# OO-interface
18		17
19	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	18	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
20	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	19	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
21	$perl_scalar = $coder->decode ($unicode_json_text);	20	$perl_scalar = $coder->decode ($unicode_json_text);
		21
		22	# Note that JSON version 2.0 and above will automatically use JSON::XS
		23	# if available, at virtually no speed overhead either, so you should
		24	# be able to just:
		25
		26	use JSON;
		27
		28	# and do the same things, except that you have a pure-perl fallback now.
22		29
23	DESCRIPTION	30	DESCRIPTION
24	This module converts Perl data structures to JSON and vice versa. Its	31	This module converts Perl data structures to JSON and vice versa. Its
25	primary goal is to be correct and its secondary goal is to be fast.	32	primary goal is to be correct and its secondary goal is to be fast.
26	To reach the latter goal it was written in C.	33	To reach the latter goal it was written in C.
		34
		35	Beginning with version 2.0 of the JSON module, when both JSON and
		36	JSON::XS are installed, then JSON will fall back on JSON::XS (this can
		37	be overridden) with no overhead due to emulation (by inheriting
		38	constructor and methods). If JSON::XS is not available, it will fall
		39	back to the compatible JSON::PP module as backend, so using JSON instead
		40	of JSON::XS gives you a portable JSON API that can be fast when you need
		41	and doesn't require a C compiler when that is a problem.
27		42
28	As this is the n-th-something JSON module on CPAN, what was the reason	43	As this is the n-th-something JSON module on CPAN, what was the reason
29	to write yet another JSON module? While it seems there are many JSON	44	to write yet another JSON module? While it seems there are many JSON
30	modules, none of them correctly handle all corner cases, and in most	45	modules, none of them correctly handle all corner cases, and in most
31	cases their maintainers are unresponsive, gone missing, or not listening	46	cases their maintainers are unresponsive, gone missing, or not listening
35		50
36	See MAPPING, below, on how JSON::XS maps perl values to JSON values and	51	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
37	vice versa.	52	vice versa.
38		53
39	FEATURES	54	FEATURES
40	* correct unicode handling	55	* correct Unicode handling
		56
41	This module knows how to handle Unicode, and even documents how and	57	This module knows how to handle Unicode, documents how and when it
42	when it does so.	58	does so, and even documents what "correct" means.
43		59
44	* round-trip integrity	60	* round-trip integrity
		61
45	When you serialise a perl data structure using only datatypes	62	When you serialise a perl data structure using only data types
46	supported by JSON, the deserialised data structure is identical on	63	supported by JSON, the deserialised data structure is identical on
47	the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"	64	the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
48	just because it looks like a number).	65	just because it looks like a number). There minor are exceptions
		66	to this, read the MAPPING section below to learn about those.
49		67
50	* strict checking of JSON correctness	68	* strict checking of JSON correctness
		69
51	There is no guessing, no generating of illegal JSON texts by	70	There is no guessing, no generating of illegal JSON texts by
52	default, and only JSON is accepted as input by default (the latter	71	default, and only JSON is accepted as input by default (the latter
53	is a security feature).	72	is a security feature).
54		73
55	* fast	74	* fast
56	Compared to other JSON modules, this module compares favourably in
57	terms of speed, too.
58		75
		76	Compared to other JSON modules and other serialisers such as
		77	Storable, this module usually compares favourably in terms of speed,
		78	too.
		79
59	* simple to use	80	* simple to use
		81
60	This module has both a simple functional interface as well as an OO	82	This module has both a simple functional interface as well as an
61	interface.	83	object oriented interface interface.
62		84
63	* reasonably versatile output formats	85	* reasonably versatile output formats
		86
64	You can choose between the most compact guarenteed single-line	87	You can choose between the most compact guaranteed-single-line
65	format possible (nice for simple line-based protocols), a pure-ascii	88	format possible (nice for simple line-based protocols), a pure-ASCII
66	format (for when your transport is not 8-bit clean, still supports	89	format (for when your transport is not 8-bit clean, still supports
67	the whole unicode range), or a pretty-printed format (for when you	90	the whole Unicode range), or a pretty-printed format (for when you
68	want to read that stuff). Or you can combine those features in	91	want to read that stuff). Or you can combine those features in
69	whatever way you like.	92	whatever way you like.
70		93
71	FUNCTIONAL INTERFACE	94	FUNCTIONAL INTERFACE
72	The following convinience methods are provided by this module. They are	95	The following convenience methods are provided by this module. They are
73	exported by default:	96	exported by default:
74		97
75	$json_text = to_json $perl_scalar	98	$json_text = encode_json $perl_scalar
76	Converts the given Perl data structure (a simple scalar or a	99	Converts the given Perl data structure to a UTF-8 encoded, binary
77	reference to a hash or array) to a UTF-8 encoded, binary string
78	(that is, the string contains octets only). Croaks on error.	100	string (that is, the string contains octets only). Croaks on error.
79		101
80	This function call is functionally identical to:	102	This function call is functionally identical to:
81		103
82	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	104	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
83		105
84	except being faster.	106	Except being faster.
85		107
86	$perl_scalar = from_json $json_text	108	$perl_scalar = decode_json $json_text
87	The opposite of "to_json": expects an UTF-8 (binary) string and	109	The opposite of "encode_json": expects an UTF-8 (binary) string and
88	tries to parse that as an UTF-8 encoded JSON text, returning the	110	tries to parse that as an UTF-8 encoded JSON text, returning the
89	resulting simple scalar or reference. Croaks on error.	111	resulting reference. Croaks on error.
90		112
91	This function call is functionally identical to:	113	This function call is functionally identical to:
92		114
93	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	115	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
94		116
95	except being faster.	117	Except being faster.
		118
		119	$is_boolean = JSON::XS::is_bool $scalar
		120	Returns true if the passed scalar represents either JSON::XS::true
		121	or JSON::XS::false, two constants that act like 1 and 0,
		122	respectively and are used to represent JSON "true" and "false"
		123	values in Perl.
		124
		125	See MAPPING, below, for more information on how JSON values are
		126	mapped to Perl.
		127
		128	A FEW NOTES ON UNICODE AND PERL
		129	Since this often leads to confusion, here are a few very clear words on
		130	how Unicode works in Perl, modulo bugs.
		131
		132	1. Perl strings can store characters with ordinal values > 255.
		133	This enables you to store Unicode characters as single characters in
		134	a Perl string - very natural.
		135
		136	2. Perl does not associate an encoding with your strings.
		137	... until you force it to, e.g. when matching it against a regex, or
		138	printing the scalar to a file, in which case Perl either interprets
		139	your string as locale-encoded text, octets/binary, or as Unicode,
		140	depending on various settings. In no case is an encoding stored
		141	together with your data, it is use that decides encoding, not any
		142	magical meta data.
		143
		144	3. The internal utf-8 flag has no meaning with regards to the encoding
		145	of your string.
		146	Just ignore that flag unless you debug a Perl bug, a module written
		147	in XS or want to dive into the internals of perl. Otherwise it will
		148	only confuse you, as, despite the name, it says nothing about how
		149	your string is encoded. You can have Unicode strings with that flag
		150	set, with that flag clear, and you can have binary data with that
		151	flag set and that flag clear. Other possibilities exist, too.
		152
		153	If you didn't know about that flag, just the better, pretend it
		154	doesn't exist.
		155
		156	4. A "Unicode String" is simply a string where each character can be
		157	validly interpreted as a Unicode code point.
		158	If you have UTF-8 encoded data, it is no longer a Unicode string,
		159	but a Unicode string encoded in UTF-8, giving you a binary string.
		160
		161	5. A string containing "high" (> 255) character values is not a UTF-8
		162	string.
		163	It's a fact. Learn to live with it.
		164
		165	I hope this helps :)
96		166
97	OBJECT-ORIENTED INTERFACE	167	OBJECT-ORIENTED INTERFACE
98	The object oriented interface lets you configure your own encoding or	168	The object oriented interface lets you configure your own encoding or
99	decoding style, within the limits of supported formats.	169	decoding style, within the limits of supported formats.
100		170
…		…
108		178
109	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})	179	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
110	=> {"a": [1, 2]}	180	=> {"a": [1, 2]}
111		181
112	$json = $json->ascii ([$enable])	182	$json = $json->ascii ([$enable])
		183	$enabled = $json->get_ascii
113	If $enable is true (or missing), then the "encode" method will not	184	If $enable is true (or missing), then the "encode" method will not
114	generate characters outside the code range 0..127 (which is ASCII).	185	generate characters outside the code range 0..127 (which is ASCII).
115	Any unicode characters outside that range will be escaped using	186	Any Unicode characters outside that range will be escaped using
116	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL	187	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
117	escape sequence, as per RFC4627. The resulting encoded JSON text can	188	escape sequence, as per RFC4627. The resulting encoded JSON text can
118	be treated as a native unicode string, an ascii-encoded,	189	be treated as a native Unicode string, an ascii-encoded,
119	latin1-encoded or UTF-8 encoded string, or any other superset of	190	latin1-encoded or UTF-8 encoded string, or any other superset of
120	ASCII.	191	ASCII.
121		192
122	If $enable is false, then the "encode" method will not escape	193	If $enable is false, then the "encode" method will not escape
123	Unicode characters unless required by the JSON syntax or other	194	Unicode characters unless required by the JSON syntax or other
124	flags. This results in a faster and more compact format.	195	flags. This results in a faster and more compact format.
125		196
		197	See also the section ENCODING/CODESET FLAG NOTES later in this
		198	document.
		199
126	The main use for this flag is to produce JSON texts that can be	200	The main use for this flag is to produce JSON texts that can be
127	transmitted over a 7-bit channel, as the encoded JSON texts will not	201	transmitted over a 7-bit channel, as the encoded JSON texts will not
128	contain any 8 bit characters.	202	contain any 8 bit characters.
129		203
130	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	204	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
131	=> ["\ud801\udc01"]	205	=> ["\ud801\udc01"]
132		206
133	$json = $json->latin1 ([$enable])	207	$json = $json->latin1 ([$enable])
		208	$enabled = $json->get_latin1
134	If $enable is true (or missing), then the "encode" method will	209	If $enable is true (or missing), then the "encode" method will
135	encode the resulting JSON text as latin1 (or iso-8859-1), escaping	210	encode the resulting JSON text as latin1 (or iso-8859-1), escaping
136	any characters outside the code range 0..255. The resulting string	211	any characters outside the code range 0..255. The resulting string
137	can be treated as a latin1-encoded JSON text or a native unicode	212	can be treated as a latin1-encoded JSON text or a native Unicode
138	string. The "decode" method will not be affected in any way by this	213	string. The "decode" method will not be affected in any way by this
139	flag, as "decode" by default expects unicode, which is a strict	214	flag, as "decode" by default expects Unicode, which is a strict
140	superset of latin1.	215	superset of latin1.
141		216
142	If $enable is false, then the "encode" method will not escape	217	If $enable is false, then the "encode" method will not escape
143	Unicode characters unless required by the JSON syntax or other	218	Unicode characters unless required by the JSON syntax or other
144	flags.	219	flags.
		220
		221	See also the section ENCODING/CODESET FLAG NOTES later in this
		222	document.
145		223
146	The main use for this flag is efficiently encoding binary data as	224	The main use for this flag is efficiently encoding binary data as
147	JSON text, as most octets will not be escaped, resulting in a	225	JSON text, as most octets will not be escaped, resulting in a
148	smaller encoded size. The disadvantage is that the resulting JSON	226	smaller encoded size. The disadvantage is that the resulting JSON
149	text is encoded in latin1 (and must correctly be treated as such	227	text is encoded in latin1 (and must correctly be treated as such
150	when storing and transfering), a rare encoding for JSON. It is	228	when storing and transferring), a rare encoding for JSON. It is
151	therefore most useful when you want to store data structures known	229	therefore most useful when you want to store data structures known
152	to contain binary data efficiently in files or databases, not when	230	to contain binary data efficiently in files or databases, not when
153	talking to other JSON encoders/decoders.	231	talking to other JSON encoders/decoders.
154		232
155	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]	233	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
156	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)	234	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
157		235
158	$json = $json->utf8 ([$enable])	236	$json = $json->utf8 ([$enable])
		237	$enabled = $json->get_utf8
159	If $enable is true (or missing), then the "encode" method will	238	If $enable is true (or missing), then the "encode" method will
160	encode the JSON result into UTF-8, as required by many protocols,	239	encode the JSON result into UTF-8, as required by many protocols,
161	while the "decode" method expects to be handled an UTF-8-encoded	240	while the "decode" method expects to be handled an UTF-8-encoded
162	string. Please note that UTF-8-encoded strings do not contain any	241	string. Please note that UTF-8-encoded strings do not contain any
163	characters outside the range 0..255, they are thus useful for	242	characters outside the range 0..255, they are thus useful for
164	bytewise/binary I/O. In future versions, enabling this option might	243	bytewise/binary I/O. In future versions, enabling this option might
165	enable autodetection of the UTF-16 and UTF-32 encoding families, as	244	enable autodetection of the UTF-16 and UTF-32 encoding families, as
166	described in RFC4627.	245	described in RFC4627.
167		246
168	If $enable is false, then the "encode" method will return the JSON	247	If $enable is false, then the "encode" method will return the JSON
169	string as a (non-encoded) unicode string, while "decode" expects	248	string as a (non-encoded) Unicode string, while "decode" expects
170	thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or	249	thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or
171	UTF-16) needs to be done yourself, e.g. using the Encode module.	250	UTF-16) needs to be done yourself, e.g. using the Encode module.
		251
		252	See also the section ENCODING/CODESET FLAG NOTES later in this
		253	document.
172		254
173	Example, output UTF-16BE-encoded JSON:	255	Example, output UTF-16BE-encoded JSON:
174		256
175	use Encode;	257	use Encode;
176	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	258	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
195	2	277	2
196	]	278	]
197	}	279	}
198		280
199	$json = $json->indent ([$enable])	281	$json = $json->indent ([$enable])
		282	$enabled = $json->get_indent
200	If $enable is true (or missing), then the "encode" method will use a	283	If $enable is true (or missing), then the "encode" method will use a
201	multiline format as output, putting every array member or	284	multiline format as output, putting every array member or
202	object/hash key-value pair into its own line, identing them	285	object/hash key-value pair into its own line, indenting them
203	properly.	286	properly.
204		287
205	If $enable is false, no newlines or indenting will be produced, and	288	If $enable is false, no newlines or indenting will be produced, and
206	the resulting JSON text is guarenteed not to contain any "newlines".	289	the resulting JSON text is guaranteed not to contain any "newlines".
207		290
208	This setting has no effect when decoding JSON texts.	291	This setting has no effect when decoding JSON texts.
209		292
210	$json = $json->space_before ([$enable])	293	$json = $json->space_before ([$enable])
		294	$enabled = $json->get_space_before
211	If $enable is true (or missing), then the "encode" method will add	295	If $enable is true (or missing), then the "encode" method will add
212	an extra optional space before the ":" separating keys from values	296	an extra optional space before the ":" separating keys from values
213	in JSON objects.	297	in JSON objects.
214		298
215	If $enable is false, then the "encode" method will not add any extra	299	If $enable is false, then the "encode" method will not add any extra
…		…
221	Example, space_before enabled, space_after and indent disabled:	305	Example, space_before enabled, space_after and indent disabled:
222		306
223	{"key" :"value"}	307	{"key" :"value"}
224		308
225	$json = $json->space_after ([$enable])	309	$json = $json->space_after ([$enable])
		310	$enabled = $json->get_space_after
226	If $enable is true (or missing), then the "encode" method will add	311	If $enable is true (or missing), then the "encode" method will add
227	an extra optional space after the ":" separating keys from values in	312	an extra optional space after the ":" separating keys from values in
228	JSON objects and extra whitespace after the "," separating key-value	313	JSON objects and extra whitespace after the "," separating key-value
229	pairs and array members.	314	pairs and array members.
230		315
…		…
235		320
236	Example, space_before and indent disabled, space_after enabled:	321	Example, space_before and indent disabled, space_after enabled:
237		322
238	{"key": "value"}	323	{"key": "value"}
239		324
		325	$json = $json->relaxed ([$enable])
		326	$enabled = $json->get_relaxed
		327	If $enable is true (or missing), then "decode" will accept some
		328	extensions to normal JSON syntax (see below). "encode" will not be
		329	affected in anyway. *Be aware that this option makes you accept
		330	invalid JSON texts as if they were valid!*. I suggest only to use
		331	this option to parse application-specific files written by humans
		332	(configuration files, resource files etc.)
		333
		334	If $enable is false (the default), then "decode" will only accept
		335	valid JSON texts.
		336
		337	Currently accepted extensions are:
		338
		339	* list items can have an end-comma
		340
		341	JSON separates array elements and key-value pairs with commas.
		342	This can be annoying if you write JSON texts manually and want
		343	to be able to quickly append elements, so this extension accepts
		344	comma at the end of such items not just between them:
		345
		346	[
		347	1,
		348	2, <- this comma not normally allowed
		349	]
		350	{
		351	"k1": "v1",
		352	"k2": "v2", <- this comma not normally allowed
		353	}
		354
		355	* shell-style '#'-comments
		356
		357	Whenever JSON allows whitespace, shell-style comments are
		358	additionally allowed. They are terminated by the first
		359	carriage-return or line-feed character, after which more
		360	white-space and comments are allowed.
		361
		362	[
		363	1, # this comment not allowed in JSON
		364	# neither this one...
		365	]
		366
240	$json = $json->canonical ([$enable])	367	$json = $json->canonical ([$enable])
		368	$enabled = $json->get_canonical
241	If $enable is true (or missing), then the "encode" method will	369	If $enable is true (or missing), then the "encode" method will
242	output JSON objects by sorting their keys. This is adding a	370	output JSON objects by sorting their keys. This is adding a
243	comparatively high overhead.	371	comparatively high overhead.
244		372
245	If $enable is false, then the "encode" method will output key-value	373	If $enable is false, then the "encode" method will output key-value
246	pairs in the order Perl stores them (which will likely change	374	pairs in the order Perl stores them (which will likely change
247	between runs of the same script).	375	between runs of the same script).
248		376
249	This option is useful if you want the same data structure to be	377	This option is useful if you want the same data structure to be
250	encoded as the same JSON text (given the same overall settings). If	378	encoded as the same JSON text (given the same overall settings). If
251	it is disabled, the same hash migh be encoded differently even if	379	it is disabled, the same hash might be encoded differently even if
252	contains the same data, as key-value pairs have no inherent ordering	380	contains the same data, as key-value pairs have no inherent ordering
253	in Perl.	381	in Perl.
254		382
255	This setting has no effect when decoding JSON texts.	383	This setting has no effect when decoding JSON texts.
256		384
257	$json = $json->allow_nonref ([$enable])	385	$json = $json->allow_nonref ([$enable])
		386	$enabled = $json->get_allow_nonref
258	If $enable is true (or missing), then the "encode" method can	387	If $enable is true (or missing), then the "encode" method can
259	convert a non-reference into its corresponding string, number or	388	convert a non-reference into its corresponding string, number or
260	null JSON value, which is an extension to RFC4627. Likewise,	389	null JSON value, which is an extension to RFC4627. Likewise,
261	"decode" will accept those JSON values instead of croaking.	390	"decode" will accept those JSON values instead of croaking.
262		391
…		…
269	"allow_nonref", resulting in an invalid JSON text:	398	"allow_nonref", resulting in an invalid JSON text:
270		399
271	JSON::XS->new->allow_nonref->encode ("Hello, World!")	400	JSON::XS->new->allow_nonref->encode ("Hello, World!")
272	=> "Hello, World!"	401	=> "Hello, World!"
273		402
		403	$json = $json->allow_unknown ([$enable])
		404	$enabled = $json->get_allow_unknown
		405	If $enable is true (or missing), then "encode" will not throw an
		406	exception when it encounters values it cannot represent in JSON (for
		407	example, filehandles) but instead will encode a JSON "null" value.
		408	Note that blessed objects are not included here and are handled
		409	separately by c<allow_nonref>.
		410
		411	If $enable is false (the default), then "encode" will throw an
		412	exception when it encounters anything it cannot encode as JSON.
		413
		414	This option does not affect "decode" in any way, and it is
		415	recommended to leave it off unless you know your communications
		416	partner.
		417
		418	$json = $json->allow_blessed ([$enable])
		419	$enabled = $json->get_allow_blessed
		420	If $enable is true (or missing), then the "encode" method will not
		421	barf when it encounters a blessed reference. Instead, the value of
		422	the convert_blessed option will decide whether "null"
		423	("convert_blessed" disabled or no "TO_JSON" method found) or a
		424	representation of the object ("convert_blessed" enabled and
		425	"TO_JSON" method found) is being encoded. Has no effect on "decode".
		426
		427	If $enable is false (the default), then "encode" will throw an
		428	exception when it encounters a blessed object.
		429
		430	$json = $json->convert_blessed ([$enable])
		431	$enabled = $json->get_convert_blessed
		432	If $enable is true (or missing), then "encode", upon encountering a
		433	blessed object, will check for the availability of the "TO_JSON"
		434	method on the object's class. If found, it will be called in scalar
		435	context and the resulting scalar will be encoded instead of the
		436	object. If no "TO_JSON" method is found, the value of
		437	"allow_blessed" will decide what to do.
		438
		439	The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
		440	returns other blessed objects, those will be handled in the same
		441	way. "TO_JSON" must take care of not causing an endless recursion
		442	cycle (== crash) in this case. The name of "TO_JSON" was chosen
		443	because other methods called by the Perl core (== not by the user of
		444	the object) are usually in upper case letters and to avoid
		445	collisions with any "to_json" function or method.
		446
		447	This setting does not yet influence "decode" in any way, but in the
		448	future, global hooks might get installed that influence "decode" and
		449	are enabled by this setting.
		450
		451	If $enable is false, then the "allow_blessed" setting will decide
		452	what to do when a blessed object is found.
		453
		454	$json = $json->filter_json_object ([$coderef->($hashref)])
		455	When $coderef is specified, it will be called from "decode" each
		456	time it decodes a JSON object. The only argument is a reference to
		457	the newly-created hash. If the code references returns a single
		458	scalar (which need not be a reference), this value (i.e. a copy of
		459	that scalar to avoid aliasing) is inserted into the deserialised
		460	data structure. If it returns an empty list (NOTE: not "undef",
		461	which is a valid scalar), the original deserialised hash will be
		462	inserted. This setting can slow down decoding considerably.
		463
		464	When $coderef is omitted or undefined, any existing callback will be
		465	removed and "decode" will not change the deserialised hash in any
		466	way.
		467
		468	Example, convert all JSON objects into the integer 5:
		469
		470	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		471	# returns [5]
		472	$js->decode ('[{}]')
		473	# throw an exception because allow_nonref is not enabled
		474	# so a lone 5 is not allowed.
		475	$js->decode ('{"a":1, "b":2}');
		476
		477	$json = $json->filter_json_single_key_object ($key [=>
		478	$coderef->($value)])
		479	Works remotely similar to "filter_json_object", but is only called
		480	for JSON objects having a single key named $key.
		481
		482	This $coderef is called before the one specified via
		483	"filter_json_object", if any. It gets passed the single value in the
		484	JSON object. If it returns a single value, it will be inserted into
		485	the data structure. If it returns nothing (not even "undef" but the
		486	empty list), the callback from "filter_json_object" will be called
		487	next, as if no single-key callback were specified.
		488
		489	If $coderef is omitted or undefined, the corresponding callback will
		490	be disabled. There can only ever be one callback for a given key.
		491
		492	As this callback gets called less often then the
		493	"filter_json_object" one, decoding speed will not usually suffer as
		494	much. Therefore, single-key objects make excellent targets to
		495	serialise Perl objects into, especially as single-key JSON objects
		496	are as close to the type-tagged value concept as JSON gets (it's
		497	basically an ID/VALUE tuple). Of course, JSON does not support this
		498	in any way, so you need to make sure your data never looks like a
		499	serialised Perl hash.
		500
		501	Typical names for the single object key are "__class_whatever__", or
		502	"$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
		503	things like "__class_md5sum(classname)__", to reduce the risk of
		504	clashing with real hashes.
		505
		506	Example, decode JSON objects of the form "{ "__widget__" => <id> }"
		507	into the corresponding $WIDGET{<id>} object:
		508
		509	# return whatever is in $WIDGET{5}:
		510	JSON::XS
		511	->new
		512	->filter_json_single_key_object (__widget__ => sub {
		513	$WIDGET{ $_[0] }
		514	})
		515	->decode ('{"__widget__": 5')
		516
		517	# this can be used with a TO_JSON method in some "widget" class
		518	# for serialisation to json:
		519	sub WidgetBase::TO_JSON {
		520	my ($self) = @_;
		521
		522	unless ($self->{id}) {
		523	$self->{id} = ..get..some..id..;
		524	$WIDGET{$self->{id}} = $self;
		525	}
		526
		527	{ __widget__ => $self->{id} }
		528	}
		529
274	$json = $json->shrink ([$enable])	530	$json = $json->shrink ([$enable])
		531	$enabled = $json->get_shrink
275	Perl usually over-allocates memory a bit when allocating space for	532	Perl usually over-allocates memory a bit when allocating space for
276	strings. This flag optionally resizes strings generated by either	533	strings. This flag optionally resizes strings generated by either
277	"encode" or "decode" to their minimum size possible. This can save	534	"encode" or "decode" to their minimum size possible. This can save
278	memory when your JSON texts are either very very long or you have	535	memory when your JSON texts are either very very long or you have
279	many short strings. It will also try to downgrade any strings to	536	many short strings. It will also try to downgrade any strings to
…		…
297	converting strings that look like integers or floats into integers	554	converting strings that look like integers or floats into integers
298	or floats internally (there is no difference on the Perl level),	555	or floats internally (there is no difference on the Perl level),
299	saving space.	556	saving space.
300		557
301	$json = $json->max_depth ([$maximum_nesting_depth])	558	$json = $json->max_depth ([$maximum_nesting_depth])
		559	$max_depth = $json->get_max_depth
302	Sets the maximum nesting level (default 512) accepted while encoding	560	Sets the maximum nesting level (default 512) accepted while encoding
303	or decoding. If the JSON text or Perl data structure has an equal or	561	or decoding. If a higher nesting level is detected in JSON text or a
304	higher nesting level then this limit, then the encoder and decoder	562	Perl data structure, then the encoder and decoder will stop and
305	will stop and croak at that point.	563	croak at that point.
306		564
307	Nesting level is defined by number of hash- or arrayrefs that the	565	Nesting level is defined by number of hash- or arrayrefs that the
308	encoder needs to traverse to reach a given point or the number of	566	encoder needs to traverse to reach a given point or the number of
309	"{" or "[" characters without their matching closing parenthesis	567	"{" or "[" characters without their matching closing parenthesis
310	crossed to reach a given character in a string.	568	crossed to reach a given character in a string.
311		569
312	Setting the maximum depth to one disallows any nesting, so that	570	Setting the maximum depth to one disallows any nesting, so that
313	ensures that the object is only a single hash/object or array.	571	ensures that the object is only a single hash/object or array.
314		572
315	The argument to "max_depth" will be rounded up to the next nearest	573	If no argument is given, the highest possible setting will be used,
316	power of two.	574	which is rarely useful.
		575
		576	Note that nesting is implemented by recursion in C. The default
		577	value has been chosen to be as large as typical operating systems
		578	allow without crashing.
		579
		580	See SECURITY CONSIDERATIONS, below, for more info on why this is
		581	useful.
		582
		583	$json = $json->max_size ([$maximum_string_size])
		584	$max_size = $json->get_max_size
		585	Set the maximum length a JSON text may have (in bytes) where
		586	decoding is being attempted. The default is 0, meaning no limit.
		587	When "decode" is called on a string that is longer then this many
		588	bytes, it will not attempt to decode the string but throw an
		589	exception. This setting has no effect on "encode" (yet).
		590
		591	If no argument is given, the limit check will be deactivated (same
		592	as when 0 is specified).
317		593
318	See SECURITY CONSIDERATIONS, below, for more info on why this is	594	See SECURITY CONSIDERATIONS, below, for more info on why this is
319	useful.	595	useful.
320		596
321	$json_text = $json->encode ($perl_scalar)	597	$json_text = $json->encode ($perl_scalar)
…		…
346	and you need to know where the JSON text ends.	622	and you need to know where the JSON text ends.
347		623
348	JSON::XS->new->decode_prefix ("[1] the tail")	624	JSON::XS->new->decode_prefix ("[1] the tail")
349	=> ([], 3)	625	=> ([], 3)
350		626
		627	INCREMENTAL PARSING
		628	In some cases, there is the need for incremental parsing of JSON texts.
		629	While this module always has to keep both JSON text and resulting Perl
		630	data structure in memory at one time, it does allow you to parse a JSON
		631	stream incrementally. It does so by accumulating text until it has a
		632	full JSON object, which it then can decode. This process is similar to
		633	using "decode_prefix" to see if a full JSON object is available, but is
		634	much more efficient (JSON::XS will only attempt to parse the JSON text
		635	once it is sure it has enough text to get a decisive result, using a
		636	very simple but truly incremental parser).
		637
		638	The following two methods deal with this.
		639
		640	[void, scalar or list context] = $json->incr_parse ([$string])
		641	This is the central parsing function. It can both append new text
		642	and extract objects from the stream accumulated so far (both of
		643	these functions are optional).
		644
		645	If $string is given, then this string is appended to the already
		646	existing JSON fragment stored in the $json object.
		647
		648	After that, if the function is called in void context, it will
		649	simply return without doing anything further. This can be used to
		650	add more text in as many chunks as you want.
		651
		652	If the method is called in scalar context, then it will try to
		653	extract exactly one JSON object. If that is successful, it will
		654	return this object, otherwise it will return "undef". If there is a
		655	parse error, this method will croak just as "decode" would do (one
		656	can then use "incr_skip" to skip the errornous part). This is the
		657	most common way of using the method.
		658
		659	And finally, in list context, it will try to extract as many objects
		660	from the stream as it can find and return them, or the empty list
		661	otherwise. For this to work, there must be no separators between the
		662	JSON objects or arrays, instead they must be concatenated
		663	back-to-back. If an error occurs, an exception will be raised as in
		664	the scalar context case. Note that in this case, any
		665	previously-parsed JSON texts will be lost.
		666
		667	$lvalue_string = $json->incr_text
		668	This method returns the currently stored JSON fragment as an lvalue,
		669	that is, you can manipulate it. This only works when a preceding
		670	call to "incr_parse" in scalar context successfully returned an
		671	object. Under all other circumstances you must not call this
		672	function (I mean it. although in simple tests it might actually
		673	work, it will fail under real world conditions). As a special
		674	exception, you can also call this method before having parsed
		675	anything.
		676
		677	This function is useful in two cases: a) finding the trailing text
		678	after a JSON object or b) parsing multiple JSON objects separated by
		679	non-JSON text (such as commas).
		680
		681	$json->incr_skip
		682	This will reset the state of the incremental parser and will remove
		683	the parsed text from the input buffer. This is useful after
		684	"incr_parse" died, in which case the input buffer and incremental
		685	parser state is left unchanged, to skip the text parsed so far and
		686	to reset the parse state.
		687
		688	$json->incr_reset
		689	This completely resets the incremental parser, that is, after this
		690	call, it will be as if the parser had never parsed anything.
		691
		692	This is useful if you want ot repeatedly parse JSON objects and want
		693	to ignore any trailing data, which means you have to reset the
		694	parser after each successful decode.
		695
		696	LIMITATIONS
		697	All options that affect decoding are supported, except "allow_nonref".
		698	The reason for this is that it cannot be made to work sensibly: JSON
		699	objects and arrays are self-delimited, i.e. you can concatenate them
		700	back to back and still decode them perfectly. This does not hold true
		701	for JSON numbers, however.
		702
		703	For example, is the string 1 a single JSON number, or is it simply the
		704	start of 12? Or is 12 a single JSON number, or the concatenation of 1
		705	and 2? In neither case you can tell, and this is why JSON::XS takes the
		706	conservative route and disallows this case.
		707
		708	EXAMPLES
		709	Some examples will make all this clearer. First, a simple example that
		710	works similarly to "decode_prefix": We want to decode the JSON object at
		711	the start of a string and identify the portion after the JSON object:
		712
		713	my $text = "[1,2,3] hello";
		714
		715	my $json = new JSON::XS;
		716
		717	my $obj = $json->incr_parse ($text)
		718	or die "expected JSON object or array at beginning of string";
		719
		720	my $tail = $json->incr_text;
		721	# $tail now contains " hello"
		722
		723	Easy, isn't it?
		724
		725	Now for a more complicated example: Imagine a hypothetical protocol
		726	where you read some requests from a TCP stream, and each request is a
		727	JSON array, without any separation between them (in fact, it is often
		728	useful to use newlines as "separators", as these get interpreted as
		729	whitespace at the start of the JSON text, which makes it possible to
		730	test said protocol with "telnet"...).
		731
		732	Here is how you'd do it (it is trivial to write this in an event-based
		733	manner):
		734
		735	my $json = new JSON::XS;
		736
		737	# read some data from the socket
		738	while (sysread $socket, my $buf, 4096) {
		739
		740	# split and decode as many requests as possible
		741	for my $request ($json->incr_parse ($buf)) {
		742	# act on the $request
		743	}
		744	}
		745
		746	Another complicated example: Assume you have a string with JSON objects
		747	or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
		748	[3]"). To parse them, we have to skip the commas between the JSON texts,
		749	and here is where the lvalue-ness of "incr_text" comes in useful:
		750
		751	my $text = "[1],[2], [3]";
		752	my $json = new JSON::XS;
		753
		754	# void context, so no parsing done
		755	$json->incr_parse ($text);
		756
		757	# now extract as many objects as possible. note the
		758	# use of scalar context so incr_text can be called.
		759	while (my $obj = $json->incr_parse) {
		760	# do something with $obj
		761
		762	# now skip the optional comma
		763	$json->incr_text =~ s/^ \s* , //x;
		764	}
		765
		766	Now lets go for a very complex example: Assume that you have a gigantic
		767	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		768	but you cannot load it into memory fully (this has actually happened in
		769	the real world :).
		770
		771	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		772	can still help you: You implement a (very simple) array parser and let
		773	JSON decode the array elements, which are all full JSON objects on their
		774	own (this wouldn't work if the array elements could be JSON numbers, for
		775	example):
		776
		777	my $json = new JSON::XS;
		778
		779	# open the monster
		780	open my $fh, "<bigfile.json"
		781	or die "bigfile: $!";
		782
		783	# first parse the initial "["
		784	for (;;) {
		785	sysread $fh, my $buf, 65536
		786	or die "read error: $!";
		787	$json->incr_parse ($buf); # void context, so no parsing
		788
		789	# Exit the loop once we found and removed(!) the initial "[".
		790	# In essence, we are (ab-)using the $json object as a simple scalar
		791	# we append data to.
		792	last if $json->incr_text =~ s/^ \s* \[ //x;
		793	}
		794
		795	# now we have the skipped the initial "[", so continue
		796	# parsing all the elements.
		797	for (;;) {
		798	# in this loop we read data until we got a single JSON object
		799	for (;;) {
		800	if (my $obj = $json->incr_parse) {
		801	# do something with $obj
		802	last;
		803	}
		804
		805	# add more data
		806	sysread $fh, my $buf, 65536
		807	or die "read error: $!";
		808	$json->incr_parse ($buf); # void context, so no parsing
		809	}
		810
		811	# in this loop we read data until we either found and parsed the
		812	# separating "," between elements, or the final "]"
		813	for (;;) {
		814	# first skip whitespace
		815	$json->incr_text =~ s/^\s*//;
		816
		817	# if we find "]", we are done
		818	if ($json->incr_text =~ s/^\]//) {
		819	print "finished.\n";
		820	exit;
		821	}
		822
		823	# if we find ",", we can continue with the next element
		824	if ($json->incr_text =~ s/^,//) {
		825	last;
		826	}
		827
		828	# if we find anything else, we have a parse error!
		829	if (length $json->incr_text) {
		830	die "parse error near ", $json->incr_text;
		831	}
		832
		833	# else add more data
		834	sysread $fh, my $buf, 65536
		835	or die "read error: $!";
		836	$json->incr_parse ($buf); # void context, so no parsing
		837	}
		838
		839	This is a complex example, but most of the complexity comes from the
		840	fact that we are trying to be correct (bear with me if I am wrong, I
		841	never ran the above example :).
		842
351	MAPPING	843	MAPPING
352	This section describes how JSON::XS maps Perl values to JSON values and	844	This section describes how JSON::XS maps Perl values to JSON values and
353	vice versa. These mappings are designed to "do the right thing" in most	845	vice versa. These mappings are designed to "do the right thing" in most
354	circumstances automatically, preserving round-tripping characteristics	846	circumstances automatically, preserving round-tripping characteristics
355	(what you put in comes out as something equivalent).	847	(what you put in comes out as something equivalent).
356		848
357	For the more enlightened: note that in the following descriptions,	849	For the more enlightened: note that in the following descriptions,
358	lowercase perl refers to the Perl interpreter, while uppcercase Perl	850	lowercase perl refers to the Perl interpreter, while uppercase Perl
359	refers to the abstract Perl language itself.	851	refers to the abstract Perl language itself.
360		852
361	JSON -> PERL	853	JSON -> PERL
362	object	854	object
363	A JSON object becomes a reference to a hash in Perl. No ordering of	855	A JSON object becomes a reference to a hash in Perl. No ordering of
364	object keys is preserved (JSON does not preserver object key	856	object keys is preserved (JSON does not preserve object key ordering
365	ordering itself).	857	itself).
366		858
367	array	859	array
368	A JSON array becomes a reference to an array in Perl.	860	A JSON array becomes a reference to an array in Perl.
369		861
370	string	862	string
371	A JSON string becomes a string scalar in Perl - Unicode codepoints	863	A JSON string becomes a string scalar in Perl - Unicode codepoints
372	in JSON are represented by the same codepoints in the Perl string,	864	in JSON are represented by the same codepoints in the Perl string,
373	so no manual decoding is necessary.	865	so no manual decoding is necessary.
374		866
375	number	867	number
376	A JSON number becomes either an integer or numeric (floating point)	868	A JSON number becomes either an integer, numeric (floating point) or
377	scalar in perl, depending on its range and any fractional parts. On	869	string scalar in perl, depending on its range and any fractional
378	the Perl level, there is no difference between those as Perl handles	870	parts. On the Perl level, there is no difference between those as
379	all the conversion details, but an integer may take slightly less	871	Perl handles all the conversion details, but an integer may take
380	memory and might represent more values exactly than (floating point)	872	slightly less memory and might represent more values exactly than
		873	floating point numbers.
		874
		875	If the number consists of digits only, JSON::XS will try to
		876	represent it as an integer value. If that fails, it will try to
		877	represent it as a numeric (floating point) value if that is possible
		878	without loss of precision. Otherwise it will preserve the number as
		879	a string value (in which case you lose roundtripping ability, as the
		880	JSON number will be re-encoded toa JSON string).
		881
		882	Numbers containing a fractional or exponential part will always be
		883	represented as numeric (floating point) values, possibly at a loss
		884	of precision (in which case you might lose perfect roundtripping
		885	ability, but the JSON number will still be re-encoded as a JSON
381	numbers.	886	number).
382		887
383	true, false	888	true, false
384	These JSON atoms become 0, 1, respectively. Information is lost in	889	These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
385	this process. Future versions might represent those values	890	respectively. They are overloaded to act almost exactly like the
386	differently, but they will be guarenteed to act like these integers	891	numbers 1 and 0. You can check whether a scalar is a JSON boolean by
387	would normally in Perl.	892	using the "JSON::XS::is_bool" function.
388		893
389	null	894	null
390	A JSON null atom becomes "undef" in Perl.	895	A JSON null atom becomes "undef" in Perl.
391		896
392	PERL -> JSON	897	PERL -> JSON
…		…
414	an exception to be thrown, except for references to the integers 0	919	an exception to be thrown, except for references to the integers 0
415	and 1, which get turned into "false" and "true" atoms in JSON. You	920	and 1, which get turned into "false" and "true" atoms in JSON. You
416	can also use "JSON::XS::false" and "JSON::XS::true" to improve	921	can also use "JSON::XS::false" and "JSON::XS::true" to improve
417	readability.	922	readability.
418		923
419	to_json [\0,JSON::XS::true] # yields [false,true]	924	encode_json [\0, JSON::XS::true] # yields [false,true]
		925
		926	JSON::XS::true, JSON::XS::false
		927	These special values become JSON true and JSON false values,
		928	respectively. You can also use "\1" and "\0" directly if you want.
420		929
421	blessed objects	930	blessed objects
422	Blessed objects are not allowed. JSON::XS currently tries to encode	931	Blessed objects are not directly representable in JSON. See the
423	their underlying representation (hash- or arrayref), but this	932	"allow_blessed" and "convert_blessed" methods on various options on
424	behaviour might change in future versions.	933	how to deal with this: basically, you can choose between throwing an
		934	exception, encoding the reference as if it weren't blessed, or
		935	provide your own serialiser method.
425		936
426	simple scalars	937	simple scalars
427	Simple Perl scalars (any scalar that is not a reference) are the	938	Simple Perl scalars (any scalar that is not a reference) are the
428	most difficult objects to encode: JSON::XS will encode undefined	939	most difficult objects to encode: JSON::XS will encode undefined
429	scalars as JSON null value, scalars that have last been used in a	940	scalars as JSON "null" values, scalars that have last been used in a
430	string context before encoding as JSON strings and anything else as	941	string context before encoding as JSON strings, and anything else as
431	number value:	942	number value:
432		943
433	# dump as number	944	# dump as number
434	to_json [2] # yields [2]	945	encode_json [2] # yields [2]
435	to_json [-3.0e17] # yields [-3e+17]	946	encode_json [-3.0e17] # yields [-3e+17]
436	my $value = 5; to_json [$value] # yields [5]	947	my $value = 5; encode_json [$value] # yields [5]
437		948
438	# used as string, so dump as string	949	# used as string, so dump as string
439	print $value;	950	print $value;
440	to_json [$value] # yields ["5"]	951	encode_json [$value] # yields ["5"]
441		952
442	# undef becomes null	953	# undef becomes null
443	to_json [undef] # yields [null]	954	encode_json [undef] # yields [null]
444		955
445	You can force the type to be a string by stringifying it:	956	You can force the type to be a JSON string by stringifying it:
446		957
447	my $x = 3.1; # some variable containing a number	958	my $x = 3.1; # some variable containing a number
448	"$x"; # stringified	959	"$x"; # stringified
449	$x .= ""; # another, more awkward way to stringify	960	$x .= ""; # another, more awkward way to stringify
450	print $x; # perl does it for you, too, quite often	961	print $x; # perl does it for you, too, quite often
451		962
452	You can force the type to be a number by numifying it:	963	You can force the type to be a JSON number by numifying it:
453		964
454	my $x = "3"; # some variable containing a string	965	my $x = "3"; # some variable containing a string
455	$x += 0; # numify it, ensuring it will be dumped as a number	966	$x += 0; # numify it, ensuring it will be dumped as a number
456	$x *= 1; # same thing, the choise is yours.	967	$x *= 1; # same thing, the choice is yours.
457		968
458	You can not currently output JSON booleans or force the type in	969	You can not currently force the type in other, less obscure, ways.
459	other, less obscure, ways. Tell me if you need this capability.	970	Tell me if you need this capability (but don't forget to explain why
		971	it's needed :).
460		972
461	COMPARISON	973	ENCODING/CODESET FLAG NOTES
462	As already mentioned, this module was created because none of the	974	The interested reader might have seen a number of flags that signify
463	existing JSON modules could be made to work correctly. First I will	975	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
464	describe the problems (or pleasures) I encountered with various existing	976	some confusion on what these do, so here is a short comparison:
465	JSON modules, followed by some benchmark values. JSON::XS was designed
466	not to suffer from any of these problems or limitations.
467		977
468	JSON 1.07	978	"utf8" controls whether the JSON text created by "encode" (and expected
469	Slow (but very portable, as it is written in pure Perl).	979	by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
		980	control whether "encode" escapes character values outside their
		981	respective codeset range. Neither of these flags conflict with each
		982	other, although some combinations make less sense than others.
470		983
471	Undocumented/buggy Unicode handling (how JSON handles unicode values	984	Care has been taken to make all flags symmetrical with respect to
472	is undocumented. One can get far by feeding it unicode strings and	985	"encode" and "decode", that is, texts encoded with any combination of
473	doing en-/decoding oneself, but unicode escapes are not working	986	these flag values will be correctly decoded when the same flags are used
		987	- in general, if you use different flag settings while encoding vs. when
		988	decoding you likely have a bug somewhere.
		989
		990	Below comes a verbose discussion of these flags. Note that a "codeset"
		991	is simply an abstract set of character-codepoint pairs, while an
		992	encoding takes those codepoint numbers and encodes them, in our case
		993	into octets. Unicode is (among other things) a codeset, UTF-8 is an
		994	encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets and
		995	encodings at the same time, which can be confusing.
		996
		997	"utf8" flag disabled
		998	When "utf8" is disabled (the default), then "encode"/"decode"
		999	generate and expect Unicode strings, that is, characters with high
		1000	ordinal Unicode values (> 255) will be encoded as such characters,
		1001	and likewise such characters are decoded as-is, no canges to them
		1002	will be done, except "(re-)interpreting" them as Unicode codepoints
		1003	or Unicode characters, respectively (to Perl, these are the same
		1004	thing in strings unless you do funny/weird/dumb stuff).
		1005
		1006	This is useful when you want to do the encoding yourself (e.g. when
		1007	you want to have UTF-16 encoded JSON texts) or when some other layer
		1008	does the encoding for you (for example, when printing to a terminal
		1009	using a filehandle that transparently encodes to UTF-8 you certainly
		1010	do NOT want to UTF-8 encode your data first and have Perl encode it
		1011	another time).
		1012
		1013	"utf8" flag enabled
		1014	If the "utf8"-flag is enabled, "encode"/"decode" will encode all
		1015	characters using the corresponding UTF-8 multi-byte sequence, and
		1016	will expect your input strings to be encoded as UTF-8, that is, no
		1017	"character" of the input string must have any value > 255, as UTF-8
		1018	does not allow that.
		1019
		1020	The "utf8" flag therefore switches between two modes: disabled means
		1021	you will get a Unicode string in Perl, enabled means you get an
		1022	UTF-8 encoded octet/binary string in Perl.
		1023
		1024	"latin1" or "ascii" flags enabled
		1025	With "latin1" (or "ascii") enabled, "encode" will escape characters
		1026	with ordinal values > 255 (> 127 with "ascii") and encode the
		1027	remaining characters as specified by the "utf8" flag.
		1028
		1029	If "utf8" is disabled, then the result is also correctly encoded in
		1030	those character sets (as both are proper subsets of Unicode, meaning
		1031	that a Unicode string with all character values < 256 is the same
		1032	thing as a ISO-8859-1 string, and a Unicode string with all
		1033	character values < 128 is the same thing as an ASCII string in
474	properly).	1034	Perl).
475		1035
476	No roundtripping (strings get clobbered if they look like numbers,	1036	If "utf8" is enabled, you still get a correct UTF-8-encoded string,
477	e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that	1037	regardless of these flags, just some more characters will be escaped
478	will decode into the number 2.	1038	using "\uXXXX" then before.
479		1039
480	JSON::PC 0.01	1040	Note that ISO-8859-1-encoded strings are not compatible with UTF-8
481	Very fast.	1041	encoding, while ASCII-encoded strings are. That is because the
		1042	ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
		1043	codeset being a subset of Unicode), while ASCII is.
482		1044
483	Undocumented/buggy Unicode handling.	1045	Surprisingly, "decode" will ignore these flags and so treat all
		1046	input values as governed by the "utf8" flag. If it is disabled, this
		1047	allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
		1048	strict subsets of Unicode. If it is enabled, you can correctly
		1049	decode UTF-8 encoded strings.
484		1050
485	No roundtripping.	1051	So neither "latin1" nor "ascii" are incompatible with the "utf8"
		1052	flag - they only govern when the JSON output engine escapes a
		1053	character or not.
486		1054
487	Has problems handling many Perl values (e.g. regex results and other	1055	The main use for "latin1" is to relatively efficiently store binary
488	magic values will make it croak).	1056	data as JSON, at the expense of breaking compatibility with most
		1057	JSON decoders.
489		1058
490	Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"	1059	The main use for "ascii" is to force the output to not contain
491	which is not a valid JSON text.	1060	characters with values > 127, which means you can interpret the
		1061	resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
		1062	any character set and 8-bit-encoding, and still get the same data
		1063	structure back. This is useful when your channel for JSON transfer
		1064	is not 8-bit clean or the encoding might be mangled in between (e.g.
		1065	in mail), and works because ASCII is a proper subset of most 8-bit
		1066	and multibyte encodings in use in the world.
492		1067
493	Unmaintained (maintainer unresponsive for many months, bugs are not	1068	JSON and YAML
494	getting fixed).	1069	You often hear that JSON is a subset of YAML. This is, however, a mass
		1070	hysteria(*) and very far from the truth (as of the time of this
		1071	writing), so let me state it clearly: *in general, there is no way to
		1072	configure JSON::XS to output a data structure as valid YAML* that works
		1073	in all cases.
495		1074
496	JSON::Syck 0.21	1075	If you really must use JSON::XS to generate YAML, you should use this
497	Very buggy (often crashes).	1076	algorithm (subject to change in future versions):
498		1077
499	Very inflexible (no human-readable format supported, format pretty	1078	my $to_yaml = JSON::XS->new->utf8->space_after (1);
500	much undocumented. I need at least a format for easy reading by	1079	my $yaml = $to_yaml->encode ($ref) . "\n";
501	humans and a single-line compact format for use in a protocol, and
502	preferably a way to generate ASCII-only JSON texts).
503		1080
504	Completely broken (and confusingly documented) Unicode handling	1081	This will usually generate JSON texts that also parse as valid YAML.
505	(unicode escapes are not working properly, you need to set	1082	Please note that YAML has hardcoded limits on (simple) object key
506	ImplicitUnicode to different values on en- and decoding to get	1083	lengths that JSON doesn't have and also has different and incompatible
507	symmetric behaviour).	1084	unicode handling, so you should make sure that your hash keys are
		1085	noticeably shorter than the 1024 "stream characters" YAML allows and
		1086	that you do not have characters with codepoint values outside the
		1087	Unicode BMP (basic multilingual page). YAML also does not allow "\/"
		1088	sequences in strings (which JSON::XS does not currently generate, but
		1089	other JSON generators might).
508		1090
509	No roundtripping (simple cases work, but this depends on wether the	1091	There might be other incompatibilities that I am not aware of (or the
510	scalar value was used in a numeric context or not).	1092	YAML specification has been changed yet again - it does so quite often).
		1093	In general you should not try to generate YAML with a JSON generator or
		1094	vice versa, or try to parse JSON with a YAML parser or vice versa:
		1095	chances are high that you will run into severe interoperability problems
		1096	when you least expect it.
511		1097
512	Dumping hashes may skip hash values depending on iterator state.	1098	(*) I have been pressured multiple times by Brian Ingerson (one of the
		1099	authors of the YAML specification) to remove this paragraph, despite
		1100	him acknowledging that the actual incompatibilities exist. As I was
		1101	personally bitten by this "JSON is YAML" lie, I refused and said I
		1102	will continue to educate people about these issues, so others do not
		1103	run into the same problem again and again. After this, Brian called
		1104	me a (quote)complete and worthless idiot(unquote).
513		1105
514	Unmaintained (maintainer unresponsive for many months, bugs are not	1106	In my opinion, instead of pressuring and insulting people who
515	getting fixed).	1107	actually clarify issues with YAML and the wrong statements of some
516		1108	of its proponents, I would kindly suggest reading the JSON spec
517	Does not check input for validity (i.e. will accept non-JSON input	1109	(which is not that difficult or long) and finally make YAML
518	and return "something" instead of raising an exception. This is a	1110	compatible to it, and educating users about the changes, instead of
519	security issue: imagine two banks transfering money between each	1111	spreading lies about the real compatibility for many years and
520	other using JSON. One bank might parse a given non-JSON request and	1112	trying to silence people who point out that it isn't true.
521	deduct money, while the other might reject the transaction with a
522	syntax error. While a good protocol will at least recover, that is
523	extra unnecessary work and the transaction will still not succeed).
524
525	JSON::DWIW 0.04
526	Very fast. Very natural. Very nice.
527
528	Undocumented unicode handling (but the best of the pack. Unicode
529	escapes still don't get parsed properly).
530
531	Very inflexible.
532
533	No roundtripping.
534
535	Does not generate valid JSON texts (key strings are often unquoted,
536	empty keys result in nothing being output)
537
538	Does not check input for validity.
539		1113
540	SPEED	1114	SPEED
541	It seems that JSON::XS is surprisingly fast, as shown in the following	1115	It seems that JSON::XS is surprisingly fast, as shown in the following
542	tables. They have been generated with the help of the "eg/bench" program	1116	tables. They have been generated with the help of the "eg/bench" program
543	in the JSON::XS distribution, to make it easy to compare on your own	1117	in the JSON::XS distribution, to make it easy to compare on your own
544	system.	1118	system.
545		1119
546	First comes a comparison between various modules using a very short	1120	First comes a comparison between various modules using a very short
547	single-line JSON string:	1121	single-line JSON string (also available at
		1122	<http://dist.schmorp.de/misc/json/short.json>).
548		1123
549	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1124	{"method": "handleMessage", "params": ["user1",
550	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1125	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1126	true, false]}
551		1127
552	It shows the number of encodes/decodes per second (JSON::XS uses the	1128	It shows the number of encodes/decodes per second (JSON::XS uses the
553	functional interface, while JSON::XS/2 uses the OO interface with	1129	functional interface, while JSON::XS/2 uses the OO interface with
554	pretty-printing and hashkey sorting enabled). Higher is better:	1130	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
		1131	Higher is better:
555		1132
556	module \| encode \| decode \|	1133	module \| encode \| decode \|
557	-----------\|------------\|------------\|	1134	-----------\|------------\|------------\|
558	JSON \| 7645.468 \| 4208.613 \|	1135	JSON 1.x \| 4990.842 \| 4088.813 \|
559	JSON::DWIW \| 68534.379 \| 79437.576 \|	1136	JSON::DWIW \| 51653.990 \| 71575.154 \|
560	JSON::PC \| 65948.176 \| 78251.940 \|	1137	JSON::PC \| 65948.176 \| 74631.744 \|
561	JSON::Syck \| 23379.621 \| 28416.694 \|	1138	JSON::PP \| 8931.652 \| 3817.168 \|
		1139	JSON::Syck \| 24877.248 \| 27776.848 \|
562	JSON::XS \| 388361.481 \| 199728.762 \|	1140	JSON::XS \| 388361.481 \| 227951.304 \|
563	JSON::XS/2 \| 218453.333 \| 192399.266 \|	1141	JSON::XS/2 \| 227951.304 \| 218453.333 \|
564	JSON::XS/3 \| 338250.323 \| 192399.266 \|	1142	JSON::XS/3 \| 338250.323 \| 218453.333 \|
565	Storable \| 15732.573 \| 28571.553 \|	1143	Storable \| 16500.016 \| 135300.129 \|
566	-----------+------------+------------+	1144	-----------+------------+------------+
567		1145
568	That is, JSON::XS is about five times faster than JSON::DWIW on	1146	That is, JSON::XS is about five times faster than JSON::DWIW on
569	encoding, about three times faster on decoding, and over fourty times	1147	encoding, about three times faster on decoding, and over forty times
570	faster than JSON, even with pretty-printing and key sorting. It also	1148	faster than JSON, even with pretty-printing and key sorting. It also
571	compares favourably to Storable for small amounts of data.	1149	compares favourably to Storable for small amounts of data.
572		1150
573	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1151	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
574	search API (http://nanoref.com/yahooapis/mgPdGg):	1152	search API (<http://dist.schmorp.de/misc/json/long.json>).
575		1153
576	module \| encode \| decode \|	1154	module \| encode \| decode \|
577	-----------\|------------\|------------\|	1155	-----------\|------------\|------------\|
578	JSON \| 254.685 \| 37.665 \|	1156	JSON 1.x \| 55.260 \| 34.971 \|
579	JSON::DWIW \| 1014.244 \| 1087.678 \|	1157	JSON::DWIW \| 825.228 \| 1082.513 \|
580	JSON::PC \| 3602.116 \| 2307.352 \|	1158	JSON::PC \| 3571.444 \| 2394.829 \|
581	JSON::Syck \| 558.035 \| 776.263 \|	1159	JSON::PP \| 210.987 \| 32.574 \|
582	JSON::XS \| 5747.196 \| 3543.684 \|	1160	JSON::Syck \| 552.551 \| 787.544 \|
583	JSON::XS/2 \| 3968.121 \| 3589.170 \|	1161	JSON::XS \| 5780.463 \| 4854.519 \|
584	JSON::XS/3 \| 6105.246 \| 3561.134 \|	1162	JSON::XS/2 \| 3869.998 \| 4798.975 \|
585	Storable \| 4456.337 \| 5320.020 \|	1163	JSON::XS/3 \| 5862.880 \| 4798.975 \|
		1164	Storable \| 4445.002 \| 5235.027 \|
586	-----------+------------+------------+	1165	-----------+------------+------------+
587		1166
588	Again, JSON::XS leads by far.	1167	Again, JSON::XS leads by far (except for Storable which non-surprisingly
		1168	decodes faster).
589		1169
590	On large strings containing lots of high unicode characters, some	1170	On large strings containing lots of high Unicode characters, some
591	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the	1171	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
592	result will be broken due to missing (or wrong) unicode handling. Others	1172	result will be broken due to missing (or wrong) Unicode handling. Others
593	refuse to decode or encode properly, so it was impossible to prepare a	1173	refuse to decode or encode properly, so it was impossible to prepare a
594	fair comparison table for that case.	1174	fair comparison table for that case.
595		1175
596	SECURITY CONSIDERATIONS	1176	SECURITY CONSIDERATIONS
597	When you are using JSON in a protocol, talking to untrusted potentially	1177	When you are using JSON in a protocol, talking to untrusted potentially
…		…
601	have any buffer overflows. Obviously, this module should ensure that and	1181	have any buffer overflows. Obviously, this module should ensure that and
602	I am trying hard on making that true, but you never know.	1182	I am trying hard on making that true, but you never know.
603		1183
604	Second, you need to avoid resource-starving attacks. That means you	1184	Second, you need to avoid resource-starving attacks. That means you
605	should limit the size of JSON texts you accept, or make sure then when	1185	should limit the size of JSON texts you accept, or make sure then when
606	your resources run out, thats just fine (e.g. by using a separate	1186	your resources run out, that's just fine (e.g. by using a separate
607	process that can crash safely). The size of a JSON text in octets or	1187	process that can crash safely). The size of a JSON text in octets or
608	characters is usually a good indication of the size of the resources	1188	characters is usually a good indication of the size of the resources
609	required to decode it into a Perl structure.	1189	required to decode it into a Perl structure. While JSON::XS can check
		1190	the size of the JSON text, it might be too late when you already have it
		1191	in memory, so you might want to check the size before you accept the
		1192	string.
610		1193
611	Third, JSON::XS recurses using the C stack when decoding objects and	1194	Third, JSON::XS recurses using the C stack when decoding objects and
612	arrays. The C stack is a limited resource: for instance, on my amd64	1195	arrays. The C stack is a limited resource: for instance, on my amd64
613	machine with 8MB of stack size I can decode around 180k nested arrays	1196	machine with 8MB of stack size I can decode around 180k nested arrays
614	but only 14k nested JSON objects (due to perl itself recursing deeply on	1197	but only 14k nested JSON objects (due to perl itself recursing deeply on
615	croak to free the temporary). If that is exceeded, the program crashes.	1198	croak to free the temporary). If that is exceeded, the program crashes.
616	to be conservative, the default nesting limit is set to 512. If your	1199	To be conservative, the default nesting limit is set to 512. If your
617	process has a smaller stack, you should adjust this setting accordingly	1200	process has a smaller stack, you should adjust this setting accordingly
618	with the "max_depth" method.	1201	with the "max_depth" method.
619		1202
620	And last but least, something else could bomb you that I forgot to think	1203	Something else could bomb you, too, that I forgot to think of. In that
621	of. In that case, you get to keep the pieces. I am always open for	1204	case, you get to keep the pieces. I am always open for hints, though...
622	hints, though...	1205
		1206	Also keep in mind that JSON::XS might leak contents of your Perl data
		1207	structures in its error messages, so when you serialise sensitive
		1208	information you might want to make sure that exceptions thrown by
		1209	JSON::XS will not end up in front of untrusted eyes.
		1210
		1211	If you are using JSON::XS to return packets to consumption by JavaScript
		1212	scripts in a browser you should have a look at
		1213	<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1214	you are vulnerable to some common attack vectors (which really are
		1215	browser design bugs, but it is still you who will have to deal with it,
		1216	as major browser developers care only for features, not about getting
		1217	security right).
		1218
		1219	THREADS
		1220	This module is not guaranteed to be thread safe and there are no plans
		1221	to change this until Perl gets thread support (as opposed to the
		1222	horribly slow so-called "threads" which are simply slow and bloated
		1223	process simulations - use fork, it's much faster, cheaper, better).
		1224
		1225	(It might actually work, but you have been warned).
623		1226
624	BUGS	1227	BUGS
625	While the goal of this module is to be correct, that unfortunately does	1228	While the goal of this module is to be correct, that unfortunately does
626	not mean its bug-free, only that I think its design is bug-free. It is	1229	not mean it's bug-free, only that I think its design is bug-free. If you
627	still relatively early in its development. If you keep reporting bugs
628	they will be fixed swiftly, though.	1230	keep reporting bugs they will be fixed swiftly, though.
		1231
		1232	Please refrain from using rt.cpan.org or any other bug reporting
		1233	service. I put the contact address into my modules for a reason.
		1234
		1235	SEE ALSO
		1236	The json_xs command line utility for quick experiments.
629		1237
630	AUTHOR	1238	AUTHOR
631	Marc Lehmann <schmorp@schmorp.de>	1239	Marc Lehmann <schmorp@schmorp.de>
632	http://home.schmorp.de/	1240	http://home.schmorp.de/
633		1241

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Comparing JSON-XS/README (file contents): Revision 1.12 by root, Wed Jun 6 18:17:13 2007 UTC vs. Revision 1.26 by root, Tue Jun 3 06:43:45 2008 UTC

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Comparing JSON-XS/README (file contents):
Revision 1.12 by root, Wed Jun 6 18:17:13 2007 UTC vs.
Revision 1.26 by root, Tue Jun 3 06:43:45 2008 UTC