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

Comparing JSON-XS/README (file contents):
Revision 1.14 by root, Sat Jun 23 23:50:03 2007 UTC vs.
Revision 1.34 by root, Thu Mar 11 17:36:09 2010 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.
96		116
97	$is_boolean = JSON::XS::is_bool $scalar	117	$is_boolean = JSON::XS::is_bool $scalar
98	Returns true if the passed scalar represents either JSON::XS::true	118	Returns true if the passed scalar represents either JSON::XS::true
99	or JSON::XS::false, two constants that act like 1 and 0,	119	or JSON::XS::false, two constants that act like 1 and 0,
100	respectively and are used to represent JSON "true" and "false"	120	respectively and are used to represent JSON "true" and "false"
101	values in Perl.	121	values in Perl.
102		122
103	See MAPPING, below, for more information on how JSON values are	123	See MAPPING, below, for more information on how JSON values are
104	mapped to Perl.	124	mapped to Perl.
105		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 :)
		164
106	OBJECT-ORIENTED INTERFACE	165	OBJECT-ORIENTED INTERFACE
107	The object oriented interface lets you configure your own encoding or	166	The object oriented interface lets you configure your own encoding or
108	decoding style, within the limits of supported formats.	167	decoding style, within the limits of supported formats.
109		168
110	$json = new JSON::XS	169	$json = new JSON::XS
117		176
118	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]})
119	=> {"a": [1, 2]}	178	=> {"a": [1, 2]}
120		179
121	$json = $json->ascii ([$enable])	180	$json = $json->ascii ([$enable])
		181	$enabled = $json->get_ascii
122	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
123	generate characters outside the code range 0..127 (which is ASCII).	183	generate characters outside the code range 0..127 (which is ASCII).
124	Any unicode characters outside that range will be escaped using	184	Any Unicode characters outside that range will be escaped using
125	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL	185	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
126	escape sequence, as per RFC4627. The resulting encoded JSON text can	186	escape sequence, as per RFC4627. The resulting encoded JSON text can
127	be treated as a native unicode string, an ascii-encoded,	187	be treated as a native Unicode string, an ascii-encoded,
128	latin1-encoded or UTF-8 encoded string, or any other superset of	188	latin1-encoded or UTF-8 encoded string, or any other superset of
129	ASCII.	189	ASCII.
130		190
131	If $enable is false, then the "encode" method will not escape	191	If $enable is false, then the "encode" method will not escape
132	Unicode characters unless required by the JSON syntax or other	192	Unicode characters unless required by the JSON syntax or other
133	flags. This results in a faster and more compact format.	193	flags. This results in a faster and more compact format.
134		194
		195	See also the section ENCODING/CODESET FLAG NOTES later in this
		196	document.
		197
135	The main use for this flag is to produce JSON texts that can be	198	The main use for this flag is to produce JSON texts that can be
136	transmitted over a 7-bit channel, as the encoded JSON texts will not	199	transmitted over a 7-bit channel, as the encoded JSON texts will not
137	contain any 8 bit characters.	200	contain any 8 bit characters.
138		201
139	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	202	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
140	=> ["\ud801\udc01"]	203	=> ["\ud801\udc01"]
141		204
142	$json = $json->latin1 ([$enable])	205	$json = $json->latin1 ([$enable])
		206	$enabled = $json->get_latin1
143	If $enable is true (or missing), then the "encode" method will	207	If $enable is true (or missing), then the "encode" method will
144	encode the resulting JSON text as latin1 (or iso-8859-1), escaping	208	encode the resulting JSON text as latin1 (or iso-8859-1), escaping
145	any characters outside the code range 0..255. The resulting string	209	any characters outside the code range 0..255. The resulting string
146	can be treated as a latin1-encoded JSON text or a native unicode	210	can be treated as a latin1-encoded JSON text or a native Unicode
147	string. The "decode" method will not be affected in any way by this	211	string. The "decode" method will not be affected in any way by this
148	flag, as "decode" by default expects unicode, which is a strict	212	flag, as "decode" by default expects Unicode, which is a strict
149	superset of latin1.	213	superset of latin1.
150		214
151	If $enable is false, then the "encode" method will not escape	215	If $enable is false, then the "encode" method will not escape
152	Unicode characters unless required by the JSON syntax or other	216	Unicode characters unless required by the JSON syntax or other
153	flags.	217	flags.
		218
		219	See also the section ENCODING/CODESET FLAG NOTES later in this
		220	document.
154		221
155	The main use for this flag is efficiently encoding binary data as	222	The main use for this flag is efficiently encoding binary data as
156	JSON text, as most octets will not be escaped, resulting in a	223	JSON text, as most octets will not be escaped, resulting in a
157	smaller encoded size. The disadvantage is that the resulting JSON	224	smaller encoded size. The disadvantage is that the resulting JSON
158	text is encoded in latin1 (and must correctly be treated as such	225	text is encoded in latin1 (and must correctly be treated as such
159	when storing and transfering), a rare encoding for JSON. It is	226	when storing and transferring), a rare encoding for JSON. It is
160	therefore most useful when you want to store data structures known	227	therefore most useful when you want to store data structures known
161	to contain binary data efficiently in files or databases, not when	228	to contain binary data efficiently in files or databases, not when
162	talking to other JSON encoders/decoders.	229	talking to other JSON encoders/decoders.
163		230
164	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]	231	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
165	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)	232	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
166		233
167	$json = $json->utf8 ([$enable])	234	$json = $json->utf8 ([$enable])
		235	$enabled = $json->get_utf8
168	If $enable is true (or missing), then the "encode" method will	236	If $enable is true (or missing), then the "encode" method will
169	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,
170	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
171	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
172	characters outside the range 0..255, they are thus useful for	240	characters outside the range 0..255, they are thus useful for
173	bytewise/binary I/O. In future versions, enabling this option might	241	bytewise/binary I/O. In future versions, enabling this option might
174	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
175	described in RFC4627.	243	described in RFC4627.
176		244
177	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
178	string as a (non-encoded) unicode string, while "decode" expects	246	string as a (non-encoded) Unicode string, while "decode" expects
179	thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or	247	thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or
180	UTF-16) needs to be done yourself, e.g. using the Encode module.	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.
181		252
182	Example, output UTF-16BE-encoded JSON:	253	Example, output UTF-16BE-encoded JSON:
183		254
184	use Encode;	255	use Encode;
185	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	256	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
204	2	275	2
205	]	276	]
206	}	277	}
207		278
208	$json = $json->indent ([$enable])	279	$json = $json->indent ([$enable])
		280	$enabled = $json->get_indent
209	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
210	multiline format as output, putting every array member or	282	multiline format as output, putting every array member or
211	object/hash key-value pair into its own line, identing them	283	object/hash key-value pair into its own line, indenting them
212	properly.	284	properly.
213		285
214	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
215	the resulting JSON text is guarenteed not to contain any "newlines".	287	the resulting JSON text is guaranteed not to contain any "newlines".
216		288
217	This setting has no effect when decoding JSON texts.	289	This setting has no effect when decoding JSON texts.
218		290
219	$json = $json->space_before ([$enable])	291	$json = $json->space_before ([$enable])
		292	$enabled = $json->get_space_before
220	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
221	an extra optional space before the ":" separating keys from values	294	an extra optional space before the ":" separating keys from values
222	in JSON objects.	295	in JSON objects.
223		296
224	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
…		…
230	Example, space_before enabled, space_after and indent disabled:	303	Example, space_before enabled, space_after and indent disabled:
231		304
232	{"key" :"value"}	305	{"key" :"value"}
233		306
234	$json = $json->space_after ([$enable])	307	$json = $json->space_after ([$enable])
		308	$enabled = $json->get_space_after
235	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
236	an extra optional space after the ":" separating keys from values in	310	an extra optional space after the ":" separating keys from values in
237	JSON objects and extra whitespace after the "," separating key-value	311	JSON objects and extra whitespace after the "," separating key-value
238	pairs and array members.	312	pairs and array members.
239		313
…		…
244		318
245	Example, space_before and indent disabled, space_after enabled:	319	Example, space_before and indent disabled, space_after enabled:
246		320
247	{"key": "value"}	321	{"key": "value"}
248		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
249	$json = $json->canonical ([$enable])	365	$json = $json->canonical ([$enable])
		366	$enabled = $json->get_canonical
250	If $enable is true (or missing), then the "encode" method will	367	If $enable is true (or missing), then the "encode" method will
251	output JSON objects by sorting their keys. This is adding a	368	output JSON objects by sorting their keys. This is adding a
252	comparatively high overhead.	369	comparatively high overhead.
253		370
254	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
255	pairs in the order Perl stores them (which will likely change	372	pairs in the order Perl stores them (which will likely change
256	between runs of the same script).	373	between runs of the same script).
257		374
258	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
259	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
260	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
261	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
262	in Perl.	379	in Perl.
263		380
264	This setting has no effect when decoding JSON texts.	381	This setting has no effect when decoding JSON texts.
265		382
		383	This setting has currently no effect on tied hashes.
		384
266	$json = $json->allow_nonref ([$enable])	385	$json = $json->allow_nonref ([$enable])
		386	$enabled = $json->get_allow_nonref
267	If $enable is true (or missing), then the "encode" method can	387	If $enable is true (or missing), then the "encode" method can
268	convert a non-reference into its corresponding string, number or	388	convert a non-reference into its corresponding string, number or
269	null JSON value, which is an extension to RFC4627. Likewise,	389	null JSON value, which is an extension to RFC4627. Likewise,
270	"decode" will accept those JSON values instead of croaking.	390	"decode" will accept those JSON values instead of croaking.
271		391
…		…
278	"allow_nonref", resulting in an invalid JSON text:	398	"allow_nonref", resulting in an invalid JSON text:
279		399
280	JSON::XS->new->allow_nonref->encode ("Hello, World!")	400	JSON::XS->new->allow_nonref->encode ("Hello, World!")
281	=> "Hello, World!"	401	=> "Hello, World!"
282		402
		403	$json = $json->allow_unknown ([$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
283	$json = $json->shrink ([$enable])	530	$json = $json->shrink ([$enable])
		531	$enabled = $json->get_shrink
284	Perl usually over-allocates memory a bit when allocating space for	532	Perl usually over-allocates memory a bit when allocating space for
285	strings. This flag optionally resizes strings generated by either	533	strings. This flag optionally resizes strings generated by either
286	"encode" or "decode" to their minimum size possible. This can save	534	"encode" or "decode" to their minimum size possible. This can save
287	memory when your JSON texts are either very very long or you have	535	memory when your JSON texts are either very very long or you have
288	many short strings. It will also try to downgrade any strings to	536	many short strings. It will also try to downgrade any strings to
…		…
306	converting strings that look like integers or floats into integers	554	converting strings that look like integers or floats into integers
307	or floats internally (there is no difference on the Perl level),	555	or floats internally (there is no difference on the Perl level),
308	saving space.	556	saving space.
309		557
310	$json = $json->max_depth ([$maximum_nesting_depth])	558	$json = $json->max_depth ([$maximum_nesting_depth])
		559	$max_depth = $json->get_max_depth
311	Sets the maximum nesting level (default 512) accepted while encoding	560	Sets the maximum nesting level (default 512) accepted while encoding
312	or decoding. If the JSON text or Perl data structure has an equal or	561	or decoding. If a higher nesting level is detected in JSON text or a
313	higher nesting level then this limit, then the encoder and decoder	562	Perl data structure, then the encoder and decoder will stop and
314	will stop and croak at that point.	563	croak at that point.
315		564
316	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
317	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
318	"{" or "[" characters without their matching closing parenthesis	567	"{" or "[" characters without their matching closing parenthesis
319	crossed to reach a given character in a string.	568	crossed to reach a given character in a string.
320		569
321	Setting the maximum depth to one disallows any nesting, so that	570	Setting the maximum depth to one disallows any nesting, so that
322	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.
323		572
324	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,
325	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).
326		593
327	See SECURITY CONSIDERATIONS, below, for more info on why this is	594	See SECURITY CONSIDERATIONS, below, for more info on why this is
328	useful.	595	useful.
329		596
330	$json_text = $json->encode ($perl_scalar)	597	$json_text = $json->encode ($perl_scalar)
…		…
355	and you need to know where the JSON text ends.	622	and you need to know where the JSON text ends.
356		623
357	JSON::XS->new->decode_prefix ("[1] the tail")	624	JSON::XS->new->decode_prefix ("[1] the tail")
358	=> ([], 3)	625	=> ([], 3)
359		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 (and can be implemented with a minimum of method
		635	calls).
		636
		637	JSON::XS will only attempt to parse the JSON text once it is sure it has
		638	enough text to get a decisive result, using a very simple but truly
		639	incremental parser. This means that it sometimes won't stop as early as
		640	the full parser, for example, it doesn't detect parenthese mismatches.
		641	The only thing it guarantees is that it starts decoding as soon as a
		642	syntactically valid JSON text has been seen. This means you need to set
		643	resource limits (e.g. "max_size") to ensure the parser will stop parsing
		644	in the presence if syntax errors.
		645
		646	The following methods implement this incremental parser.
		647
		648	[void, scalar or list context] = $json->incr_parse ([$string])
		649	This is the central parsing function. It can both append new text
		650	and extract objects from the stream accumulated so far (both of
		651	these functions are optional).
		652
		653	If $string is given, then this string is appended to the already
		654	existing JSON fragment stored in the $json object.
		655
		656	After that, if the function is called in void context, it will
		657	simply return without doing anything further. This can be used to
		658	add more text in as many chunks as you want.
		659
		660	If the method is called in scalar context, then it will try to
		661	extract exactly one JSON object. If that is successful, it will
		662	return this object, otherwise it will return "undef". If there is a
		663	parse error, this method will croak just as "decode" would do (one
		664	can then use "incr_skip" to skip the errornous part). This is the
		665	most common way of using the method.
		666
		667	And finally, in list context, it will try to extract as many objects
		668	from the stream as it can find and return them, or the empty list
		669	otherwise. For this to work, there must be no separators between the
		670	JSON objects or arrays, instead they must be concatenated
		671	back-to-back. If an error occurs, an exception will be raised as in
		672	the scalar context case. Note that in this case, any
		673	previously-parsed JSON texts will be lost.
		674
		675	$lvalue_string = $json->incr_text
		676	This method returns the currently stored JSON fragment as an lvalue,
		677	that is, you can manipulate it. This only works when a preceding
		678	call to "incr_parse" in scalar context successfully returned an
		679	object. Under all other circumstances you must not call this
		680	function (I mean it. although in simple tests it might actually
		681	work, it will fail under real world conditions). As a special
		682	exception, you can also call this method before having parsed
		683	anything.
		684
		685	This function is useful in two cases: a) finding the trailing text
		686	after a JSON object or b) parsing multiple JSON objects separated by
		687	non-JSON text (such as commas).
		688
		689	$json->incr_skip
		690	This will reset the state of the incremental parser and will remove
		691	the parsed text from the input buffer so far. This is useful after
		692	"incr_parse" died, in which case the input buffer and incremental
		693	parser state is left unchanged, to skip the text parsed so far and
		694	to reset the parse state.
		695
		696	The difference to "incr_reset" is that only text until the parse
		697	error occured is removed.
		698
		699	$json->incr_reset
		700	This completely resets the incremental parser, that is, after this
		701	call, it will be as if the parser had never parsed anything.
		702
		703	This is useful if you want to repeatedly parse JSON objects and want
		704	to ignore any trailing data, which means you have to reset the
		705	parser after each successful decode.
		706
		707	LIMITATIONS
		708	All options that affect decoding are supported, except "allow_nonref".
		709	The reason for this is that it cannot be made to work sensibly: JSON
		710	objects and arrays are self-delimited, i.e. you can concatenate them
		711	back to back and still decode them perfectly. This does not hold true
		712	for JSON numbers, however.
		713
		714	For example, is the string 1 a single JSON number, or is it simply the
		715	start of 12? Or is 12 a single JSON number, or the concatenation of 1
		716	and 2? In neither case you can tell, and this is why JSON::XS takes the
		717	conservative route and disallows this case.
		718
		719	EXAMPLES
		720	Some examples will make all this clearer. First, a simple example that
		721	works similarly to "decode_prefix": We want to decode the JSON object at
		722	the start of a string and identify the portion after the JSON object:
		723
		724	my $text = "[1,2,3] hello";
		725
		726	my $json = new JSON::XS;
		727
		728	my $obj = $json->incr_parse ($text)
		729	or die "expected JSON object or array at beginning of string";
		730
		731	my $tail = $json->incr_text;
		732	# $tail now contains " hello"
		733
		734	Easy, isn't it?
		735
		736	Now for a more complicated example: Imagine a hypothetical protocol
		737	where you read some requests from a TCP stream, and each request is a
		738	JSON array, without any separation between them (in fact, it is often
		739	useful to use newlines as "separators", as these get interpreted as
		740	whitespace at the start of the JSON text, which makes it possible to
		741	test said protocol with "telnet"...).
		742
		743	Here is how you'd do it (it is trivial to write this in an event-based
		744	manner):
		745
		746	my $json = new JSON::XS;
		747
		748	# read some data from the socket
		749	while (sysread $socket, my $buf, 4096) {
		750
		751	# split and decode as many requests as possible
		752	for my $request ($json->incr_parse ($buf)) {
		753	# act on the $request
		754	}
		755	}
		756
		757	Another complicated example: Assume you have a string with JSON objects
		758	or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
		759	[3]"). To parse them, we have to skip the commas between the JSON texts,
		760	and here is where the lvalue-ness of "incr_text" comes in useful:
		761
		762	my $text = "[1],[2], [3]";
		763	my $json = new JSON::XS;
		764
		765	# void context, so no parsing done
		766	$json->incr_parse ($text);
		767
		768	# now extract as many objects as possible. note the
		769	# use of scalar context so incr_text can be called.
		770	while (my $obj = $json->incr_parse) {
		771	# do something with $obj
		772
		773	# now skip the optional comma
		774	$json->incr_text =~ s/^ \s* , //x;
		775	}
		776
		777	Now lets go for a very complex example: Assume that you have a gigantic
		778	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		779	but you cannot load it into memory fully (this has actually happened in
		780	the real world :).
		781
		782	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		783	can still help you: You implement a (very simple) array parser and let
		784	JSON decode the array elements, which are all full JSON objects on their
		785	own (this wouldn't work if the array elements could be JSON numbers, for
		786	example):
		787
		788	my $json = new JSON::XS;
		789
		790	# open the monster
		791	open my $fh, "<bigfile.json"
		792	or die "bigfile: $!";
		793
		794	# first parse the initial "["
		795	for (;;) {
		796	sysread $fh, my $buf, 65536
		797	or die "read error: $!";
		798	$json->incr_parse ($buf); # void context, so no parsing
		799
		800	# Exit the loop once we found and removed(!) the initial "[".
		801	# In essence, we are (ab-)using the $json object as a simple scalar
		802	# we append data to.
		803	last if $json->incr_text =~ s/^ \s* \[ //x;
		804	}
		805
		806	# now we have the skipped the initial "[", so continue
		807	# parsing all the elements.
		808	for (;;) {
		809	# in this loop we read data until we got a single JSON object
		810	for (;;) {
		811	if (my $obj = $json->incr_parse) {
		812	# do something with $obj
		813	last;
		814	}
		815
		816	# add more data
		817	sysread $fh, my $buf, 65536
		818	or die "read error: $!";
		819	$json->incr_parse ($buf); # void context, so no parsing
		820	}
		821
		822	# in this loop we read data until we either found and parsed the
		823	# separating "," between elements, or the final "]"
		824	for (;;) {
		825	# first skip whitespace
		826	$json->incr_text =~ s/^\s*//;
		827
		828	# if we find "]", we are done
		829	if ($json->incr_text =~ s/^\]//) {
		830	print "finished.\n";
		831	exit;
		832	}
		833
		834	# if we find ",", we can continue with the next element
		835	if ($json->incr_text =~ s/^,//) {
		836	last;
		837	}
		838
		839	# if we find anything else, we have a parse error!
		840	if (length $json->incr_text) {
		841	die "parse error near ", $json->incr_text;
		842	}
		843
		844	# else add more data
		845	sysread $fh, my $buf, 65536
		846	or die "read error: $!";
		847	$json->incr_parse ($buf); # void context, so no parsing
		848	}
		849
		850	This is a complex example, but most of the complexity comes from the
		851	fact that we are trying to be correct (bear with me if I am wrong, I
		852	never ran the above example :).
		853
360	MAPPING	854	MAPPING
361	This section describes how JSON::XS maps Perl values to JSON values and	855	This section describes how JSON::XS maps Perl values to JSON values and
362	vice versa. These mappings are designed to "do the right thing" in most	856	vice versa. These mappings are designed to "do the right thing" in most
363	circumstances automatically, preserving round-tripping characteristics	857	circumstances automatically, preserving round-tripping characteristics
364	(what you put in comes out as something equivalent).	858	(what you put in comes out as something equivalent).
365		859
366	For the more enlightened: note that in the following descriptions,	860	For the more enlightened: note that in the following descriptions,
367	lowercase perl refers to the Perl interpreter, while uppcercase Perl	861	lowercase perl refers to the Perl interpreter, while uppercase Perl
368	refers to the abstract Perl language itself.	862	refers to the abstract Perl language itself.
369		863
370	JSON -> PERL	864	JSON -> PERL
371	object	865	object
372	A JSON object becomes a reference to a hash in Perl. No ordering of	866	A JSON object becomes a reference to a hash in Perl. No ordering of
373	object keys is preserved (JSON does not preserver object key	867	object keys is preserved (JSON does not preserve object key ordering
374	ordering itself).	868	itself).
375		869
376	array	870	array
377	A JSON array becomes a reference to an array in Perl.	871	A JSON array becomes a reference to an array in Perl.
378		872
379	string	873	string
380	A JSON string becomes a string scalar in Perl - Unicode codepoints	874	A JSON string becomes a string scalar in Perl - Unicode codepoints
381	in JSON are represented by the same codepoints in the Perl string,	875	in JSON are represented by the same codepoints in the Perl string,
382	so no manual decoding is necessary.	876	so no manual decoding is necessary.
383		877
384	number	878	number
385	A JSON number becomes either an integer or numeric (floating point)	879	A JSON number becomes either an integer, numeric (floating point) or
386	scalar in perl, depending on its range and any fractional parts. On	880	string scalar in perl, depending on its range and any fractional
387	the Perl level, there is no difference between those as Perl handles	881	parts. On the Perl level, there is no difference between those as
388	all the conversion details, but an integer may take slightly less	882	Perl handles all the conversion details, but an integer may take
389	memory and might represent more values exactly than (floating point)	883	slightly less memory and might represent more values exactly than
		884	floating point numbers.
		885
		886	If the number consists of digits only, JSON::XS will try to
		887	represent it as an integer value. If that fails, it will try to
		888	represent it as a numeric (floating point) value if that is possible
		889	without loss of precision. Otherwise it will preserve the number as
		890	a string value (in which case you lose roundtripping ability, as the
		891	JSON number will be re-encoded toa JSON string).
		892
		893	Numbers containing a fractional or exponential part will always be
		894	represented as numeric (floating point) values, possibly at a loss
		895	of precision (in which case you might lose perfect roundtripping
		896	ability, but the JSON number will still be re-encoded as a JSON
390	numbers.	897	number).
391		898
392	true, false	899	true, false
393	These JSON atoms become "JSON::XS::true" and "JSON::XS::false",	900	These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
394	respectively. They are overloaded to act almost exactly like the	901	respectively. They are overloaded to act almost exactly like the
395	numbers 1 and 0. You can check wether a scalar is a JSON boolean by	902	numbers 1 and 0. You can check whether a scalar is a JSON boolean by
396	using the "JSON::XS::is_bool" function.	903	using the "JSON::XS::is_bool" function.
397		904
398	null	905	null
399	A JSON null atom becomes "undef" in Perl.	906	A JSON null atom becomes "undef" in Perl.
400		907
…		…
423	an exception to be thrown, except for references to the integers 0	930	an exception to be thrown, except for references to the integers 0
424	and 1, which get turned into "false" and "true" atoms in JSON. You	931	and 1, which get turned into "false" and "true" atoms in JSON. You
425	can also use "JSON::XS::false" and "JSON::XS::true" to improve	932	can also use "JSON::XS::false" and "JSON::XS::true" to improve
426	readability.	933	readability.
427		934
428	to_json [\0,JSON::XS::true] # yields [false,true]	935	encode_json [\0, JSON::XS::true] # yields [false,true]
429		936
430	JSON::XS::true, JSON::XS::false	937	JSON::XS::true, JSON::XS::false
431	These special values become JSON true and JSON false values,	938	These special values become JSON true and JSON false values,
432	respectively. You cna alos use "\1" and "\0" directly if you want.	939	respectively. You can also use "\1" and "\0" directly if you want.
433		940
434	blessed objects	941	blessed objects
435	Blessed objects are not allowed. JSON::XS currently tries to encode	942	Blessed objects are not directly representable in JSON. See the
436	their underlying representation (hash- or arrayref), but this	943	"allow_blessed" and "convert_blessed" methods on various options on
437	behaviour might change in future versions.	944	how to deal with this: basically, you can choose between throwing an
		945	exception, encoding the reference as if it weren't blessed, or
		946	provide your own serialiser method.
438		947
439	simple scalars	948	simple scalars
440	Simple Perl scalars (any scalar that is not a reference) are the	949	Simple Perl scalars (any scalar that is not a reference) are the
441	most difficult objects to encode: JSON::XS will encode undefined	950	most difficult objects to encode: JSON::XS will encode undefined
442	scalars as JSON null value, scalars that have last been used in a	951	scalars as JSON "null" values, scalars that have last been used in a
443	string context before encoding as JSON strings and anything else as	952	string context before encoding as JSON strings, and anything else as
444	number value:	953	number value:
445		954
446	# dump as number	955	# dump as number
447	to_json [2] # yields [2]	956	encode_json [2] # yields [2]
448	to_json [-3.0e17] # yields [-3e+17]	957	encode_json [-3.0e17] # yields [-3e+17]
449	my $value = 5; to_json [$value] # yields [5]	958	my $value = 5; encode_json [$value] # yields [5]
450		959
451	# used as string, so dump as string	960	# used as string, so dump as string
452	print $value;	961	print $value;
453	to_json [$value] # yields ["5"]	962	encode_json [$value] # yields ["5"]
454		963
455	# undef becomes null	964	# undef becomes null
456	to_json [undef] # yields [null]	965	encode_json [undef] # yields [null]
457		966
458	You can force the type to be a string by stringifying it:	967	You can force the type to be a JSON string by stringifying it:
459		968
460	my $x = 3.1; # some variable containing a number	969	my $x = 3.1; # some variable containing a number
461	"$x"; # stringified	970	"$x"; # stringified
462	$x .= ""; # another, more awkward way to stringify	971	$x .= ""; # another, more awkward way to stringify
463	print $x; # perl does it for you, too, quite often	972	print $x; # perl does it for you, too, quite often
464		973
465	You can force the type to be a number by numifying it:	974	You can force the type to be a JSON number by numifying it:
466		975
467	my $x = "3"; # some variable containing a string	976	my $x = "3"; # some variable containing a string
468	$x += 0; # numify it, ensuring it will be dumped as a number	977	$x += 0; # numify it, ensuring it will be dumped as a number
469	$x *= 1; # same thing, the choise is yours.	978	$x *= 1; # same thing, the choice is yours.
470		979
471	You can not currently output JSON booleans or force the type in	980	You can not currently force the type in other, less obscure, ways.
472	other, less obscure, ways. Tell me if you need this capability.	981	Tell me if you need this capability (but don't forget to explain why
		982	it's needed :).
473		983
474	COMPARISON	984	ENCODING/CODESET FLAG NOTES
475	As already mentioned, this module was created because none of the	985	The interested reader might have seen a number of flags that signify
476	existing JSON modules could be made to work correctly. First I will	986	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
477	describe the problems (or pleasures) I encountered with various existing	987	some confusion on what these do, so here is a short comparison:
478	JSON modules, followed by some benchmark values. JSON::XS was designed
479	not to suffer from any of these problems or limitations.
480		988
481	JSON 1.07	989	"utf8" controls whether the JSON text created by "encode" (and expected
482	Slow (but very portable, as it is written in pure Perl).	990	by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
		991	control whether "encode" escapes character values outside their
		992	respective codeset range. Neither of these flags conflict with each
		993	other, although some combinations make less sense than others.
483		994
484	Undocumented/buggy Unicode handling (how JSON handles unicode values	995	Care has been taken to make all flags symmetrical with respect to
485	is undocumented. One can get far by feeding it unicode strings and	996	"encode" and "decode", that is, texts encoded with any combination of
486	doing en-/decoding oneself, but unicode escapes are not working	997	these flag values will be correctly decoded when the same flags are used
		998	- in general, if you use different flag settings while encoding vs. when
		999	decoding you likely have a bug somewhere.
		1000
		1001	Below comes a verbose discussion of these flags. Note that a "codeset"
		1002	is simply an abstract set of character-codepoint pairs, while an
		1003	encoding takes those codepoint numbers and encodes them, in our case
		1004	into octets. Unicode is (among other things) a codeset, UTF-8 is an
		1005	encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets and
		1006	encodings at the same time, which can be confusing.
		1007
		1008	"utf8" flag disabled
		1009	When "utf8" is disabled (the default), then "encode"/"decode"
		1010	generate and expect Unicode strings, that is, characters with high
		1011	ordinal Unicode values (> 255) will be encoded as such characters,
		1012	and likewise such characters are decoded as-is, no canges to them
		1013	will be done, except "(re-)interpreting" them as Unicode codepoints
		1014	or Unicode characters, respectively (to Perl, these are the same
		1015	thing in strings unless you do funny/weird/dumb stuff).
		1016
		1017	This is useful when you want to do the encoding yourself (e.g. when
		1018	you want to have UTF-16 encoded JSON texts) or when some other layer
		1019	does the encoding for you (for example, when printing to a terminal
		1020	using a filehandle that transparently encodes to UTF-8 you certainly
		1021	do NOT want to UTF-8 encode your data first and have Perl encode it
		1022	another time).
		1023
		1024	"utf8" flag enabled
		1025	If the "utf8"-flag is enabled, "encode"/"decode" will encode all
		1026	characters using the corresponding UTF-8 multi-byte sequence, and
		1027	will expect your input strings to be encoded as UTF-8, that is, no
		1028	"character" of the input string must have any value > 255, as UTF-8
		1029	does not allow that.
		1030
		1031	The "utf8" flag therefore switches between two modes: disabled means
		1032	you will get a Unicode string in Perl, enabled means you get an
		1033	UTF-8 encoded octet/binary string in Perl.
		1034
		1035	"latin1" or "ascii" flags enabled
		1036	With "latin1" (or "ascii") enabled, "encode" will escape characters
		1037	with ordinal values > 255 (> 127 with "ascii") and encode the
		1038	remaining characters as specified by the "utf8" flag.
		1039
		1040	If "utf8" is disabled, then the result is also correctly encoded in
		1041	those character sets (as both are proper subsets of Unicode, meaning
		1042	that a Unicode string with all character values < 256 is the same
		1043	thing as a ISO-8859-1 string, and a Unicode string with all
		1044	character values < 128 is the same thing as an ASCII string in
487	properly).	1045	Perl).
488		1046
489	No roundtripping (strings get clobbered if they look like numbers,	1047	If "utf8" is enabled, you still get a correct UTF-8-encoded string,
490	e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that	1048	regardless of these flags, just some more characters will be escaped
491	will decode into the number 2.	1049	using "\uXXXX" then before.
492		1050
493	JSON::PC 0.01	1051	Note that ISO-8859-1-encoded strings are not compatible with UTF-8
494	Very fast.	1052	encoding, while ASCII-encoded strings are. That is because the
		1053	ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
		1054	codeset being a subset of Unicode), while ASCII is.
495		1055
496	Undocumented/buggy Unicode handling.	1056	Surprisingly, "decode" will ignore these flags and so treat all
		1057	input values as governed by the "utf8" flag. If it is disabled, this
		1058	allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
		1059	strict subsets of Unicode. If it is enabled, you can correctly
		1060	decode UTF-8 encoded strings.
497		1061
498	No roundtripping.	1062	So neither "latin1" nor "ascii" are incompatible with the "utf8"
		1063	flag - they only govern when the JSON output engine escapes a
		1064	character or not.
499		1065
500	Has problems handling many Perl values (e.g. regex results and other	1066	The main use for "latin1" is to relatively efficiently store binary
501	magic values will make it croak).	1067	data as JSON, at the expense of breaking compatibility with most
		1068	JSON decoders.
502		1069
503	Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"	1070	The main use for "ascii" is to force the output to not contain
504	which is not a valid JSON text.	1071	characters with values > 127, which means you can interpret the
		1072	resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
		1073	any character set and 8-bit-encoding, and still get the same data
		1074	structure back. This is useful when your channel for JSON transfer
		1075	is not 8-bit clean or the encoding might be mangled in between (e.g.
		1076	in mail), and works because ASCII is a proper subset of most 8-bit
		1077	and multibyte encodings in use in the world.
505		1078
506	Unmaintained (maintainer unresponsive for many months, bugs are not	1079	JSON and ECMAscript
507	getting fixed).	1080	JSON syntax is based on how literals are represented in javascript (the
		1081	not-standardised predecessor of ECMAscript) which is presumably why it
		1082	is called "JavaScript Object Notation".
508		1083
509	JSON::Syck 0.21	1084	However, JSON is not a subset (and also not a superset of course) of
510	Very buggy (often crashes).	1085	ECMAscript (the standard) or javascript (whatever browsers actually
		1086	implement).
511		1087
512	Very inflexible (no human-readable format supported, format pretty	1088	If you want to use javascript's "eval" function to "parse" JSON, you
513	much undocumented. I need at least a format for easy reading by	1089	might run into parse errors for valid JSON texts, or the resulting data
514	humans and a single-line compact format for use in a protocol, and	1090	structure might not be queryable:
515	preferably a way to generate ASCII-only JSON texts).
516		1091
517	Completely broken (and confusingly documented) Unicode handling	1092	One of the problems is that U+2028 and U+2029 are valid characters
518	(unicode escapes are not working properly, you need to set	1093	inside JSON strings, but are not allowed in ECMAscript string literals,
519	ImplicitUnicode to different values on en- and decoding to get	1094	so the following Perl fragment will not output something that can be
520	symmetric behaviour).	1095	guaranteed to be parsable by javascript's "eval":
521		1096
522	No roundtripping (simple cases work, but this depends on wether the	1097	use JSON::XS;
523	scalar value was used in a numeric context or not).
524		1098
525	Dumping hashes may skip hash values depending on iterator state.	1099	print encode_json [chr 0x2028];
526		1100
527	Unmaintained (maintainer unresponsive for many months, bugs are not	1101	The right fix for this is to use a proper JSON parser in your javascript
528	getting fixed).	1102	programs, and not rely on "eval" (see for example Douglas Crockford's
		1103	json2.js parser).
529		1104
530	Does not check input for validity (i.e. will accept non-JSON input	1105	If this is not an option, you can, as a stop-gap measure, simply encode
531	and return "something" instead of raising an exception. This is a	1106	to ASCII-only JSON:
532	security issue: imagine two banks transfering money between each
533	other using JSON. One bank might parse a given non-JSON request and
534	deduct money, while the other might reject the transaction with a
535	syntax error. While a good protocol will at least recover, that is
536	extra unnecessary work and the transaction will still not succeed).
537		1107
538	JSON::DWIW 0.04	1108	use JSON::XS;
539	Very fast. Very natural. Very nice.
540		1109
541	Undocumented unicode handling (but the best of the pack. Unicode	1110	print JSON::XS->new->ascii->encode ([chr 0x2028]);
542	escapes still don't get parsed properly).
543		1111
544	Very inflexible.	1112	Note that this will enlarge the resulting JSON text quite a bit if you
		1113	have many non-ASCII characters. You might be tempted to run some regexes
		1114	to only escape U+2028 and U+2029, e.g.:
545		1115
546	No roundtripping.	1116	# DO NOT USE THIS!
		1117	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1118	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1119	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1120	print $json;
547		1121
548	Does not generate valid JSON texts (key strings are often unquoted,	1122	Note that this is a bad idea: the above only works for U+2028 and
549	empty keys result in nothing being output)	1123	U+2029 and thus only for fully ECMAscript-compliant parsers. Many
		1124	existing javascript implementations, however, have issues with other
		1125	characters as well - using "eval" naively simply will cause problems.
550		1126
551	Does not check input for validity.	1127	Another problem is that some javascript implementations reserve some
		1128	property names for their own purposes (which probably makes them
		1129	non-ECMAscript-compliant). For example, Iceweasel reserves the
		1130	"__proto__" property name for it's own purposes.
		1131
		1132	If that is a problem, you could parse try to filter the resulting JSON
		1133	output for these property strings, e.g.:
		1134
		1135	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1136
		1137	This works because "__proto__" is not valid outside of strings, so every
		1138	occurence of ""__proto__"\s*:" must be a string used as property name.
		1139
		1140	If you know of other incompatibilities, please let me know.
552		1141
553	JSON and YAML	1142	JSON and YAML
554	You often hear that JSON is a subset (or a close subset) of YAML. This	1143	You often hear that JSON is a subset of YAML. This is, however, a mass
555	is, however, a mass hysteria and very far from the truth. In general,	1144	hysteria(*) and very far from the truth (as of the time of this
556	there is no way to configure JSON::XS to output a data structure as	1145	writing), so let me state it clearly: *in general, there is no way to
557	valid YAML.	1146	configure JSON::XS to output a data structure as valid YAML* that works
		1147	in all cases.
558		1148
559	If you really must use JSON::XS to generate YAML, you should use this	1149	If you really must use JSON::XS to generate YAML, you should use this
560	algorithm (subject to change in future versions):	1150	algorithm (subject to change in future versions):
561		1151
562	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1152	my $to_yaml = JSON::XS->new->utf8->space_after (1);
563	my $yaml = $to_yaml->encode ($ref) . "\n";	1153	my $yaml = $to_yaml->encode ($ref) . "\n";
564		1154
565	This will usually generate JSON texts that also parse as valid YAML.	1155	This will usually generate JSON texts that also parse as valid YAML.
566	Please note that YAML has hardcoded limits on (simple) object key	1156	Please note that YAML has hardcoded limits on (simple) object key
567	lengths that JSON doesn't have, so you should make sure that your hash	1157	lengths that JSON doesn't have and also has different and incompatible
		1158	unicode character escape syntax, so you should make sure that your hash
568	keys are noticably shorter than the 1024 characters YAML allows.	1159	keys are noticeably shorter than the 1024 "stream characters" YAML
		1160	allows and that you do not have characters with codepoint values outside
		1161	the Unicode BMP (basic multilingual page). YAML also does not allow "\/"
		1162	sequences in strings (which JSON::XS does not currently generate, but
		1163	other JSON generators might).
569		1164
570	There might be other incompatibilities that I am not aware of. In	1165	There might be other incompatibilities that I am not aware of (or the
		1166	YAML specification has been changed yet again - it does so quite often).
571	general you should not try to generate YAML with a JSON generator or	1167	In general you should not try to generate YAML with a JSON generator or
572	vice versa, or try to parse JSON with a YAML parser or vice versa:	1168	vice versa, or try to parse JSON with a YAML parser or vice versa:
573	chances are high that you will run into severe interoperability	1169	chances are high that you will run into severe interoperability problems
574	problems.	1170	when you least expect it.
		1171
		1172	(*) I have been pressured multiple times by Brian Ingerson (one of the
		1173	authors of the YAML specification) to remove this paragraph, despite
		1174	him acknowledging that the actual incompatibilities exist. As I was
		1175	personally bitten by this "JSON is YAML" lie, I refused and said I
		1176	will continue to educate people about these issues, so others do not
		1177	run into the same problem again and again. After this, Brian called
		1178	me a (quote)complete and worthless idiot(unquote).
		1179
		1180	In my opinion, instead of pressuring and insulting people who
		1181	actually clarify issues with YAML and the wrong statements of some
		1182	of its proponents, I would kindly suggest reading the JSON spec
		1183	(which is not that difficult or long) and finally make YAML
		1184	compatible to it, and educating users about the changes, instead of
		1185	spreading lies about the real compatibility for many years and
		1186	trying to silence people who point out that it isn't true.
		1187
		1188	Addendum/2009: the YAML 1.2 spec is still incomaptible with JSON,
		1189	even though the incompatibilities have been documented (and are
		1190	known to Brian) for many years and the spec makes explicit claims
		1191	that YAML is a superset of JSON. It would be so easy to fix, but
		1192	apparently, bullying and corrupting userdata is so much easier.
575		1193
576	SPEED	1194	SPEED
577	It seems that JSON::XS is surprisingly fast, as shown in the following	1195	It seems that JSON::XS is surprisingly fast, as shown in the following
578	tables. They have been generated with the help of the "eg/bench" program	1196	tables. They have been generated with the help of the "eg/bench" program
579	in the JSON::XS distribution, to make it easy to compare on your own	1197	in the JSON::XS distribution, to make it easy to compare on your own
580	system.	1198	system.
581		1199
582	First comes a comparison between various modules using a very short	1200	First comes a comparison between various modules using a very short
583	single-line JSON string:	1201	single-line JSON string (also available at
		1202	<http://dist.schmorp.de/misc/json/short.json>).
584		1203
585	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1204	{"method": "handleMessage", "params": ["user1",
586	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1205	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1206	1, 0]}
587		1207
588	It shows the number of encodes/decodes per second (JSON::XS uses the	1208	It shows the number of encodes/decodes per second (JSON::XS uses the
589	functional interface, while JSON::XS/2 uses the OO interface with	1209	functional interface, while JSON::XS/2 uses the OO interface with
590	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).	1210	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink.
591	Higher is better:	1211	JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses
		1212	the from_json method). Higher is better:
592		1213
593	module \| encode \| decode \|	1214	module \| encode \| decode \|
594	-----------\|------------\|------------\|	1215	--------------\|------------\|------------\|
595	JSON \| 7645.468 \| 4208.613 \|	1216	JSON::DWIW/DS \| 86302.551 \| 102300.098 \|
596	JSON::DWIW \| 40721.398 \| 77101.176 \|	1217	JSON::DWIW/FJ \| 86302.551 \| 75983.768 \|
597	JSON::PC \| 65948.176 \| 78251.940 \|	1218	JSON::PP \| 15827.562 \| 6638.658 \|
598	JSON::Syck \| 22844.793 \| 26479.192 \|	1219	JSON::Syck \| 63358.066 \| 47662.545 \|
599	JSON::XS \| 388361.481 \| 199728.762 \|	1220	JSON::XS \| 511500.488 \| 511500.488 \|
600	JSON::XS/2 \| 218453.333 \| 192399.266 \|	1221	JSON::XS/2 \| 291271.111 \| 388361.481 \|
601	JSON::XS/3 \| 338250.323 \| 192399.266 \|	1222	JSON::XS/3 \| 361577.931 \| 361577.931 \|
602	Storable \| 15779.925 \| 14169.946 \|	1223	Storable \| 66788.280 \| 265462.278 \|
603	-----------+------------+------------+	1224	--------------+------------+------------+
604		1225
605	That is, JSON::XS is about five times faster than JSON::DWIW on	1226	That is, JSON::XS is almost six times faster than JSON::DWIW on
606	encoding, about three times faster on decoding, and over fourty times	1227	encoding, about five times faster on decoding, and over thirty to
607	faster than JSON, even with pretty-printing and key sorting. It also	1228	seventy times faster than JSON's pure perl implementation. It also
608	compares favourably to Storable for small amounts of data.	1229	compares favourably to Storable for small amounts of data.
609		1230
610	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1231	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
611	search API (http://nanoref.com/yahooapis/mgPdGg):	1232	search API (<http://dist.schmorp.de/misc/json/long.json>).
612		1233
613	module \| encode \| decode \|	1234	module \| encode \| decode \|
614	-----------\|------------\|------------\|	1235	--------------\|------------\|------------\|
		1236	JSON::DWIW/DS \| 1647.927 \| 2673.916 \|
		1237	JSON::DWIW/FJ \| 1630.249 \| 2596.128 \|
615	JSON \| 254.685 \| 37.665 \|	1238	JSON::PP \| 400.640 \| 62.311 \|
616	JSON::DWIW \| 843.343 \| 1049.731 \|	1239	JSON::Syck \| 1481.040 \| 1524.869 \|
617	JSON::PC \| 3602.116 \| 2307.352 \|	1240	JSON::XS \| 20661.596 \| 9541.183 \|
618	JSON::Syck \| 505.107 \| 787.899 \|	1241	JSON::XS/2 \| 10683.403 \| 9416.938 \|
619	JSON::XS \| 5747.196 \| 3690.220 \|	1242	JSON::XS/3 \| 20661.596 \| 9400.054 \|
620	JSON::XS/2 \| 3968.121 \| 3676.634 \|	1243	Storable \| 19765.806 \| 10000.725 \|
621	JSON::XS/3 \| 6105.246 \| 3662.508 \|
622	Storable \| 4417.337 \| 5285.161 \|
623	-----------+------------+------------+	1244	--------------+------------+------------+
624		1245
625	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1246	Again, JSON::XS leads by far (except for Storable which non-surprisingly
626	decodes faster).	1247	decodes a bit faster).
627		1248
628	On large strings containing lots of high unicode characters, some	1249	On large strings containing lots of high Unicode characters, some
629	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the	1250	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
630	result will be broken due to missing (or wrong) unicode handling. Others	1251	result will be broken due to missing (or wrong) Unicode handling. Others
631	refuse to decode or encode properly, so it was impossible to prepare a	1252	refuse to decode or encode properly, so it was impossible to prepare a
632	fair comparison table for that case.	1253	fair comparison table for that case.
633		1254
634	SECURITY CONSIDERATIONS	1255	SECURITY CONSIDERATIONS
635	When you are using JSON in a protocol, talking to untrusted potentially	1256	When you are using JSON in a protocol, talking to untrusted potentially
…		…
639	have any buffer overflows. Obviously, this module should ensure that and	1260	have any buffer overflows. Obviously, this module should ensure that and
640	I am trying hard on making that true, but you never know.	1261	I am trying hard on making that true, but you never know.
641		1262
642	Second, you need to avoid resource-starving attacks. That means you	1263	Second, you need to avoid resource-starving attacks. That means you
643	should limit the size of JSON texts you accept, or make sure then when	1264	should limit the size of JSON texts you accept, or make sure then when
644	your resources run out, thats just fine (e.g. by using a separate	1265	your resources run out, that's just fine (e.g. by using a separate
645	process that can crash safely). The size of a JSON text in octets or	1266	process that can crash safely). The size of a JSON text in octets or
646	characters is usually a good indication of the size of the resources	1267	characters is usually a good indication of the size of the resources
647	required to decode it into a Perl structure.	1268	required to decode it into a Perl structure. While JSON::XS can check
		1269	the size of the JSON text, it might be too late when you already have it
		1270	in memory, so you might want to check the size before you accept the
		1271	string.
648		1272
649	Third, JSON::XS recurses using the C stack when decoding objects and	1273	Third, JSON::XS recurses using the C stack when decoding objects and
650	arrays. The C stack is a limited resource: for instance, on my amd64	1274	arrays. The C stack is a limited resource: for instance, on my amd64
651	machine with 8MB of stack size I can decode around 180k nested arrays	1275	machine with 8MB of stack size I can decode around 180k nested arrays
652	but only 14k nested JSON objects (due to perl itself recursing deeply on	1276	but only 14k nested JSON objects (due to perl itself recursing deeply on
653	croak to free the temporary). If that is exceeded, the program crashes.	1277	croak to free the temporary). If that is exceeded, the program crashes.
654	to be conservative, the default nesting limit is set to 512. If your	1278	To be conservative, the default nesting limit is set to 512. If your
655	process has a smaller stack, you should adjust this setting accordingly	1279	process has a smaller stack, you should adjust this setting accordingly
656	with the "max_depth" method.	1280	with the "max_depth" method.
657		1281
658	And last but least, something else could bomb you that I forgot to think	1282	Something else could bomb you, too, that I forgot to think of. In that
659	of. In that case, you get to keep the pieces. I am always open for	1283	case, you get to keep the pieces. I am always open for hints, though...
660	hints, though...
661		1284
		1285	Also keep in mind that JSON::XS might leak contents of your Perl data
		1286	structures in its error messages, so when you serialise sensitive
		1287	information you might want to make sure that exceptions thrown by
		1288	JSON::XS will not end up in front of untrusted eyes.
		1289
662	If you are using JSON::XS to return packets to consumption by javascript	1290	If you are using JSON::XS to return packets to consumption by JavaScript
663	scripts in a browser you should have a look at	1291	scripts in a browser you should have a look at
664	<http://jpsykes.com/47/practical-csrf-and-json-security> to see wether	1292	<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/>
665	you are vulnerable to some common attack vectors (which really are	1293	to see whether you are vulnerable to some common attack vectors (which
666	browser design bugs, but it is still you who will have to deal with it,	1294	really are browser design bugs, but it is still you who will have to
667	as major browser developers care only for features, not about doing	1295	deal with it, as major browser developers care only for features, not
668	security right).	1296	about getting security right).
		1297
		1298	THREADS
		1299	This module is not guaranteed to be thread safe and there are no plans
		1300	to change this until Perl gets thread support (as opposed to the
		1301	horribly slow so-called "threads" which are simply slow and bloated
		1302	process simulations - use fork, it's much faster, cheaper, better).
		1303
		1304	(It might actually work, but you have been warned).
669		1305
670	BUGS	1306	BUGS
671	While the goal of this module is to be correct, that unfortunately does	1307	While the goal of this module is to be correct, that unfortunately does
672	not mean its bug-free, only that I think its design is bug-free. It is	1308	not mean it's bug-free, only that I think its design is bug-free. If you
673	still relatively early in its development. If you keep reporting bugs
674	they will be fixed swiftly, though.	1309	keep reporting bugs they will be fixed swiftly, though.
		1310
		1311	Please refrain from using rt.cpan.org or any other bug reporting
		1312	service. I put the contact address into my modules for a reason.
		1313
		1314	SEE ALSO
		1315	The json_xs command line utility for quick experiments.
675		1316
676	AUTHOR	1317	AUTHOR
677	Marc Lehmann <schmorp@schmorp.de>	1318	Marc Lehmann <schmorp@schmorp.de>
678	http://home.schmorp.de/	1319	http://home.schmorp.de/
679		1320

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Comparing JSON-XS/README (file contents): Revision 1.14 by root, Sat Jun 23 23:50:03 2007 UTC vs. Revision 1.34 by root, Thu Mar 11 17:36:09 2010 UTC

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Comparing JSON-XS/README (file contents):
Revision 1.14 by root, Sat Jun 23 23:50:03 2007 UTC vs.
Revision 1.34 by root, Thu Mar 11 17:36:09 2010 UTC