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

Comparing JSON-XS/README (file contents):
Revision 1.15 by root, Mon Jul 2 08:06:48 2007 UTC vs.
Revision 1.24 by root, Thu Mar 27 06:37:35 2008 UTC

…		…
1	NAME	1	NAME
2	JSON::XS - JSON serialising/deserialising, done correctly and fast	2	JSON::XS - JSON serialising/deserialising, done correctly and fast
3		3
		4	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
		5	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
		6
4	SYNOPSIS	7	SYNOPSIS
5	use JSON::XS;	8	use JSON::XS;
6		9
7	# exported functions, they croak on error	10	# exported functions, they croak on error
8	# and expect/generate UTF-8	11	# and expect/generate UTF-8
9		12
10	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	13	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
11	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	14	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
12		15
13	# OO-interface	16	# OO-interface
14		17
15	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	18	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
16	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	19	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
17	$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.
18		29
19	DESCRIPTION	30	DESCRIPTION
20	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
21	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.
22	To reach the latter goal it was written in C.	33	To reach the latter goal it was written in C.
		34
		35	Beginning with version 2.0 of the JSON module, when both JSON and
		36	JSON::XS are installed, then JSON will fall back on JSON::XS (this can
		37	be overriden) with no overhead due to emulation (by inheritign
		38	constructor and methods). If JSON::XS is not available, it will fall
		39	back to the compatible JSON::PP module as backend, so using JSON instead
		40	of JSON::XS gives you a portable JSON API that can be fast when you need
		41	and doesn't require a C compiler when that is a problem.
23		42
24	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
25	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
26	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
27	cases their maintainers are unresponsive, gone missing, or not listening	46	cases their maintainers are unresponsive, gone missing, or not listening
31		50
32	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
33	vice versa.	52	vice versa.
34		53
35	FEATURES	54	FEATURES
36	* correct unicode handling	55	* correct Unicode handling
		56
37	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
38	when it does so.	58	does so, and even documents what "correct" means.
39		59
40	* round-trip integrity	60	* round-trip integrity
		61
41	When you serialise a perl data structure using only datatypes	62	When you serialise a perl data structure using only datatypes
42	supported by JSON, the deserialised data structure is identical on	63	supported by JSON, the deserialised data structure is identical on
43	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"
44	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.
45		67
46	* strict checking of JSON correctness	68	* strict checking of JSON correctness
		69
47	There is no guessing, no generating of illegal JSON texts by	70	There is no guessing, no generating of illegal JSON texts by
48	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
49	is a security feature).	72	is a security feature).
50		73
51	* fast	74	* fast
52	Compared to other JSON modules, this module compares favourably in
53	terms of speed, too.
54		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
55	* simple to use	80	* simple to use
		81
56	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
57	interface.	83	objetc oriented interface interface.
58		84
59	* reasonably versatile output formats	85	* reasonably versatile output formats
		86
60	You can choose between the most compact guarenteed single-line	87	You can choose between the most compact guaranteed-single-line
61	format possible (nice for simple line-based protocols), a pure-ascii	88	format possible (nice for simple line-based protocols), a pure-ascii
62	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
63	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
64	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
65	whatever way you like.	92	whatever way you like.
66		93
67	FUNCTIONAL INTERFACE	94	FUNCTIONAL INTERFACE
68	The following convinience methods are provided by this module. They are	95	The following convenience methods are provided by this module. They are
69	exported by default:	96	exported by default:
70		97
71	$json_text = to_json $perl_scalar	98	$json_text = encode_json $perl_scalar
72	Converts the given Perl data structure (a simple scalar or a	99	Converts the given Perl data structure to a UTF-8 encoded, binary
73	reference to a hash or array) to a UTF-8 encoded, binary string
74	(that is, the string contains octets only). Croaks on error.	100	string (that is, the string contains octets only). Croaks on error.
75		101
76	This function call is functionally identical to:	102	This function call is functionally identical to:
77		103
78	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	104	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
79		105
80	except being faster.	106	except being faster.
81		107
82	$perl_scalar = from_json $json_text	108	$perl_scalar = decode_json $json_text
83	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
84	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
85	resulting simple scalar or reference. Croaks on error.	111	resulting reference. Croaks on error.
86		112
87	This function call is functionally identical to:	113	This function call is functionally identical to:
88		114
89	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	115	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
90		116
…		…
97	values in Perl.	123	values in Perl.
98		124
99	See MAPPING, below, for more information on how JSON values are	125	See MAPPING, below, for more information on how JSON values are
100	mapped to Perl.	126	mapped to Perl.
101		127
		128	A FEW NOTES ON UNICODE AND PERL
		129	Since this often leads to confusion, here are a few very clear words on
		130	how Unicode works in Perl, modulo bugs.
		131
		132	1. Perl strings can store characters with ordinal values > 255.
		133	This enables you to store Unicode characters as single characters in
		134	a Perl string - very natural.
		135
		136	2. Perl does not associate an encoding with your strings.
		137	... until you force it to, e.g. when matching it against a regex, or
		138	printing the scalar to a file, in which case Perl either interprets
		139	your string as locale-encoded text, octets/binary, or as Unicode,
		140	depending on various settings. In no case is an encoding stored
		141	together with your data, it is use that decides encoding, not any
		142	magical meta data.
		143
		144	3. The internal utf-8 flag has no meaning with regards to the encoding
		145	of your string.
		146	Just ignore that flag unless you debug a Perl bug, a module written
		147	in XS or want to dive into the internals of perl. Otherwise it will
		148	only confuse you, as, despite the name, it says nothing about how
		149	your string is encoded. You can have Unicode strings with that flag
		150	set, with that flag clear, and you can have binary data with that
		151	flag set and that flag clear. Other possibilities exist, too.
		152
		153	If you didn't know about that flag, just the better, pretend it
		154	doesn't exist.
		155
		156	4. A "Unicode String" is simply a string where each character can be
		157	validly interpreted as a Unicode codepoint.
		158	If you have UTF-8 encoded data, it is no longer a Unicode string,
		159	but a Unicode string encoded in UTF-8, giving you a binary string.
		160
		161	5. A string containing "high" (> 255) character values is not a UTF-8
		162	string.
		163	It's a fact. Learn to live with it.
		164
		165	I hope this helps :)
		166
102	OBJECT-ORIENTED INTERFACE	167	OBJECT-ORIENTED INTERFACE
103	The object oriented interface lets you configure your own encoding or	168	The object oriented interface lets you configure your own encoding or
104	decoding style, within the limits of supported formats.	169	decoding style, within the limits of supported formats.
105		170
106	$json = new JSON::XS	171	$json = new JSON::XS
…		…
113		178
114	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]})
115	=> {"a": [1, 2]}	180	=> {"a": [1, 2]}
116		181
117	$json = $json->ascii ([$enable])	182	$json = $json->ascii ([$enable])
		183	$enabled = $json->get_ascii
118	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
119	generate characters outside the code range 0..127 (which is ASCII).	185	generate characters outside the code range 0..127 (which is ASCII).
120	Any unicode characters outside that range will be escaped using	186	Any Unicode characters outside that range will be escaped using
121	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL	187	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
122	escape sequence, as per RFC4627. The resulting encoded JSON text can	188	escape sequence, as per RFC4627. The resulting encoded JSON text can
123	be treated as a native unicode string, an ascii-encoded,	189	be treated as a native Unicode string, an ascii-encoded,
124	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
125	ASCII.	191	ASCII.
126		192
127	If $enable is false, then the "encode" method will not escape	193	If $enable is false, then the "encode" method will not escape
128	Unicode characters unless required by the JSON syntax or other	194	Unicode characters unless required by the JSON syntax or other
129	flags. This results in a faster and more compact format.	195	flags. This results in a faster and more compact format.
130		196
		197	See also the section ENCODING/CODESET FLAG NOTES later in this
		198	document.
		199
131	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
132	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
133	contain any 8 bit characters.	202	contain any 8 bit characters.
134		203
135	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	204	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
136	=> ["\ud801\udc01"]	205	=> ["\ud801\udc01"]
137		206
138	$json = $json->latin1 ([$enable])	207	$json = $json->latin1 ([$enable])
		208	$enabled = $json->get_latin1
139	If $enable is true (or missing), then the "encode" method will	209	If $enable is true (or missing), then the "encode" method will
140	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
141	any characters outside the code range 0..255. The resulting string	211	any characters outside the code range 0..255. The resulting string
142	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
143	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
144	flag, as "decode" by default expects unicode, which is a strict	214	flag, as "decode" by default expects Unicode, which is a strict
145	superset of latin1.	215	superset of latin1.
146		216
147	If $enable is false, then the "encode" method will not escape	217	If $enable is false, then the "encode" method will not escape
148	Unicode characters unless required by the JSON syntax or other	218	Unicode characters unless required by the JSON syntax or other
149	flags.	219	flags.
		220
		221	See also the section ENCODING/CODESET FLAG NOTES later in this
		222	document.
150		223
151	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
152	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
153	smaller encoded size. The disadvantage is that the resulting JSON	226	smaller encoded size. The disadvantage is that the resulting JSON
154	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
155	when storing and transfering), a rare encoding for JSON. It is	228	when storing and transferring), a rare encoding for JSON. It is
156	therefore most useful when you want to store data structures known	229	therefore most useful when you want to store data structures known
157	to contain binary data efficiently in files or databases, not when	230	to contain binary data efficiently in files or databases, not when
158	talking to other JSON encoders/decoders.	231	talking to other JSON encoders/decoders.
159		232
160	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]	233	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
161	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)	234	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
162		235
163	$json = $json->utf8 ([$enable])	236	$json = $json->utf8 ([$enable])
		237	$enabled = $json->get_utf8
164	If $enable is true (or missing), then the "encode" method will	238	If $enable is true (or missing), then the "encode" method will
165	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,
166	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
167	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
168	characters outside the range 0..255, they are thus useful for	242	characters outside the range 0..255, they are thus useful for
169	bytewise/binary I/O. In future versions, enabling this option might	243	bytewise/binary I/O. In future versions, enabling this option might
170	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
171	described in RFC4627.	245	described in RFC4627.
172		246
173	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
174	string as a (non-encoded) unicode string, while "decode" expects	248	string as a (non-encoded) Unicode string, while "decode" expects
175	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
176	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.
177		254
178	Example, output UTF-16BE-encoded JSON:	255	Example, output UTF-16BE-encoded JSON:
179		256
180	use Encode;	257	use Encode;
181	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	258	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
200	2	277	2
201	]	278	]
202	}	279	}
203		280
204	$json = $json->indent ([$enable])	281	$json = $json->indent ([$enable])
		282	$enabled = $json->get_indent
205	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
206	multiline format as output, putting every array member or	284	multiline format as output, putting every array member or
207	object/hash key-value pair into its own line, identing them	285	object/hash key-value pair into its own line, indenting them
208	properly.	286	properly.
209		287
210	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
211	the resulting JSON text is guarenteed not to contain any "newlines".	289	the resulting JSON text is guaranteed not to contain any "newlines".
212		290
213	This setting has no effect when decoding JSON texts.	291	This setting has no effect when decoding JSON texts.
214		292
215	$json = $json->space_before ([$enable])	293	$json = $json->space_before ([$enable])
		294	$enabled = $json->get_space_before
216	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
217	an extra optional space before the ":" separating keys from values	296	an extra optional space before the ":" separating keys from values
218	in JSON objects.	297	in JSON objects.
219		298
220	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
…		…
226	Example, space_before enabled, space_after and indent disabled:	305	Example, space_before enabled, space_after and indent disabled:
227		306
228	{"key" :"value"}	307	{"key" :"value"}
229		308
230	$json = $json->space_after ([$enable])	309	$json = $json->space_after ([$enable])
		310	$enabled = $json->get_space_after
231	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
232	an extra optional space after the ":" separating keys from values in	312	an extra optional space after the ":" separating keys from values in
233	JSON objects and extra whitespace after the "," separating key-value	313	JSON objects and extra whitespace after the "," separating key-value
234	pairs and array members.	314	pairs and array members.
235		315
…		…
240		320
241	Example, space_before and indent disabled, space_after enabled:	321	Example, space_before and indent disabled, space_after enabled:
242		322
243	{"key": "value"}	323	{"key": "value"}
244		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
245	$json = $json->canonical ([$enable])	367	$json = $json->canonical ([$enable])
		368	$enabled = $json->get_canonical
246	If $enable is true (or missing), then the "encode" method will	369	If $enable is true (or missing), then the "encode" method will
247	output JSON objects by sorting their keys. This is adding a	370	output JSON objects by sorting their keys. This is adding a
248	comparatively high overhead.	371	comparatively high overhead.
249		372
250	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
251	pairs in the order Perl stores them (which will likely change	374	pairs in the order Perl stores them (which will likely change
252	between runs of the same script).	375	between runs of the same script).
253		376
254	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
255	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
256	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
257	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
258	in Perl.	381	in Perl.
259		382
260	This setting has no effect when decoding JSON texts.	383	This setting has no effect when decoding JSON texts.
261		384
262	$json = $json->allow_nonref ([$enable])	385	$json = $json->allow_nonref ([$enable])
		386	$enabled = $json->get_allow_nonref
263	If $enable is true (or missing), then the "encode" method can	387	If $enable is true (or missing), then the "encode" method can
264	convert a non-reference into its corresponding string, number or	388	convert a non-reference into its corresponding string, number or
265	null JSON value, which is an extension to RFC4627. Likewise,	389	null JSON value, which is an extension to RFC4627. Likewise,
266	"decode" will accept those JSON values instead of croaking.	390	"decode" will accept those JSON values instead of croaking.
267		391
…		…
275		399
276	JSON::XS->new->allow_nonref->encode ("Hello, World!")	400	JSON::XS->new->allow_nonref->encode ("Hello, World!")
277	=> "Hello, World!"	401	=> "Hello, World!"
278		402
279	$json = $json->allow_blessed ([$enable])	403	$json = $json->allow_blessed ([$enable])
		404	$enabled = $json->get_allow_blessed
280	If $enable is true (or missing), then the "encode" method will not	405	If $enable is true (or missing), then the "encode" method will not
281	barf when it encounters a blessed reference. Instead, the value of	406	barf when it encounters a blessed reference. Instead, the value of
282	the convert_blessed option will decide wether "null"	407	the convert_blessed option will decide whether "null"
283	("convert_blessed" disabled or no "to_json" method found) or a	408	("convert_blessed" disabled or no "TO_JSON" method found) or a
284	representation of the object ("convert_blessed" enabled and	409	representation of the object ("convert_blessed" enabled and
285	"to_json" method found) is being encoded. Has no effect on "decode".	410	"TO_JSON" method found) is being encoded. Has no effect on "decode".
286		411
287	If $enable is false (the default), then "encode" will throw an	412	If $enable is false (the default), then "encode" will throw an
288	exception when it encounters a blessed object.	413	exception when it encounters a blessed object.
289		414
290	$json = $json->convert_blessed ([$enable])	415	$json = $json->convert_blessed ([$enable])
		416	$enabled = $json->get_convert_blessed
291	If $enable is true (or missing), then "encode", upon encountering a	417	If $enable is true (or missing), then "encode", upon encountering a
292	blessed object, will check for the availability of the "TO_JSON"	418	blessed object, will check for the availability of the "TO_JSON"
293	method on the object's class. If found, it will be called in scalar	419	method on the object's class. If found, it will be called in scalar
294	context and the resulting scalar will be encoded instead of the	420	context and the resulting scalar will be encoded instead of the
295	object. If no "TO_JSON" method is found, the value of	421	object. If no "TO_JSON" method is found, the value of
…		…
299	returns other blessed objects, those will be handled in the same	425	returns other blessed objects, those will be handled in the same
300	way. "TO_JSON" must take care of not causing an endless recursion	426	way. "TO_JSON" must take care of not causing an endless recursion
301	cycle (== crash) in this case. The name of "TO_JSON" was chosen	427	cycle (== crash) in this case. The name of "TO_JSON" was chosen
302	because other methods called by the Perl core (== not by the user of	428	because other methods called by the Perl core (== not by the user of
303	the object) are usually in upper case letters and to avoid	429	the object) are usually in upper case letters and to avoid
304	collisions with the "to_json" function.	430	collisions with any "to_json" function or method.
305		431
306	This setting does not yet influence "decode" in any way, but in the	432	This setting does not yet influence "decode" in any way, but in the
307	future, global hooks might get installed that influence "decode" and	433	future, global hooks might get installed that influence "decode" and
308	are enabled by this setting.	434	are enabled by this setting.
309		435
…		…
350		476
351	As this callback gets called less often then the	477	As this callback gets called less often then the
352	"filter_json_object" one, decoding speed will not usually suffer as	478	"filter_json_object" one, decoding speed will not usually suffer as
353	much. Therefore, single-key objects make excellent targets to	479	much. Therefore, single-key objects make excellent targets to
354	serialise Perl objects into, especially as single-key JSON objects	480	serialise Perl objects into, especially as single-key JSON objects
355	are as close to the type-tagged value concept as JSON gets (its	481	are as close to the type-tagged value concept as JSON gets (it's
356	basically an ID/VALUE tuple). Of course, JSON does not support this	482	basically an ID/VALUE tuple). Of course, JSON does not support this
357	in any way, so you need to make sure your data never looks like a	483	in any way, so you need to make sure your data never looks like a
358	serialised Perl hash.	484	serialised Perl hash.
359		485
360	Typical names for the single object key are "__class_whatever__", or	486	Typical names for the single object key are "__class_whatever__", or
…		…
385		511
386	{ __widget__ => $self->{id} }	512	{ __widget__ => $self->{id} }
387	}	513	}
388		514
389	$json = $json->shrink ([$enable])	515	$json = $json->shrink ([$enable])
		516	$enabled = $json->get_shrink
390	Perl usually over-allocates memory a bit when allocating space for	517	Perl usually over-allocates memory a bit when allocating space for
391	strings. This flag optionally resizes strings generated by either	518	strings. This flag optionally resizes strings generated by either
392	"encode" or "decode" to their minimum size possible. This can save	519	"encode" or "decode" to their minimum size possible. This can save
393	memory when your JSON texts are either very very long or you have	520	memory when your JSON texts are either very very long or you have
394	many short strings. It will also try to downgrade any strings to	521	many short strings. It will also try to downgrade any strings to
…		…
412	converting strings that look like integers or floats into integers	539	converting strings that look like integers or floats into integers
413	or floats internally (there is no difference on the Perl level),	540	or floats internally (there is no difference on the Perl level),
414	saving space.	541	saving space.
415		542
416	$json = $json->max_depth ([$maximum_nesting_depth])	543	$json = $json->max_depth ([$maximum_nesting_depth])
		544	$max_depth = $json->get_max_depth
417	Sets the maximum nesting level (default 512) accepted while encoding	545	Sets the maximum nesting level (default 512) accepted while encoding
418	or decoding. If the JSON text or Perl data structure has an equal or	546	or decoding. If the JSON text or Perl data structure has an equal or
419	higher nesting level then this limit, then the encoder and decoder	547	higher nesting level then this limit, then the encoder and decoder
420	will stop and croak at that point.	548	will stop and croak at that point.
421		549
…		…
433		561
434	See SECURITY CONSIDERATIONS, below, for more info on why this is	562	See SECURITY CONSIDERATIONS, below, for more info on why this is
435	useful.	563	useful.
436		564
437	$json = $json->max_size ([$maximum_string_size])	565	$json = $json->max_size ([$maximum_string_size])
		566	$max_size = $json->get_max_size
438	Set the maximum length a JSON text may have (in bytes) where	567	Set the maximum length a JSON text may have (in bytes) where
439	decoding is being attempted. The default is 0, meaning no limit.	568	decoding is being attempted. The default is 0, meaning no limit.
440	When "decode" is called on a string longer then this number of	569	When "decode" is called on a string longer then this number of
441	characters it will not attempt to decode the string but throw an	570	characters it will not attempt to decode the string but throw an
442	exception. This setting has no effect on "encode" (yet).	571	exception. This setting has no effect on "encode" (yet).
…		…
477	and you need to know where the JSON text ends.	606	and you need to know where the JSON text ends.
478		607
479	JSON::XS->new->decode_prefix ("[1] the tail")	608	JSON::XS->new->decode_prefix ("[1] the tail")
480	=> ([], 3)	609	=> ([], 3)
481		610
		611	INCREMENTAL PARSING
		612	[This section and the API it details is still EXPERIMENTAL]
		613
		614	In some cases, there is the need for incremental parsing of JSON texts.
		615	While this module always has to keep both JSON text and resulting Perl
		616	data structure in memory at one time, it does allow you to parse a JSON
		617	stream incrementally. It does so by accumulating text until it has a
		618	full JSON object, which it then can decode. This process is similar to
		619	using "decode_prefix" to see if a full JSON object is available, but is
		620	much more efficient (JSON::XS will only attempt to parse the JSON text
		621	once it is sure it has enough text to get a decisive result, using a
		622	very simple but truly incremental parser).
		623
		624	The following two methods deal with this.
		625
		626	[void, scalar or list context] = $json->incr_parse ([$string])
		627	This is the central parsing function. It can both append new text
		628	and extract objects from the stream accumulated so far (both of
		629	these functions are optional).
		630
		631	If $string is given, then this string is appended to the already
		632	existing JSON fragment stored in the $json object.
		633
		634	After that, if the function is called in void context, it will
		635	simply return without doing anything further. This can be used to
		636	add more text in as many chunks as you want.
		637
		638	If the method is called in scalar context, then it will try to
		639	extract exactly one JSON object. If that is successful, it will
		640	return this object, otherwise it will return "undef". If there is a
		641	parse error, this method will croak just as "decode" would do (one
		642	can then use "incr_skip" to skip the errornous part). This is the
		643	most common way of using the method.
		644
		645	And finally, in list context, it will try to extract as many objects
		646	from the stream as it can find and return them, or the empty list
		647	otherwise. For this to work, there must be no separators between the
		648	JSON objects or arrays, instead they must be concatenated
		649	back-to-back. If an error occurs, an exception will be raised as in
		650	the scalar context case. Note that in this case, any
		651	previously-parsed JSON texts will be lost.
		652
		653	$lvalue_string = $json->incr_text
		654	This method returns the currently stored JSON fragment as an lvalue,
		655	that is, you can manipulate it. This only works when a preceding
		656	call to "incr_parse" in scalar context successfully returned an
		657	object. Under all other circumstances you must not call this
		658	function (I mean it. although in simple tests it might actually
		659	work, it will fail under real world conditions). As a special
		660	exception, you can also call this method before having parsed
		661	anything.
		662
		663	This function is useful in two cases: a) finding the trailing text
		664	after a JSON object or b) parsing multiple JSON objects separated by
		665	non-JSON text (such as commas).
		666
		667	$json->incr_skip
		668	This will reset the state of the incremental parser and will remove
		669	the parsed text from the input buffer. This is useful after
		670	"incr_parse" died, in which case the input buffer and incremental
		671	parser state is left unchanged, to skip the text parsed so far and
		672	to reset the parse state.
		673
		674	LIMITATIONS
		675	All options that affect decoding are supported, except "allow_nonref".
		676	The reason for this is that it cannot be made to work sensibly: JSON
		677	objects and arrays are self-delimited, i.e. you can concatenate them
		678	back to back and still decode them perfectly. This does not hold true
		679	for JSON numbers, however.
		680
		681	For example, is the string 1 a single JSON number, or is it simply the
		682	start of 12? Or is 12 a single JSON number, or the concatenation of 1
		683	and 2? In neither case you can tell, and this is why JSON::XS takes the
		684	conservative route and disallows this case.
		685
		686	EXAMPLES
		687	Some examples will make all this clearer. First, a simple example that
		688	works similarly to "decode_prefix": We want to decode the JSON object at
		689	the start of a string and identify the portion after the JSON object:
		690
		691	my $text = "[1,2,3] hello";
		692
		693	my $json = new JSON::XS;
		694
		695	my $obj = $json->incr_parse ($text)
		696	or die "expected JSON object or array at beginning of string";
		697
		698	my $tail = $json->incr_text;
		699	# $tail now contains " hello"
		700
		701	Easy, isn't it?
		702
		703	Now for a more complicated example: Imagine a hypothetical protocol
		704	where you read some requests from a TCP stream, and each request is a
		705	JSON array, without any separation between them (in fact, it is often
		706	useful to use newlines as "separators", as these get interpreted as
		707	whitespace at the start of the JSON text, which makes it possible to
		708	test said protocol with "telnet"...).
		709
		710	Here is how you'd do it (it is trivial to write this in an event-based
		711	manner):
		712
		713	my $json = new JSON::XS;
		714
		715	# read some data from the socket
		716	while (sysread $socket, my $buf, 4096) {
		717
		718	# split and decode as many requests as possible
		719	for my $request ($json->incr_parse ($buf)) {
		720	# act on the $request
		721	}
		722	}
		723
		724	Another complicated example: Assume you have a string with JSON objects
		725	or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
		726	[3]"). To parse them, we have to skip the commas between the JSON texts,
		727	and here is where the lvalue-ness of "incr_text" comes in useful:
		728
		729	my $text = "[1],[2], [3]";
		730	my $json = new JSON::XS;
		731
		732	# void context, so no parsing done
		733	$json->incr_parse ($text);
		734
		735	# now extract as many objects as possible. note the
		736	# use of scalar context so incr_text can be called.
		737	while (my $obj = $json->incr_parse) {
		738	# do something with $obj
		739
		740	# now skip the optional comma
		741	$json->incr_text =~ s/^ \s* , //x;
		742	}
		743
		744	Now lets go for a very complex example: Assume that you have a gigantic
		745	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		746	but you cannot load it into memory fully (this has actually happened in
		747	the real world :).
		748
		749	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		750	can still help you: You implement a (very simple) array parser and let
		751	JSON decode the array elements, which are all full JSON objects on their
		752	own (this wouldn't work if the array elements could be JSON numbers, for
		753	example):
		754
		755	my $json = new JSON::XS;
		756
		757	# open the monster
		758	open my $fh, "<bigfile.json"
		759	or die "bigfile: $!";
		760
		761	# first parse the initial "["
		762	for (;;) {
		763	sysread $fh, my $buf, 65536
		764	or die "read error: $!";
		765	$json->incr_parse ($buf); # void context, so no parsing
		766
		767	# Exit the loop once we found and removed(!) the initial "[".
		768	# In essence, we are (ab-)using the $json object as a simple scalar
		769	# we append data to.
		770	last if $json->incr_text =~ s/^ \s* \[ //x;
		771	}
		772
		773	# now we have the skipped the initial "[", so continue
		774	# parsing all the elements.
		775	for (;;) {
		776	# in this loop we read data until we got a single JSON object
		777	for (;;) {
		778	if (my $obj = $json->incr_parse) {
		779	# do something with $obj
		780	last;
		781	}
		782
		783	# add more data
		784	sysread $fh, my $buf, 65536
		785	or die "read error: $!";
		786	$json->incr_parse ($buf); # void context, so no parsing
		787	}
		788
		789	# in this loop we read data until we either found and parsed the
		790	# separating "," between elements, or the final "]"
		791	for (;;) {
		792	# first skip whitespace
		793	$json->incr_text =~ s/^\s*//;
		794
		795	# if we find "]", we are done
		796	if ($json->incr_text =~ s/^\]//) {
		797	print "finished.\n";
		798	exit;
		799	}
		800
		801	# if we find ",", we can continue with the next element
		802	if ($json->incr_text =~ s/^,//) {
		803	last;
		804	}
		805
		806	# if we find anything else, we have a parse error!
		807	if (length $json->incr_text) {
		808	die "parse error near ", $json->incr_text;
		809	}
		810
		811	# else add more data
		812	sysread $fh, my $buf, 65536
		813	or die "read error: $!";
		814	$json->incr_parse ($buf); # void context, so no parsing
		815	}
		816
		817	This is a complex example, but most of the complexity comes from the
		818	fact that we are trying to be correct (bear with me if I am wrong, I
		819	never ran the above example :).
		820
482	MAPPING	821	MAPPING
483	This section describes how JSON::XS maps Perl values to JSON values and	822	This section describes how JSON::XS maps Perl values to JSON values and
484	vice versa. These mappings are designed to "do the right thing" in most	823	vice versa. These mappings are designed to "do the right thing" in most
485	circumstances automatically, preserving round-tripping characteristics	824	circumstances automatically, preserving round-tripping characteristics
486	(what you put in comes out as something equivalent).	825	(what you put in comes out as something equivalent).
487		826
488	For the more enlightened: note that in the following descriptions,	827	For the more enlightened: note that in the following descriptions,
489	lowercase perl refers to the Perl interpreter, while uppcercase Perl	828	lowercase perl refers to the Perl interpreter, while uppercase Perl
490	refers to the abstract Perl language itself.	829	refers to the abstract Perl language itself.
491		830
492	JSON -> PERL	831	JSON -> PERL
493	object	832	object
494	A JSON object becomes a reference to a hash in Perl. No ordering of	833	A JSON object becomes a reference to a hash in Perl. No ordering of
495	object keys is preserved (JSON does not preserver object key	834	object keys is preserved (JSON does not preserve object key ordering
496	ordering itself).	835	itself).
497		836
498	array	837	array
499	A JSON array becomes a reference to an array in Perl.	838	A JSON array becomes a reference to an array in Perl.
500		839
501	string	840	string
502	A JSON string becomes a string scalar in Perl - Unicode codepoints	841	A JSON string becomes a string scalar in Perl - Unicode codepoints
503	in JSON are represented by the same codepoints in the Perl string,	842	in JSON are represented by the same codepoints in the Perl string,
504	so no manual decoding is necessary.	843	so no manual decoding is necessary.
505		844
506	number	845	number
507	A JSON number becomes either an integer or numeric (floating point)	846	A JSON number becomes either an integer, numeric (floating point) or
508	scalar in perl, depending on its range and any fractional parts. On	847	string scalar in perl, depending on its range and any fractional
509	the Perl level, there is no difference between those as Perl handles	848	parts. On the Perl level, there is no difference between those as
510	all the conversion details, but an integer may take slightly less	849	Perl handles all the conversion details, but an integer may take
511	memory and might represent more values exactly than (floating point)	850	slightly less memory and might represent more values exactly than
		851	floating point numbers.
		852
		853	If the number consists of digits only, JSON::XS will try to
		854	represent it as an integer value. If that fails, it will try to
		855	represent it as a numeric (floating point) value if that is possible
		856	without loss of precision. Otherwise it will preserve the number as
		857	a string value (in which case you lose roundtripping ability, as the
		858	JSON number will be re-encoded toa JSON string).
		859
		860	Numbers containing a fractional or exponential part will always be
		861	represented as numeric (floating point) values, possibly at a loss
		862	of precision (in which case you might lose perfect roundtripping
		863	ability, but the JSON number will still be re-encoded as a JSON
512	numbers.	864	number).
513		865
514	true, false	866	true, false
515	These JSON atoms become "JSON::XS::true" and "JSON::XS::false",	867	These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
516	respectively. They are overloaded to act almost exactly like the	868	respectively. They are overloaded to act almost exactly like the
517	numbers 1 and 0. You can check wether a scalar is a JSON boolean by	869	numbers 1 and 0. You can check whether a scalar is a JSON boolean by
518	using the "JSON::XS::is_bool" function.	870	using the "JSON::XS::is_bool" function.
519		871
520	null	872	null
521	A JSON null atom becomes "undef" in Perl.	873	A JSON null atom becomes "undef" in Perl.
522		874
…		…
545	an exception to be thrown, except for references to the integers 0	897	an exception to be thrown, except for references to the integers 0
546	and 1, which get turned into "false" and "true" atoms in JSON. You	898	and 1, which get turned into "false" and "true" atoms in JSON. You
547	can also use "JSON::XS::false" and "JSON::XS::true" to improve	899	can also use "JSON::XS::false" and "JSON::XS::true" to improve
548	readability.	900	readability.
549		901
550	to_json [\0,JSON::XS::true] # yields [false,true]	902	encode_json [\0,JSON::XS::true] # yields [false,true]
551		903
552	JSON::XS::true, JSON::XS::false	904	JSON::XS::true, JSON::XS::false
553	These special values become JSON true and JSON false values,	905	These special values become JSON true and JSON false values,
554	respectively. You cna alos use "\1" and "\0" directly if you want.	906	respectively. You can also use "\1" and "\0" directly if you want.
555		907
556	blessed objects	908	blessed objects
557	Blessed objects are not allowed. JSON::XS currently tries to encode	909	Blessed objects are not directly representable in JSON. See the
558	their underlying representation (hash- or arrayref), but this	910	"allow_blessed" and "convert_blessed" methods on various options on
559	behaviour might change in future versions.	911	how to deal with this: basically, you can choose between throwing an
		912	exception, encoding the reference as if it weren't blessed, or
		913	provide your own serialiser method.
560		914
561	simple scalars	915	simple scalars
562	Simple Perl scalars (any scalar that is not a reference) are the	916	Simple Perl scalars (any scalar that is not a reference) are the
563	most difficult objects to encode: JSON::XS will encode undefined	917	most difficult objects to encode: JSON::XS will encode undefined
564	scalars as JSON null value, scalars that have last been used in a	918	scalars as JSON "null" values, scalars that have last been used in a
565	string context before encoding as JSON strings and anything else as	919	string context before encoding as JSON strings, and anything else as
566	number value:	920	number value:
567		921
568	# dump as number	922	# dump as number
569	to_json [2] # yields [2]	923	encode_json [2] # yields [2]
570	to_json [-3.0e17] # yields [-3e+17]	924	encode_json [-3.0e17] # yields [-3e+17]
571	my $value = 5; to_json [$value] # yields [5]	925	my $value = 5; encode_json [$value] # yields [5]
572		926
573	# used as string, so dump as string	927	# used as string, so dump as string
574	print $value;	928	print $value;
575	to_json [$value] # yields ["5"]	929	encode_json [$value] # yields ["5"]
576		930
577	# undef becomes null	931	# undef becomes null
578	to_json [undef] # yields [null]	932	encode_json [undef] # yields [null]
579		933
580	You can force the type to be a string by stringifying it:	934	You can force the type to be a JSON string by stringifying it:
581		935
582	my $x = 3.1; # some variable containing a number	936	my $x = 3.1; # some variable containing a number
583	"$x"; # stringified	937	"$x"; # stringified
584	$x .= ""; # another, more awkward way to stringify	938	$x .= ""; # another, more awkward way to stringify
585	print $x; # perl does it for you, too, quite often	939	print $x; # perl does it for you, too, quite often
586		940
587	You can force the type to be a number by numifying it:	941	You can force the type to be a JSON number by numifying it:
588		942
589	my $x = "3"; # some variable containing a string	943	my $x = "3"; # some variable containing a string
590	$x += 0; # numify it, ensuring it will be dumped as a number	944	$x += 0; # numify it, ensuring it will be dumped as a number
591	$x *= 1; # same thing, the choise is yours.	945	$x *= 1; # same thing, the choice is yours.
592		946
593	You can not currently output JSON booleans or force the type in	947	You can not currently force the type in other, less obscure, ways.
594	other, less obscure, ways. Tell me if you need this capability.	948	Tell me if you need this capability (but don't forget to explain why
		949	it's needed :).
595		950
596	COMPARISON	951	ENCODING/CODESET FLAG NOTES
597	As already mentioned, this module was created because none of the	952	The interested reader might have seen a number of flags that signify
598	existing JSON modules could be made to work correctly. First I will	953	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
599	describe the problems (or pleasures) I encountered with various existing	954	some confusion on what these do, so here is a short comparison:
600	JSON modules, followed by some benchmark values. JSON::XS was designed
601	not to suffer from any of these problems or limitations.
602		955
603	JSON 1.07	956	"utf8" controls whether the JSON text created by "encode" (and expected
604	Slow (but very portable, as it is written in pure Perl).	957	by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
		958	control whether "encode" escapes character values outside their
		959	respective codeset range. Neither of these flags conflict with each
		960	other, although some combinations make less sense than others.
605		961
606	Undocumented/buggy Unicode handling (how JSON handles unicode values	962	Care has been taken to make all flags symmetrical with respect to
607	is undocumented. One can get far by feeding it unicode strings and	963	"encode" and "decode", that is, texts encoded with any combination of
608	doing en-/decoding oneself, but unicode escapes are not working	964	these flag values will be correctly decoded when the same flags are used
		965	- in general, if you use different flag settings while encoding vs. when
		966	decoding you likely have a bug somewhere.
		967
		968	Below comes a verbose discussion of these flags. Note that a "codeset"
		969	is simply an abstract set of character-codepoint pairs, while an
		970	encoding takes those codepoint numbers and encodes them, in our case
		971	into octets. Unicode is (among other things) a codeset, UTF-8 is an
		972	encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets and
		973	encodings at the same time, which can be confusing.
		974
		975	"utf8" flag disabled
		976	When "utf8" is disabled (the default), then "encode"/"decode"
		977	generate and expect Unicode strings, that is, characters with high
		978	ordinal Unicode values (> 255) will be encoded as such characters,
		979	and likewise such characters are decoded as-is, no canges to them
		980	will be done, except "(re-)interpreting" them as Unicode codepoints
		981	or Unicode characters, respectively (to Perl, these are the same
		982	thing in strings unless you do funny/weird/dumb stuff).
		983
		984	This is useful when you want to do the encoding yourself (e.g. when
		985	you want to have UTF-16 encoded JSON texts) or when some other layer
		986	does the encoding for you (for example, when printing to a terminal
		987	using a filehandle that transparently encodes to UTF-8 you certainly
		988	do NOT want to UTF-8 encode your data first and have Perl encode it
		989	another time).
		990
		991	"utf8" flag enabled
		992	If the "utf8"-flag is enabled, "encode"/"decode" will encode all
		993	characters using the corresponding UTF-8 multi-byte sequence, and
		994	will expect your input strings to be encoded as UTF-8, that is, no
		995	"character" of the input string must have any value > 255, as UTF-8
		996	does not allow that.
		997
		998	The "utf8" flag therefore switches between two modes: disabled means
		999	you will get a Unicode string in Perl, enabled means you get an
		1000	UTF-8 encoded octet/binary string in Perl.
		1001
		1002	"latin1" or "ascii" flags enabled
		1003	With "latin1" (or "ascii") enabled, "encode" will escape characters
		1004	with ordinal values > 255 (> 127 with "ascii") and encode the
		1005	remaining characters as specified by the "utf8" flag.
		1006
		1007	If "utf8" is disabled, then the result is also correctly encoded in
		1008	those character sets (as both are proper subsets of Unicode, meaning
		1009	that a Unicode string with all character values < 256 is the same
		1010	thing as a ISO-8859-1 string, and a Unicode string with all
		1011	character values < 128 is the same thing as an ASCII string in
609	properly).	1012	Perl).
610		1013
611	No roundtripping (strings get clobbered if they look like numbers,	1014	If "utf8" is enabled, you still get a correct UTF-8-encoded string,
612	e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that	1015	regardless of these flags, just some more characters will be escaped
613	will decode into the number 2.	1016	using "\uXXXX" then before.
614		1017
615	JSON::PC 0.01	1018	Note that ISO-8859-1-encoded strings are not compatible with UTF-8
616	Very fast.	1019	encoding, while ASCII-encoded strings are. That is because the
		1020	ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
		1021	codeset being a subset of Unicode), while ASCII is.
617		1022
618	Undocumented/buggy Unicode handling.	1023	Surprisingly, "decode" will ignore these flags and so treat all
		1024	input values as governed by the "utf8" flag. If it is disabled, this
		1025	allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
		1026	strict subsets of Unicode. If it is enabled, you can correctly
		1027	decode UTF-8 encoded strings.
619		1028
620	No roundtripping.	1029	So neither "latin1" nor "ascii" are incompatible with the "utf8"
		1030	flag - they only govern when the JSON output engine escapes a
		1031	character or not.
621		1032
622	Has problems handling many Perl values (e.g. regex results and other	1033	The main use for "latin1" is to relatively efficiently store binary
623	magic values will make it croak).	1034	data as JSON, at the expense of breaking compatibility with most
		1035	JSON decoders.
624		1036
625	Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"	1037	The main use for "ascii" is to force the output to not contain
626	which is not a valid JSON text.	1038	characters with values > 127, which means you can interpret the
627		1039	resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
628	Unmaintained (maintainer unresponsive for many months, bugs are not	1040	any character set and 8-bit-encoding, and still get the same data
629	getting fixed).	1041	structure back. This is useful when your channel for JSON transfer
630		1042	is not 8-bit clean or the encoding might be mangled in between (e.g.
631	JSON::Syck 0.21	1043	in mail), and works because ASCII is a proper subset of most 8-bit
632	Very buggy (often crashes).	1044	and multibyte encodings in use in the world.
633
634	Very inflexible (no human-readable format supported, format pretty
635	much undocumented. I need at least a format for easy reading by
636	humans and a single-line compact format for use in a protocol, and
637	preferably a way to generate ASCII-only JSON texts).
638
639	Completely broken (and confusingly documented) Unicode handling
640	(unicode escapes are not working properly, you need to set
641	ImplicitUnicode to different values on en- and decoding to get
642	symmetric behaviour).
643
644	No roundtripping (simple cases work, but this depends on wether the
645	scalar value was used in a numeric context or not).
646
647	Dumping hashes may skip hash values depending on iterator state.
648
649	Unmaintained (maintainer unresponsive for many months, bugs are not
650	getting fixed).
651
652	Does not check input for validity (i.e. will accept non-JSON input
653	and return "something" instead of raising an exception. This is a
654	security issue: imagine two banks transfering money between each
655	other using JSON. One bank might parse a given non-JSON request and
656	deduct money, while the other might reject the transaction with a
657	syntax error. While a good protocol will at least recover, that is
658	extra unnecessary work and the transaction will still not succeed).
659
660	JSON::DWIW 0.04
661	Very fast. Very natural. Very nice.
662
663	Undocumented unicode handling (but the best of the pack. Unicode
664	escapes still don't get parsed properly).
665
666	Very inflexible.
667
668	No roundtripping.
669
670	Does not generate valid JSON texts (key strings are often unquoted,
671	empty keys result in nothing being output)
672
673	Does not check input for validity.
674		1045
675	JSON and YAML	1046	JSON and YAML
676	You often hear that JSON is a subset (or a close subset) of YAML. This	1047	You often hear that JSON is a subset of YAML. This is, however, a mass
677	is, however, a mass hysteria and very far from the truth. In general,	1048	hysteria(*) and very far from the truth (as of the time of this
678	there is no way to configure JSON::XS to output a data structure as	1049	writing), so let me state it clearly: *in general, there is no way to
679	valid YAML.	1050	configure JSON::XS to output a data structure as valid YAML* that works
		1051	in all cases.
680		1052
681	If you really must use JSON::XS to generate YAML, you should use this	1053	If you really must use JSON::XS to generate YAML, you should use this
682	algorithm (subject to change in future versions):	1054	algorithm (subject to change in future versions):
683		1055
684	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1056	my $to_yaml = JSON::XS->new->utf8->space_after (1);
685	my $yaml = $to_yaml->encode ($ref) . "\n";	1057	my $yaml = $to_yaml->encode ($ref) . "\n";
686		1058
687	This will usually generate JSON texts that also parse as valid YAML.	1059	This will usually generate JSON texts that also parse as valid YAML.
688	Please note that YAML has hardcoded limits on (simple) object key	1060	Please note that YAML has hardcoded limits on (simple) object key
689	lengths that JSON doesn't have, so you should make sure that your hash	1061	lengths that JSON doesn't have and also has different and incompatible
		1062	unicode handling, so you should make sure that your hash keys are
690	keys are noticably shorter than the 1024 characters YAML allows.	1063	noticeably shorter than the 1024 "stream characters" YAML allows and
		1064	that you do not have characters with codepoint values outside the
		1065	Unicode BMP (basic multilingual page). YAML also does not allow "\/"
		1066	sequences in strings (which JSON::XS does not currently generate, but
		1067	other JSON generators might).
691		1068
692	There might be other incompatibilities that I am not aware of. In	1069	There might be other incompatibilities that I am not aware of (or the
		1070	YAML specification has been changed yet again - it does so quite often).
693	general you should not try to generate YAML with a JSON generator or	1071	In general you should not try to generate YAML with a JSON generator or
694	vice versa, or try to parse JSON with a YAML parser or vice versa:	1072	vice versa, or try to parse JSON with a YAML parser or vice versa:
695	chances are high that you will run into severe interoperability	1073	chances are high that you will run into severe interoperability problems
696	problems.	1074	when you least expect it.
		1075
		1076	(*) I have been pressured multiple times by Brian Ingerson (one of the
		1077	authors of the YAML specification) to remove this paragraph, despite
		1078	him acknowledging that the actual incompatibilities exist. As I was
		1079	personally bitten by this "JSON is YAML" lie, I refused and said I
		1080	will continue to educate people about these issues, so others do not
		1081	run into the same problem again and again. After this, Brian called
		1082	me a (quote)complete and worthless idiot(unquote).
		1083
		1084	In my opinion, instead of pressuring and insulting people who
		1085	actually clarify issues with YAML and the wrong statements of some
		1086	of its proponents, I would kindly suggest reading the JSON spec
		1087	(which is not that difficult or long) and finally make YAML
		1088	compatible to it, and educating users about the changes, instead of
		1089	spreading lies about the real compatibility for many years and
		1090	trying to silence people who point out that it isn't true.
697		1091
698	SPEED	1092	SPEED
699	It seems that JSON::XS is surprisingly fast, as shown in the following	1093	It seems that JSON::XS is surprisingly fast, as shown in the following
700	tables. They have been generated with the help of the "eg/bench" program	1094	tables. They have been generated with the help of the "eg/bench" program
701	in the JSON::XS distribution, to make it easy to compare on your own	1095	in the JSON::XS distribution, to make it easy to compare on your own
702	system.	1096	system.
703		1097
704	First comes a comparison between various modules using a very short	1098	First comes a comparison between various modules using a very short
705	single-line JSON string:	1099	single-line JSON string (also available at
		1100	<http://dist.schmorp.de/misc/json/short.json>).
706		1101
707	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1102	{"method": "handleMessage", "params": ["user1", "we were just talking"], \
708	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1103	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
709		1104
710	It shows the number of encodes/decodes per second (JSON::XS uses the	1105	It shows the number of encodes/decodes per second (JSON::XS uses the
711	functional interface, while JSON::XS/2 uses the OO interface with	1106	functional interface, while JSON::XS/2 uses the OO interface with
712	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).	1107	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
713	Higher is better:	1108	Higher is better:
714		1109
715	Storable \| 15779.925 \| 14169.946 \|
716	-----------+------------+------------+
717	module \| encode \| decode \|	1110	module \| encode \| decode \|
718	-----------\|------------\|------------\|	1111	-----------\|------------\|------------\|
719	JSON \| 4990.842 \| 4088.813 \|	1112	JSON 1.x \| 4990.842 \| 4088.813 \|
720	JSON::DWIW \| 51653.990 \| 71575.154 \|	1113	JSON::DWIW \| 51653.990 \| 71575.154 \|
721	JSON::PC \| 65948.176 \| 74631.744 \|	1114	JSON::PC \| 65948.176 \| 74631.744 \|
722	JSON::PP \| 8931.652 \| 3817.168 \|	1115	JSON::PP \| 8931.652 \| 3817.168 \|
723	JSON::Syck \| 24877.248 \| 27776.848 \|	1116	JSON::Syck \| 24877.248 \| 27776.848 \|
724	JSON::XS \| 388361.481 \| 227951.304 \|	1117	JSON::XS \| 388361.481 \| 227951.304 \|
…		…
726	JSON::XS/3 \| 338250.323 \| 218453.333 \|	1119	JSON::XS/3 \| 338250.323 \| 218453.333 \|
727	Storable \| 16500.016 \| 135300.129 \|	1120	Storable \| 16500.016 \| 135300.129 \|
728	-----------+------------+------------+	1121	-----------+------------+------------+
729		1122
730	That is, JSON::XS is about five times faster than JSON::DWIW on	1123	That is, JSON::XS is about five times faster than JSON::DWIW on
731	encoding, about three times faster on decoding, and over fourty times	1124	encoding, about three times faster on decoding, and over forty times
732	faster than JSON, even with pretty-printing and key sorting. It also	1125	faster than JSON, even with pretty-printing and key sorting. It also
733	compares favourably to Storable for small amounts of data.	1126	compares favourably to Storable for small amounts of data.
734		1127
735	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1128	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
736	search API (http://nanoref.com/yahooapis/mgPdGg):	1129	search API (<http://dist.schmorp.de/misc/json/long.json>).
737		1130
738	module \| encode \| decode \|	1131	module \| encode \| decode \|
739	-----------\|------------\|------------\|	1132	-----------\|------------\|------------\|
740	JSON \| 55.260 \| 34.971 \|	1133	JSON 1.x \| 55.260 \| 34.971 \|
741	JSON::DWIW \| 825.228 \| 1082.513 \|	1134	JSON::DWIW \| 825.228 \| 1082.513 \|
742	JSON::PC \| 3571.444 \| 2394.829 \|	1135	JSON::PC \| 3571.444 \| 2394.829 \|
743	JSON::PP \| 210.987 \| 32.574 \|	1136	JSON::PP \| 210.987 \| 32.574 \|
744	JSON::Syck \| 552.551 \| 787.544 \|	1137	JSON::Syck \| 552.551 \| 787.544 \|
745	JSON::XS \| 5780.463 \| 4854.519 \|	1138	JSON::XS \| 5780.463 \| 4854.519 \|
…		…
749	-----------+------------+------------+	1142	-----------+------------+------------+
750		1143
751	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1144	Again, JSON::XS leads by far (except for Storable which non-surprisingly
752	decodes faster).	1145	decodes faster).
753		1146
754	On large strings containing lots of high unicode characters, some	1147	On large strings containing lots of high Unicode characters, some
755	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the	1148	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
756	result will be broken due to missing (or wrong) unicode handling. Others	1149	result will be broken due to missing (or wrong) Unicode handling. Others
757	refuse to decode or encode properly, so it was impossible to prepare a	1150	refuse to decode or encode properly, so it was impossible to prepare a
758	fair comparison table for that case.	1151	fair comparison table for that case.
759		1152
760	SECURITY CONSIDERATIONS	1153	SECURITY CONSIDERATIONS
761	When you are using JSON in a protocol, talking to untrusted potentially	1154	When you are using JSON in a protocol, talking to untrusted potentially
…		…
765	have any buffer overflows. Obviously, this module should ensure that and	1158	have any buffer overflows. Obviously, this module should ensure that and
766	I am trying hard on making that true, but you never know.	1159	I am trying hard on making that true, but you never know.
767		1160
768	Second, you need to avoid resource-starving attacks. That means you	1161	Second, you need to avoid resource-starving attacks. That means you
769	should limit the size of JSON texts you accept, or make sure then when	1162	should limit the size of JSON texts you accept, or make sure then when
770	your resources run out, thats just fine (e.g. by using a separate	1163	your resources run out, that's just fine (e.g. by using a separate
771	process that can crash safely). The size of a JSON text in octets or	1164	process that can crash safely). The size of a JSON text in octets or
772	characters is usually a good indication of the size of the resources	1165	characters is usually a good indication of the size of the resources
773	required to decode it into a Perl structure. While JSON::XS can check	1166	required to decode it into a Perl structure. While JSON::XS can check
774	the size of the JSON text, it might be too late when you already have it	1167	the size of the JSON text, it might be too late when you already have it
775	in memory, so you might want to check the size before you accept the	1168	in memory, so you might want to check the size before you accept the
…		…
778	Third, JSON::XS recurses using the C stack when decoding objects and	1171	Third, JSON::XS recurses using the C stack when decoding objects and
779	arrays. The C stack is a limited resource: for instance, on my amd64	1172	arrays. The C stack is a limited resource: for instance, on my amd64
780	machine with 8MB of stack size I can decode around 180k nested arrays	1173	machine with 8MB of stack size I can decode around 180k nested arrays
781	but only 14k nested JSON objects (due to perl itself recursing deeply on	1174	but only 14k nested JSON objects (due to perl itself recursing deeply on
782	croak to free the temporary). If that is exceeded, the program crashes.	1175	croak to free the temporary). If that is exceeded, the program crashes.
783	to be conservative, the default nesting limit is set to 512. If your	1176	To be conservative, the default nesting limit is set to 512. If your
784	process has a smaller stack, you should adjust this setting accordingly	1177	process has a smaller stack, you should adjust this setting accordingly
785	with the "max_depth" method.	1178	with the "max_depth" method.
786		1179
787	And last but least, something else could bomb you that I forgot to think	1180	Something else could bomb you, too, that I forgot to think of. In that
788	of. In that case, you get to keep the pieces. I am always open for	1181	case, you get to keep the pieces. I am always open for hints, though...
789	hints, though...
790		1182
		1183	Also keep in mind that JSON::XS might leak contents of your Perl data
		1184	structures in its error messages, so when you serialise sensitive
		1185	information you might want to make sure that exceptions thrown by
		1186	JSON::XS will not end up in front of untrusted eyes.
		1187
791	If you are using JSON::XS to return packets to consumption by javascript	1188	If you are using JSON::XS to return packets to consumption by JavaScript
792	scripts in a browser you should have a look at	1189	scripts in a browser you should have a look at
793	<http://jpsykes.com/47/practical-csrf-and-json-security> to see wether	1190	<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
794	you are vulnerable to some common attack vectors (which really are	1191	you are vulnerable to some common attack vectors (which really are
795	browser design bugs, but it is still you who will have to deal with it,	1192	browser design bugs, but it is still you who will have to deal with it,
796	as major browser developers care only for features, not about doing	1193	as major browser developers care only for features, not about getting
797	security right).	1194	security right).
		1195
		1196	THREADS
		1197	This module is not guaranteed to be thread safe and there are no plans
		1198	to change this until Perl gets thread support (as opposed to the
		1199	horribly slow so-called "threads" which are simply slow and bloated
		1200	process simulations - use fork, it's much faster, cheaper, better).
		1201
		1202	(It might actually work, but you have been warned).
798		1203
799	BUGS	1204	BUGS
800	While the goal of this module is to be correct, that unfortunately does	1205	While the goal of this module is to be correct, that unfortunately does
801	not mean its bug-free, only that I think its design is bug-free. It is	1206	not mean it's bug-free, only that I think its design is bug-free. It is
802	still relatively early in its development. If you keep reporting bugs	1207	still relatively early in its development. If you keep reporting bugs
803	they will be fixed swiftly, though.	1208	they will be fixed swiftly, though.
		1209
		1210	Please refrain from using rt.cpan.org or any other bug reporting
		1211	service. I put the contact address into my modules for a reason.
		1212
		1213	SEE ALSO
		1214	The json_xs command line utility for quick experiments.
804		1215
805	AUTHOR	1216	AUTHOR
806	Marc Lehmann <schmorp@schmorp.de>	1217	Marc Lehmann <schmorp@schmorp.de>
807	http://home.schmorp.de/	1218	http://home.schmorp.de/
808		1219

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing JSON-XS/README (file contents): Revision 1.15 by root, Mon Jul 2 08:06:48 2007 UTC vs. Revision 1.24 by root, Thu Mar 27 06:37:35 2008 UTC

Diff Legend

Comparing JSON-XS/README (file contents):
Revision 1.15 by root, Mon Jul 2 08:06:48 2007 UTC vs.
Revision 1.24 by root, Thu Mar 27 06:37:35 2008 UTC