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

Comparing JSON-XS/README (file contents):
Revision 1.20 by root, Tue Nov 13 22:59:08 2007 UTC vs.
Revision 1.41 by root, Wed Nov 16 19:21:53 2016 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	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	シリアライザ/デシリアライザ
6	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)	5	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
7		6
8	SYNOPSIS	7	SYNOPSIS
9	use JSON::XS;	8	use JSON::XS;
10		9
11	# exported functions, they croak on error	10	# exported functions, they croak on error
12	# and expect/generate UTF-8	11	# and expect/generate UTF-8
13		12
14	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	13	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
15	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	14	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
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 and Perl, the deserialised data structure is
47	the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"	62	identical on the Perl level. (e.g. the string "2.0" doesn't suddenly
48	just because it looks like a number).	63	become "2" just because it looks like a number). There are minor
		64	exceptions to this, read the MAPPING section below to learn about
		65	those.
49		66
50	* strict checking of JSON correctness	67	* strict checking of JSON correctness
		68
51	There is no guessing, no generating of illegal JSON texts by	69	There is no guessing, no generating of illegal JSON texts by
52	default, and only JSON is accepted as input by default (the latter	70	default, and only JSON is accepted as input by default (the latter
53	is a security feature).	71	is a security feature).
54		72
55	* fast	73	* fast
56	Compared to other JSON modules, this module compares favourably in
57	terms of speed, too.
58		74
		75	Compared to other JSON modules and other serialisers such as
		76	Storable, this module usually compares favourably in terms of speed,
		77	too.
		78
59	* simple to use	79	* simple to use
		80
60	This module has both a simple functional interface as well as an OO	81	This module has both a simple functional interface as well as an
61	interface.	82	object oriented interface.
62		83
63	* reasonably versatile output formats	84	* reasonably versatile output formats
		85
64	You can choose between the most compact guaranteed single-line	86	You can choose between the most compact guaranteed-single-line
65	format possible (nice for simple line-based protocols), a pure-ascii	87	format possible (nice for simple line-based protocols), a pure-ASCII
66	format (for when your transport is not 8-bit clean, still supports	88	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	89	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	90	want to read that stuff). Or you can combine those features in
69	whatever way you like.	91	whatever way you like.
70		92
71	FUNCTIONAL INTERFACE	93	FUNCTIONAL INTERFACE
72	The following convenience methods are provided by this module. They are	94	The following convenience methods are provided by this module. They are
73	exported by default:	95	exported by default:
74		96
75	$json_text = to_json $perl_scalar	97	$json_text = encode_json $perl_scalar
76	Converts the given Perl data structure to a UTF-8 encoded, binary	98	Converts the given Perl data structure to a UTF-8 encoded, binary
77	string (that is, the string contains octets only). Croaks on error.	99	string (that is, the string contains octets only). Croaks on error.
78		100
79	This function call is functionally identical to:	101	This function call is functionally identical to:
80		102
81	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	103	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
82		104
83	except being faster.	105	Except being faster.
84		106
85	$perl_scalar = from_json $json_text	107	$perl_scalar = decode_json $json_text
86	The opposite of "to_json": expects an UTF-8 (binary) string and	108	The opposite of "encode_json": expects an UTF-8 (binary) string and
87	tries to parse that as an UTF-8 encoded JSON text, returning the	109	tries to parse that as an UTF-8 encoded JSON text, returning the
88	resulting reference. Croaks on error.	110	resulting reference. Croaks on error.
89		111
90	This function call is functionally identical to:	112	This function call is functionally identical to:
91		113
92	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	114	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
93		115
94	except being faster.	116	Except being faster.
95
96	$is_boolean = JSON::XS::is_bool $scalar
97	Returns true if the passed scalar represents either JSON::XS::true
98	or JSON::XS::false, two constants that act like 1 and 0,
99	respectively and are used to represent JSON "true" and "false"
100	values in Perl.
101
102	See MAPPING, below, for more information on how JSON values are
103	mapped to Perl.
104		117
105	A FEW NOTES ON UNICODE AND PERL	118	A FEW NOTES ON UNICODE AND PERL
106	Since this often leads to confusion, here are a few very clear words on	119	Since this often leads to confusion, here are a few very clear words on
107	how Unicode works in Perl, modulo bugs.	120	how Unicode works in Perl, modulo bugs.
108		121
109	1. Perl strings can store characters with ordinal values > 255.	122	1. Perl strings can store characters with ordinal values > 255.
110	This enables you to store Unicode characters as single characters in	123	This enables you to store Unicode characters as single characters in
111	a Perl string - very natural.	124	a Perl string - very natural.
112		125
113	2. Perl does not associate an encoding with your strings.	126	2. Perl does not associate an encoding with your strings.
114	Unless you force it to, e.g. when matching it against a regex, or	127	... until you force it to, e.g. when matching it against a regex, or
115	printing the scalar to a file, in which case Perl either interprets	128	printing the scalar to a file, in which case Perl either interprets
116	your string as locale-encoded text, octets/binary, or as Unicode,	129	your string as locale-encoded text, octets/binary, or as Unicode,
117	depending on various settings. In no case is an encoding stored	130	depending on various settings. In no case is an encoding stored
118	together with your data, it is use that decides encoding, not any	131	together with your data, it is use that decides encoding, not any
119	magical metadata.	132	magical meta data.
120		133
121	3. The internal utf-8 flag has no meaning with regards to the encoding	134	3. The internal utf-8 flag has no meaning with regards to the encoding
122	of your string.	135	of your string.
123	Just ignore that flag unless you debug a Perl bug, a module written	136	Just ignore that flag unless you debug a Perl bug, a module written
124	in XS or want to dive into the internals of perl. Otherwise it will	137	in XS or want to dive into the internals of perl. Otherwise it will
129		142
130	If you didn't know about that flag, just the better, pretend it	143	If you didn't know about that flag, just the better, pretend it
131	doesn't exist.	144	doesn't exist.
132		145
133	4. A "Unicode String" is simply a string where each character can be	146	4. A "Unicode String" is simply a string where each character can be
134	validly interpreted as a Unicode codepoint.	147	validly interpreted as a Unicode code point.
135	If you have UTF-8 encoded data, it is no longer a Unicode string,	148	If you have UTF-8 encoded data, it is no longer a Unicode string,
136	but a Unicode string encoded in UTF-8, giving you a binary string.	149	but a Unicode string encoded in UTF-8, giving you a binary string.
137		150
138	5. A string containing "high" (> 255) character values is not a UTF-8	151	5. A string containing "high" (> 255) character values is not a UTF-8
139	string.	152	string.
…		…
155		168
156	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})	169	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
157	=> {"a": [1, 2]}	170	=> {"a": [1, 2]}
158		171
159	$json = $json->ascii ([$enable])	172	$json = $json->ascii ([$enable])
		173	$enabled = $json->get_ascii
160	If $enable is true (or missing), then the "encode" method will not	174	If $enable is true (or missing), then the "encode" method will not
161	generate characters outside the code range 0..127 (which is ASCII).	175	generate characters outside the code range 0..127 (which is ASCII).
162	Any Unicode characters outside that range will be escaped using	176	Any Unicode characters outside that range will be escaped using
163	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL	177	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
164	escape sequence, as per RFC4627. The resulting encoded JSON text can	178	escape sequence, as per RFC4627. The resulting encoded JSON text can
…		…
168		182
169	If $enable is false, then the "encode" method will not escape	183	If $enable is false, then the "encode" method will not escape
170	Unicode characters unless required by the JSON syntax or other	184	Unicode characters unless required by the JSON syntax or other
171	flags. This results in a faster and more compact format.	185	flags. This results in a faster and more compact format.
172		186
		187	See also the section ENCODING/CODESET FLAG NOTES later in this
		188	document.
		189
173	The main use for this flag is to produce JSON texts that can be	190	The main use for this flag is to produce JSON texts that can be
174	transmitted over a 7-bit channel, as the encoded JSON texts will not	191	transmitted over a 7-bit channel, as the encoded JSON texts will not
175	contain any 8 bit characters.	192	contain any 8 bit characters.
176		193
177	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	194	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
178	=> ["\ud801\udc01"]	195	=> ["\ud801\udc01"]
179		196
180	$json = $json->latin1 ([$enable])	197	$json = $json->latin1 ([$enable])
		198	$enabled = $json->get_latin1
181	If $enable is true (or missing), then the "encode" method will	199	If $enable is true (or missing), then the "encode" method will
182	encode the resulting JSON text as latin1 (or iso-8859-1), escaping	200	encode the resulting JSON text as latin1 (or iso-8859-1), escaping
183	any characters outside the code range 0..255. The resulting string	201	any characters outside the code range 0..255. The resulting string
184	can be treated as a latin1-encoded JSON text or a native Unicode	202	can be treated as a latin1-encoded JSON text or a native Unicode
185	string. The "decode" method will not be affected in any way by this	203	string. The "decode" method will not be affected in any way by this
…		…
187	superset of latin1.	205	superset of latin1.
188		206
189	If $enable is false, then the "encode" method will not escape	207	If $enable is false, then the "encode" method will not escape
190	Unicode characters unless required by the JSON syntax or other	208	Unicode characters unless required by the JSON syntax or other
191	flags.	209	flags.
		210
		211	See also the section ENCODING/CODESET FLAG NOTES later in this
		212	document.
192		213
193	The main use for this flag is efficiently encoding binary data as	214	The main use for this flag is efficiently encoding binary data as
194	JSON text, as most octets will not be escaped, resulting in a	215	JSON text, as most octets will not be escaped, resulting in a
195	smaller encoded size. The disadvantage is that the resulting JSON	216	smaller encoded size. The disadvantage is that the resulting JSON
196	text is encoded in latin1 (and must correctly be treated as such	217	text is encoded in latin1 (and must correctly be treated as such
…		…
201		222
202	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]	223	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
203	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)	224	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
204		225
205	$json = $json->utf8 ([$enable])	226	$json = $json->utf8 ([$enable])
		227	$enabled = $json->get_utf8
206	If $enable is true (or missing), then the "encode" method will	228	If $enable is true (or missing), then the "encode" method will
207	encode the JSON result into UTF-8, as required by many protocols,	229	encode the JSON result into UTF-8, as required by many protocols,
208	while the "decode" method expects to be handled an UTF-8-encoded	230	while the "decode" method expects to be handled an UTF-8-encoded
209	string. Please note that UTF-8-encoded strings do not contain any	231	string. Please note that UTF-8-encoded strings do not contain any
210	characters outside the range 0..255, they are thus useful for	232	characters outside the range 0..255, they are thus useful for
…		…
215	If $enable is false, then the "encode" method will return the JSON	237	If $enable is false, then the "encode" method will return the JSON
216	string as a (non-encoded) Unicode string, while "decode" expects	238	string as a (non-encoded) Unicode string, while "decode" expects
217	thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or	239	thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or
218	UTF-16) needs to be done yourself, e.g. using the Encode module.	240	UTF-16) needs to be done yourself, e.g. using the Encode module.
219		241
		242	See also the section ENCODING/CODESET FLAG NOTES later in this
		243	document.
		244
220	Example, output UTF-16BE-encoded JSON:	245	Example, output UTF-16BE-encoded JSON:
221		246
222	use Encode;	247	use Encode;
223	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	248	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
224		249
…		…
242	2	267	2
243	]	268	]
244	}	269	}
245		270
246	$json = $json->indent ([$enable])	271	$json = $json->indent ([$enable])
		272	$enabled = $json->get_indent
247	If $enable is true (or missing), then the "encode" method will use a	273	If $enable is true (or missing), then the "encode" method will use a
248	multiline format as output, putting every array member or	274	multiline format as output, putting every array member or
249	object/hash key-value pair into its own line, indenting them	275	object/hash key-value pair into its own line, indenting them
250	properly.	276	properly.
251		277
…		…
253	the resulting JSON text is guaranteed not to contain any "newlines".	279	the resulting JSON text is guaranteed not to contain any "newlines".
254		280
255	This setting has no effect when decoding JSON texts.	281	This setting has no effect when decoding JSON texts.
256		282
257	$json = $json->space_before ([$enable])	283	$json = $json->space_before ([$enable])
		284	$enabled = $json->get_space_before
258	If $enable is true (or missing), then the "encode" method will add	285	If $enable is true (or missing), then the "encode" method will add
259	an extra optional space before the ":" separating keys from values	286	an extra optional space before the ":" separating keys from values
260	in JSON objects.	287	in JSON objects.
261		288
262	If $enable is false, then the "encode" method will not add any extra	289	If $enable is false, then the "encode" method will not add any extra
…		…
268	Example, space_before enabled, space_after and indent disabled:	295	Example, space_before enabled, space_after and indent disabled:
269		296
270	{"key" :"value"}	297	{"key" :"value"}
271		298
272	$json = $json->space_after ([$enable])	299	$json = $json->space_after ([$enable])
		300	$enabled = $json->get_space_after
273	If $enable is true (or missing), then the "encode" method will add	301	If $enable is true (or missing), then the "encode" method will add
274	an extra optional space after the ":" separating keys from values in	302	an extra optional space after the ":" separating keys from values in
275	JSON objects and extra whitespace after the "," separating key-value	303	JSON objects and extra whitespace after the "," separating key-value
276	pairs and array members.	304	pairs and array members.
277		305
…		…
283	Example, space_before and indent disabled, space_after enabled:	311	Example, space_before and indent disabled, space_after enabled:
284		312
285	{"key": "value"}	313	{"key": "value"}
286		314
287	$json = $json->relaxed ([$enable])	315	$json = $json->relaxed ([$enable])
		316	$enabled = $json->get_relaxed
288	If $enable is true (or missing), then "decode" will accept some	317	If $enable is true (or missing), then "decode" will accept some
289	extensions to normal JSON syntax (see below). "encode" will not be	318	extensions to normal JSON syntax (see below). "encode" will not be
290	affected in anyway. *Be aware that this option makes you accept	319	affected in anyway. *Be aware that this option makes you accept
291	invalid JSON texts as if they were valid!*. I suggest only to use	320	invalid JSON texts as if they were valid!*. I suggest only to use
292	this option to parse application-specific files written by humans	321	this option to parse application-specific files written by humans
…		…
295	If $enable is false (the default), then "decode" will only accept	324	If $enable is false (the default), then "decode" will only accept
296	valid JSON texts.	325	valid JSON texts.
297		326
298	Currently accepted extensions are:	327	Currently accepted extensions are:
299		328
300	* list items can have an end-comma	329	* list items can have an end-comma
		330
301	JSON separates array elements and key-value pairs with commas.	331	JSON separates array elements and key-value pairs with commas.
302	This can be annoying if you write JSON texts manually and want	332	This can be annoying if you write JSON texts manually and want
303	to be able to quickly append elements, so this extension accepts	333	to be able to quickly append elements, so this extension accepts
304	comma at the end of such items not just between them:	334	comma at the end of such items not just between them:
305		335
…		…
310	{	340	{
311	"k1": "v1",	341	"k1": "v1",
312	"k2": "v2", <- this comma not normally allowed	342	"k2": "v2", <- this comma not normally allowed
313	}	343	}
314		344
315	* shell-style '#'-comments	345	* shell-style '#'-comments
		346
316	Whenever JSON allows whitespace, shell-style comments are	347	Whenever JSON allows whitespace, shell-style comments are
317	additionally allowed. They are terminated by the first	348	additionally allowed. They are terminated by the first
318	carriage-return or line-feed character, after which more	349	carriage-return or line-feed character, after which more
319	white-space and comments are allowed.	350	white-space and comments are allowed.
320		351
321	[	352	[
322	1, # this comment not allowed in JSON	353	1, # this comment not allowed in JSON
323	# neither this one...	354	# neither this one...
324	]	355	]
325		356
		357	* literal ASCII TAB characters in strings
		358
		359	Literal ASCII TAB characters are now allowed in strings (and
		360	treated as "\t").
		361
		362	[
		363	"Hello\tWorld",
		364	"Hello<TAB>World", # literal <TAB> would not normally be allowed
		365	]
		366
326	$json = $json->canonical ([$enable])	367	$json = $json->canonical ([$enable])
		368	$enabled = $json->get_canonical
327	If $enable is true (or missing), then the "encode" method will	369	If $enable is true (or missing), then the "encode" method will
328	output JSON objects by sorting their keys. This is adding a	370	output JSON objects by sorting their keys. This is adding a
329	comparatively high overhead.	371	comparatively high overhead.
330		372
331	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
332	pairs in the order Perl stores them (which will likely change	374	pairs in the order Perl stores them (which will likely change
333	between runs of the same script).	375	between runs of the same script, and can change even within the same
		376	run from 5.18 onwards).
334		377
335	This option is useful if you want the same data structure to be	378	This option is useful if you want the same data structure to be
336	encoded as the same JSON text (given the same overall settings). If	379	encoded as the same JSON text (given the same overall settings). If
337	it is disabled, the same hash might be encoded differently even if	380	it is disabled, the same hash might be encoded differently even if
338	contains the same data, as key-value pairs have no inherent ordering	381	contains the same data, as key-value pairs have no inherent ordering
339	in Perl.	382	in Perl.
340		383
341	This setting has no effect when decoding JSON texts.	384	This setting has no effect when decoding JSON texts.
342		385
		386	This setting has currently no effect on tied hashes.
		387
343	$json = $json->allow_nonref ([$enable])	388	$json = $json->allow_nonref ([$enable])
		389	$enabled = $json->get_allow_nonref
344	If $enable is true (or missing), then the "encode" method can	390	If $enable is true (or missing), then the "encode" method can
345	convert a non-reference into its corresponding string, number or	391	convert a non-reference into its corresponding string, number or
346	null JSON value, which is an extension to RFC4627. Likewise,	392	null JSON value, which is an extension to RFC4627. Likewise,
347	"decode" will accept those JSON values instead of croaking.	393	"decode" will accept those JSON values instead of croaking.
348		394
…		…
355	"allow_nonref", resulting in an invalid JSON text:	401	"allow_nonref", resulting in an invalid JSON text:
356		402
357	JSON::XS->new->allow_nonref->encode ("Hello, World!")	403	JSON::XS->new->allow_nonref->encode ("Hello, World!")
358	=> "Hello, World!"	404	=> "Hello, World!"
359		405
		406	$json = $json->allow_unknown ([$enable])
		407	$enabled = $json->get_allow_unknown
		408	If $enable is true (or missing), then "encode" will not throw an
		409	exception when it encounters values it cannot represent in JSON (for
		410	example, filehandles) but instead will encode a JSON "null" value.
		411	Note that blessed objects are not included here and are handled
		412	separately by c<allow_nonref>.
		413
		414	If $enable is false (the default), then "encode" will throw an
		415	exception when it encounters anything it cannot encode as JSON.
		416
		417	This option does not affect "decode" in any way, and it is
		418	recommended to leave it off unless you know your communications
		419	partner.
		420
360	$json = $json->allow_blessed ([$enable])	421	$json = $json->allow_blessed ([$enable])
		422	$enabled = $json->get_allow_blessed
		423	See "OBJECT SERIALISATION" for details.
		424
361	If $enable is true (or missing), then the "encode" method will not	425	If $enable is true (or missing), then the "encode" method will not
362	barf when it encounters a blessed reference. Instead, the value of	426	barf when it encounters a blessed reference that it cannot convert
363	the convert_blessed option will decide whether "null"	427	otherwise. Instead, a JSON "null" value is encoded instead of the
364	("convert_blessed" disabled or no "to_json" method found) or a	428	object.
365	representation of the object ("convert_blessed" enabled and
366	"to_json" method found) is being encoded. Has no effect on "decode".
367		429
368	If $enable is false (the default), then "encode" will throw an	430	If $enable is false (the default), then "encode" will throw an
369	exception when it encounters a blessed object.	431	exception when it encounters a blessed object that it cannot convert
		432	otherwise.
		433
		434	This setting has no effect on "decode".
370		435
371	$json = $json->convert_blessed ([$enable])	436	$json = $json->convert_blessed ([$enable])
		437	$enabled = $json->get_convert_blessed
		438	See "OBJECT SERIALISATION" for details.
		439
372	If $enable is true (or missing), then "encode", upon encountering a	440	If $enable is true (or missing), then "encode", upon encountering a
373	blessed object, will check for the availability of the "TO_JSON"	441	blessed object, will check for the availability of the "TO_JSON"
374	method on the object's class. If found, it will be called in scalar	442	method on the object's class. If found, it will be called in scalar
375	context and the resulting scalar will be encoded instead of the	443	context and the resulting scalar will be encoded instead of the
376	object. If no "TO_JSON" method is found, the value of	444	object.
377	"allow_blessed" will decide what to do.
378		445
379	The "TO_JSON" method may safely call die if it wants. If "TO_JSON"	446	The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
380	returns other blessed objects, those will be handled in the same	447	returns other blessed objects, those will be handled in the same
381	way. "TO_JSON" must take care of not causing an endless recursion	448	way. "TO_JSON" must take care of not causing an endless recursion
382	cycle (== crash) in this case. The name of "TO_JSON" was chosen	449	cycle (== crash) in this case. The name of "TO_JSON" was chosen
383	because other methods called by the Perl core (== not by the user of	450	because other methods called by the Perl core (== not by the user of
384	the object) are usually in upper case letters and to avoid	451	the object) are usually in upper case letters and to avoid
385	collisions with the "to_json" function.	452	collisions with any "to_json" function or method.
386		453
387	This setting does not yet influence "decode" in any way, but in the	454	If $enable is false (the default), then "encode" will not consider
388	future, global hooks might get installed that influence "decode" and	455	this type of conversion.
389	are enabled by this setting.
390		456
391	If $enable is false, then the "allow_blessed" setting will decide	457	This setting has no effect on "decode".
392	what to do when a blessed object is found.	458
		459	$json = $json->allow_tags ([$enable])
		460	$enabled = $json->allow_tags
		461	See "OBJECT SERIALISATION" for details.
		462
		463	If $enable is true (or missing), then "encode", upon encountering a
		464	blessed object, will check for the availability of the "FREEZE"
		465	method on the object's class. If found, it will be used to serialise
		466	the object into a nonstandard tagged JSON value (that JSON decoders
		467	cannot decode).
		468
		469	It also causes "decode" to parse such tagged JSON values and
		470	deserialise them via a call to the "THAW" method.
		471
		472	If $enable is false (the default), then "encode" will not consider
		473	this type of conversion, and tagged JSON values will cause a parse
		474	error in "decode", as if tags were not part of the grammar.
393		475
394	$json = $json->filter_json_object ([$coderef->($hashref)])	476	$json = $json->filter_json_object ([$coderef->($hashref)])
395	When $coderef is specified, it will be called from "decode" each	477	When $coderef is specified, it will be called from "decode" each
396	time it decodes a JSON object. The only argument is a reference to	478	time it decodes a JSON object. The only argument is a reference to
397	the newly-created hash. If the code references returns a single	479	the newly-created hash. If the code references returns a single
…		…
466		548
467	{ __widget__ => $self->{id} }	549	{ __widget__ => $self->{id} }
468	}	550	}
469		551
470	$json = $json->shrink ([$enable])	552	$json = $json->shrink ([$enable])
		553	$enabled = $json->get_shrink
471	Perl usually over-allocates memory a bit when allocating space for	554	Perl usually over-allocates memory a bit when allocating space for
472	strings. This flag optionally resizes strings generated by either	555	strings. This flag optionally resizes strings generated by either
473	"encode" or "decode" to their minimum size possible. This can save	556	"encode" or "decode" to their minimum size possible. This can save
474	memory when your JSON texts are either very very long or you have	557	memory when your JSON texts are either very very long or you have
475	many short strings. It will also try to downgrade any strings to	558	many short strings. It will also try to downgrade any strings to
…		…
493	converting strings that look like integers or floats into integers	576	converting strings that look like integers or floats into integers
494	or floats internally (there is no difference on the Perl level),	577	or floats internally (there is no difference on the Perl level),
495	saving space.	578	saving space.
496		579
497	$json = $json->max_depth ([$maximum_nesting_depth])	580	$json = $json->max_depth ([$maximum_nesting_depth])
		581	$max_depth = $json->get_max_depth
498	Sets the maximum nesting level (default 512) accepted while encoding	582	Sets the maximum nesting level (default 512) accepted while encoding
499	or decoding. If the JSON text or Perl data structure has an equal or	583	or decoding. If a higher nesting level is detected in JSON text or a
500	higher nesting level then this limit, then the encoder and decoder	584	Perl data structure, then the encoder and decoder will stop and
501	will stop and croak at that point.	585	croak at that point.
502		586
503	Nesting level is defined by number of hash- or arrayrefs that the	587	Nesting level is defined by number of hash- or arrayrefs that the
504	encoder needs to traverse to reach a given point or the number of	588	encoder needs to traverse to reach a given point or the number of
505	"{" or "[" characters without their matching closing parenthesis	589	"{" or "[" characters without their matching closing parenthesis
506	crossed to reach a given character in a string.	590	crossed to reach a given character in a string.
507		591
508	Setting the maximum depth to one disallows any nesting, so that	592	Setting the maximum depth to one disallows any nesting, so that
509	ensures that the object is only a single hash/object or array.	593	ensures that the object is only a single hash/object or array.
510		594
511	The argument to "max_depth" will be rounded up to the next highest
512	power of two. If no argument is given, the highest possible setting	595	If no argument is given, the highest possible setting will be used,
513	will be used, which is rarely useful.	596	which is rarely useful.
		597
		598	Note that nesting is implemented by recursion in C. The default
		599	value has been chosen to be as large as typical operating systems
		600	allow without crashing.
514		601
515	See SECURITY CONSIDERATIONS, below, for more info on why this is	602	See SECURITY CONSIDERATIONS, below, for more info on why this is
516	useful.	603	useful.
517		604
518	$json = $json->max_size ([$maximum_string_size])	605	$json = $json->max_size ([$maximum_string_size])
		606	$max_size = $json->get_max_size
519	Set the maximum length a JSON text may have (in bytes) where	607	Set the maximum length a JSON text may have (in bytes) where
520	decoding is being attempted. The default is 0, meaning no limit.	608	decoding is being attempted. The default is 0, meaning no limit.
521	When "decode" is called on a string longer then this number of	609	When "decode" is called on a string that is longer then this many
522	characters it will not attempt to decode the string but throw an	610	bytes, it will not attempt to decode the string but throw an
523	exception. This setting has no effect on "encode" (yet).	611	exception. This setting has no effect on "encode" (yet).
524		612
525	The argument to "max_size" will be rounded up to the next highest
526	power of two (so may be more than requested). If no argument is
527	given, the limit check will be deactivated (same as when 0 is	613	If no argument is given, the limit check will be deactivated (same
528	specified).	614	as when 0 is specified).
529		615
530	See SECURITY CONSIDERATIONS, below, for more info on why this is	616	See SECURITY CONSIDERATIONS, below, for more info on why this is
531	useful.	617	useful.
532		618
533	$json_text = $json->encode ($perl_scalar)	619	$json_text = $json->encode ($perl_scalar)
534	Converts the given Perl data structure (a simple scalar or a	620	Converts the given Perl value or data structure to its JSON
535	reference to a hash or array) to its JSON representation. Simple	621	representation. Croaks on error.
536	scalars will be converted into JSON string or number sequences,
537	while references to arrays become JSON arrays and references to
538	hashes become JSON objects. Undefined Perl values (e.g. "undef")
539	become JSON "null" values. Neither "true" nor "false" values will be
540	generated.
541		622
542	$perl_scalar = $json->decode ($json_text)	623	$perl_scalar = $json->decode ($json_text)
543	The opposite of "encode": expects a JSON text and tries to parse it,	624	The opposite of "encode": expects a JSON text and tries to parse it,
544	returning the resulting simple scalar or reference. Croaks on error.	625	returning the resulting simple scalar or reference. Croaks on error.
545
546	JSON numbers and strings become simple Perl scalars. JSON arrays
547	become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
548	becomes 1, "false" becomes 0 and "null" becomes "undef".
549		626
550	($perl_scalar, $characters) = $json->decode_prefix ($json_text)	627	($perl_scalar, $characters) = $json->decode_prefix ($json_text)
551	This works like the "decode" method, but instead of raising an	628	This works like the "decode" method, but instead of raising an
552	exception when there is trailing garbage after the first JSON	629	exception when there is trailing garbage after the first JSON
553	object, it will silently stop parsing there and return the number of	630	object, it will silently stop parsing there and return the number of
554	characters consumed so far.	631	characters consumed so far.
555		632
556	This is useful if your JSON texts are not delimited by an outer	633	This is useful if your JSON texts are not delimited by an outer
557	protocol (which is not the brightest thing to do in the first place)
558	and you need to know where the JSON text ends.	634	protocol and you need to know where the JSON text ends.
559		635
560	JSON::XS->new->decode_prefix ("[1] the tail")	636	JSON::XS->new->decode_prefix ("[1] the tail")
561	=> ([], 3)	637	=> ([1], 3)
		638
		639	INCREMENTAL PARSING
		640	In some cases, there is the need for incremental parsing of JSON texts.
		641	While this module always has to keep both JSON text and resulting Perl
		642	data structure in memory at one time, it does allow you to parse a JSON
		643	stream incrementally. It does so by accumulating text until it has a
		644	full JSON object, which it then can decode. This process is similar to
		645	using "decode_prefix" to see if a full JSON object is available, but is
		646	much more efficient (and can be implemented with a minimum of method
		647	calls).
		648
		649	JSON::XS will only attempt to parse the JSON text once it is sure it has
		650	enough text to get a decisive result, using a very simple but truly
		651	incremental parser. This means that it sometimes won't stop as early as
		652	the full parser, for example, it doesn't detect mismatched parentheses.
		653	The only thing it guarantees is that it starts decoding as soon as a
		654	syntactically valid JSON text has been seen. This means you need to set
		655	resource limits (e.g. "max_size") to ensure the parser will stop parsing
		656	in the presence if syntax errors.
		657
		658	The following methods implement this incremental parser.
		659
		660	[void, scalar or list context] = $json->incr_parse ([$string])
		661	This is the central parsing function. It can both append new text
		662	and extract objects from the stream accumulated so far (both of
		663	these functions are optional).
		664
		665	If $string is given, then this string is appended to the already
		666	existing JSON fragment stored in the $json object.
		667
		668	After that, if the function is called in void context, it will
		669	simply return without doing anything further. This can be used to
		670	add more text in as many chunks as you want.
		671
		672	If the method is called in scalar context, then it will try to
		673	extract exactly one JSON object. If that is successful, it will
		674	return this object, otherwise it will return "undef". If there is a
		675	parse error, this method will croak just as "decode" would do (one
		676	can then use "incr_skip" to skip the erroneous part). This is the
		677	most common way of using the method.
		678
		679	And finally, in list context, it will try to extract as many objects
		680	from the stream as it can find and return them, or the empty list
		681	otherwise. For this to work, there must be no separators (other than
		682	whitespace) between the JSON objects or arrays, instead they must be
		683	concatenated back-to-back. If an error occurs, an exception will be
		684	raised as in the scalar context case. Note that in this case, any
		685	previously-parsed JSON texts will be lost.
		686
		687	Example: Parse some JSON arrays/objects in a given string and return
		688	them.
		689
		690	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		691
		692	$lvalue_string = $json->incr_text
		693	This method returns the currently stored JSON fragment as an lvalue,
		694	that is, you can manipulate it. This only works when a preceding
		695	call to "incr_parse" in scalar context successfully returned an
		696	object. Under all other circumstances you must not call this
		697	function (I mean it. although in simple tests it might actually
		698	work, it will fail under real world conditions). As a special
		699	exception, you can also call this method before having parsed
		700	anything.
		701
		702	That means you can only use this function to look at or manipulate
		703	text before or after complete JSON objects, not while the parser is
		704	in the middle of parsing a JSON object.
		705
		706	This function is useful in two cases: a) finding the trailing text
		707	after a JSON object or b) parsing multiple JSON objects separated by
		708	non-JSON text (such as commas).
		709
		710	$json->incr_skip
		711	This will reset the state of the incremental parser and will remove
		712	the parsed text from the input buffer so far. This is useful after
		713	"incr_parse" died, in which case the input buffer and incremental
		714	parser state is left unchanged, to skip the text parsed so far and
		715	to reset the parse state.
		716
		717	The difference to "incr_reset" is that only text until the parse
		718	error occurred is removed.
		719
		720	$json->incr_reset
		721	This completely resets the incremental parser, that is, after this
		722	call, it will be as if the parser had never parsed anything.
		723
		724	This is useful if you want to repeatedly parse JSON objects and want
		725	to ignore any trailing data, which means you have to reset the
		726	parser after each successful decode.
		727
		728	LIMITATIONS
		729	All options that affect decoding are supported, except "allow_nonref".
		730	The reason for this is that it cannot be made to work sensibly: JSON
		731	objects and arrays are self-delimited, i.e. you can concatenate them
		732	back to back and still decode them perfectly. This does not hold true
		733	for JSON numbers, however.
		734
		735	For example, is the string 1 a single JSON number, or is it simply the
		736	start of 12? Or is 12 a single JSON number, or the concatenation of 1
		737	and 2? In neither case you can tell, and this is why JSON::XS takes the
		738	conservative route and disallows this case.
		739
		740	EXAMPLES
		741	Some examples will make all this clearer. First, a simple example that
		742	works similarly to "decode_prefix": We want to decode the JSON object at
		743	the start of a string and identify the portion after the JSON object:
		744
		745	my $text = "[1,2,3] hello";
		746
		747	my $json = new JSON::XS;
		748
		749	my $obj = $json->incr_parse ($text)
		750	or die "expected JSON object or array at beginning of string";
		751
		752	my $tail = $json->incr_text;
		753	# $tail now contains " hello"
		754
		755	Easy, isn't it?
		756
		757	Now for a more complicated example: Imagine a hypothetical protocol
		758	where you read some requests from a TCP stream, and each request is a
		759	JSON array, without any separation between them (in fact, it is often
		760	useful to use newlines as "separators", as these get interpreted as
		761	whitespace at the start of the JSON text, which makes it possible to
		762	test said protocol with "telnet"...).
		763
		764	Here is how you'd do it (it is trivial to write this in an event-based
		765	manner):
		766
		767	my $json = new JSON::XS;
		768
		769	# read some data from the socket
		770	while (sysread $socket, my $buf, 4096) {
		771
		772	# split and decode as many requests as possible
		773	for my $request ($json->incr_parse ($buf)) {
		774	# act on the $request
		775	}
		776	}
		777
		778	Another complicated example: Assume you have a string with JSON objects
		779	or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
		780	[3]"). To parse them, we have to skip the commas between the JSON texts,
		781	and here is where the lvalue-ness of "incr_text" comes in useful:
		782
		783	my $text = "[1],[2], [3]";
		784	my $json = new JSON::XS;
		785
		786	# void context, so no parsing done
		787	$json->incr_parse ($text);
		788
		789	# now extract as many objects as possible. note the
		790	# use of scalar context so incr_text can be called.
		791	while (my $obj = $json->incr_parse) {
		792	# do something with $obj
		793
		794	# now skip the optional comma
		795	$json->incr_text =~ s/^ \s* , //x;
		796	}
		797
		798	Now lets go for a very complex example: Assume that you have a gigantic
		799	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		800	but you cannot load it into memory fully (this has actually happened in
		801	the real world :).
		802
		803	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		804	can still help you: You implement a (very simple) array parser and let
		805	JSON decode the array elements, which are all full JSON objects on their
		806	own (this wouldn't work if the array elements could be JSON numbers, for
		807	example):
		808
		809	my $json = new JSON::XS;
		810
		811	# open the monster
		812	open my $fh, "<bigfile.json"
		813	or die "bigfile: $!";
		814
		815	# first parse the initial "["
		816	for (;;) {
		817	sysread $fh, my $buf, 65536
		818	or die "read error: $!";
		819	$json->incr_parse ($buf); # void context, so no parsing
		820
		821	# Exit the loop once we found and removed(!) the initial "[".
		822	# In essence, we are (ab-)using the $json object as a simple scalar
		823	# we append data to.
		824	last if $json->incr_text =~ s/^ \s* \[ //x;
		825	}
		826
		827	# now we have the skipped the initial "[", so continue
		828	# parsing all the elements.
		829	for (;;) {
		830	# in this loop we read data until we got a single JSON object
		831	for (;;) {
		832	if (my $obj = $json->incr_parse) {
		833	# do something with $obj
		834	last;
		835	}
		836
		837	# add more data
		838	sysread $fh, my $buf, 65536
		839	or die "read error: $!";
		840	$json->incr_parse ($buf); # void context, so no parsing
		841	}
		842
		843	# in this loop we read data until we either found and parsed the
		844	# separating "," between elements, or the final "]"
		845	for (;;) {
		846	# first skip whitespace
		847	$json->incr_text =~ s/^\s*//;
		848
		849	# if we find "]", we are done
		850	if ($json->incr_text =~ s/^\]//) {
		851	print "finished.\n";
		852	exit;
		853	}
		854
		855	# if we find ",", we can continue with the next element
		856	if ($json->incr_text =~ s/^,//) {
		857	last;
		858	}
		859
		860	# if we find anything else, we have a parse error!
		861	if (length $json->incr_text) {
		862	die "parse error near ", $json->incr_text;
		863	}
		864
		865	# else add more data
		866	sysread $fh, my $buf, 65536
		867	or die "read error: $!";
		868	$json->incr_parse ($buf); # void context, so no parsing
		869	}
		870
		871	This is a complex example, but most of the complexity comes from the
		872	fact that we are trying to be correct (bear with me if I am wrong, I
		873	never ran the above example :).
562		874
563	MAPPING	875	MAPPING
564	This section describes how JSON::XS maps Perl values to JSON values and	876	This section describes how JSON::XS maps Perl values to JSON values and
565	vice versa. These mappings are designed to "do the right thing" in most	877	vice versa. These mappings are designed to "do the right thing" in most
566	circumstances automatically, preserving round-tripping characteristics	878	circumstances automatically, preserving round-tripping characteristics
…		…
588	A JSON number becomes either an integer, numeric (floating point) or	900	A JSON number becomes either an integer, numeric (floating point) or
589	string scalar in perl, depending on its range and any fractional	901	string scalar in perl, depending on its range and any fractional
590	parts. On the Perl level, there is no difference between those as	902	parts. On the Perl level, there is no difference between those as
591	Perl handles all the conversion details, but an integer may take	903	Perl handles all the conversion details, but an integer may take
592	slightly less memory and might represent more values exactly than	904	slightly less memory and might represent more values exactly than
593	(floating point) numbers.	905	floating point numbers.
594		906
595	If the number consists of digits only, JSON::XS will try to	907	If the number consists of digits only, JSON::XS will try to
596	represent it as an integer value. If that fails, it will try to	908	represent it as an integer value. If that fails, it will try to
597	represent it as a numeric (floating point) value if that is possible	909	represent it as a numeric (floating point) value if that is possible
598	without loss of precision. Otherwise it will preserve the number as	910	without loss of precision. Otherwise it will preserve the number as
599	a string value.	911	a string value (in which case you lose roundtripping ability, as the
		912	JSON number will be re-encoded to a JSON string).
600		913
601	Numbers containing a fractional or exponential part will always be	914	Numbers containing a fractional or exponential part will always be
602	represented as numeric (floating point) values, possibly at a loss	915	represented as numeric (floating point) values, possibly at a loss
603	of precision.	916	of precision (in which case you might lose perfect roundtripping
		917	ability, but the JSON number will still be re-encoded as a JSON
		918	number).
604		919
605	This might create round-tripping problems as numbers might become	920	Note that precision is not accuracy - binary floating point values
606	strings, but as Perl is typeless there is no other way to do it.	921	cannot represent most decimal fractions exactly, and when converting
		922	from and to floating point, JSON::XS only guarantees precision up to
		923	but not including the least significant bit.
607		924
608	true, false	925	true, false
609	These JSON atoms become "JSON::XS::true" and "JSON::XS::false",	926	These JSON atoms become "Types::Serialiser::true" and
610	respectively. They are overloaded to act almost exactly like the	927	"Types::Serialiser::false", respectively. They are overloaded to act
611	numbers 1 and 0. You can check whether a scalar is a JSON boolean by	928	almost exactly like the numbers 1 and 0. You can check whether a
612	using the "JSON::XS::is_bool" function.	929	scalar is a JSON boolean by using the "Types::Serialiser::is_bool"
		930	function (after "use Types::Serialier", of course).
613		931
614	null	932	null
615	A JSON null atom becomes "undef" in Perl.	933	A JSON null atom becomes "undef" in Perl.
		934
		935	shell-style comments ("# text")
		936	As a nonstandard extension to the JSON syntax that is enabled by the
		937	"relaxed" setting, shell-style comments are allowed. They can start
		938	anywhere outside strings and go till the end of the line.
		939
		940	tagged values ("(tag)value").
		941	Another nonstandard extension to the JSON syntax, enabled with the
		942	"allow_tags" setting, are tagged values. In this implementation, the
		943	tag must be a perl package/class name encoded as a JSON string,
		944	and the value must be a JSON array encoding optional constructor
		945	arguments.
		946
		947	See "OBJECT SERIALISATION", below, for details.
616		948
617	PERL -> JSON	949	PERL -> JSON
618	The mapping from Perl to JSON is slightly more difficult, as Perl is a	950	The mapping from Perl to JSON is slightly more difficult, as Perl is a
619	truly typeless language, so we can only guess which JSON type is meant	951	truly typeless language, so we can only guess which JSON type is meant
620	by a Perl value.	952	by a Perl value.
621		953
622	hash references	954	hash references
623	Perl hash references become JSON objects. As there is no inherent	955	Perl hash references become JSON objects. As there is no inherent
624	ordering in hash keys (or JSON objects), they will usually be	956	ordering in hash keys (or JSON objects), they will usually be
625	encoded in a pseudo-random order that can change between runs of the	957	encoded in a pseudo-random order. JSON::XS can optionally sort the
626	same program but stays generally the same within a single run of a	958	hash keys (determined by the canonical flag), so the same
627	program. JSON::XS can optionally sort the hash keys (determined by	959	datastructure will serialise to the same JSON text (given same
628	the canonical flag), so the same datastructure will serialise to	960	settings and version of JSON::XS), but this incurs a runtime
629	the same JSON text (given same settings and version of JSON::XS),	961	overhead and is only rarely useful, e.g. when you want to compare
630	but this incurs a runtime overhead and is only rarely useful, e.g.	962	some JSON text against another for equality.
631	when you want to compare some JSON text against another for
632	equality.
633		963
634	array references	964	array references
635	Perl array references become JSON arrays.	965	Perl array references become JSON arrays.
636		966
637	other references	967	other references
638	Other unblessed references are generally not allowed and will cause	968	Other unblessed references are generally not allowed and will cause
639	an exception to be thrown, except for references to the integers 0	969	an exception to be thrown, except for references to the integers 0
640	and 1, which get turned into "false" and "true" atoms in JSON. You	970	and 1, which get turned into "false" and "true" atoms in JSON.
641	can also use "JSON::XS::false" and "JSON::XS::true" to improve	971
		972	Since "JSON::XS" uses the boolean model from Types::Serialiser, you
		973	can also "use Types::Serialiser" and then use
		974	"Types::Serialiser::false" and "Types::Serialiser::true" to improve
642	readability.	975	readability.
643		976
		977	use Types::Serialiser;
644	to_json [\0,JSON::XS::true] # yields [false,true]	978	encode_json [\0, Types::Serialiser::true] # yields [false,true]
645		979
646	JSON::XS::true, JSON::XS::false	980	Types::Serialiser::true, Types::Serialiser::false
647	These special values become JSON true and JSON false values,	981	These special values from the Types::Serialiser module become JSON
648	respectively. You can also use "\1" and "\0" directly if you want.	982	true and JSON false values, respectively. You can also use "\1" and
		983	"\0" directly if you want.
649		984
650	blessed objects	985	blessed objects
651	Blessed objects are not allowed. JSON::XS currently tries to encode	986	Blessed objects are not directly representable in JSON, but
652	their underlying representation (hash- or arrayref), but this	987	"JSON::XS" allows various ways of handling objects. See "OBJECT
653	behaviour might change in future versions.	988	SERIALISATION", below, for details.
654		989
655	simple scalars	990	simple scalars
656	Simple Perl scalars (any scalar that is not a reference) are the	991	Simple Perl scalars (any scalar that is not a reference) are the
657	most difficult objects to encode: JSON::XS will encode undefined	992	most difficult objects to encode: JSON::XS will encode undefined
658	scalars as JSON null value, scalars that have last been used in a	993	scalars as JSON "null" values, scalars that have last been used in a
659	string context before encoding as JSON strings and anything else as	994	string context before encoding as JSON strings, and anything else as
660	number value:	995	number value:
661		996
662	# dump as number	997	# dump as number
663	to_json [2] # yields [2]	998	encode_json [2] # yields [2]
664	to_json [-3.0e17] # yields [-3e+17]	999	encode_json [-3.0e17] # yields [-3e+17]
665	my $value = 5; to_json [$value] # yields [5]	1000	my $value = 5; encode_json [$value] # yields [5]
666		1001
667	# used as string, so dump as string	1002	# used as string, so dump as string
668	print $value;	1003	print $value;
669	to_json [$value] # yields ["5"]	1004	encode_json [$value] # yields ["5"]
670		1005
671	# undef becomes null	1006	# undef becomes null
672	to_json [undef] # yields [null]	1007	encode_json [undef] # yields [null]
673		1008
674	You can force the type to be a JSON string by stringifying it:	1009	You can force the type to be a JSON string by stringifying it:
675		1010
676	my $x = 3.1; # some variable containing a number	1011	my $x = 3.1; # some variable containing a number
677	"$x"; # stringified	1012	"$x"; # stringified
…		…
683	my $x = "3"; # some variable containing a string	1018	my $x = "3"; # some variable containing a string
684	$x += 0; # numify it, ensuring it will be dumped as a number	1019	$x += 0; # numify it, ensuring it will be dumped as a number
685	$x *= 1; # same thing, the choice is yours.	1020	$x *= 1; # same thing, the choice is yours.
686		1021
687	You can not currently force the type in other, less obscure, ways.	1022	You can not currently force the type in other, less obscure, ways.
688	Tell me if you need this capability.	1023	Tell me if you need this capability (but don't forget to explain why
		1024	it's needed :).
689		1025
690	COMPARISON	1026	Note that numerical precision has the same meaning as under Perl (so
691	As already mentioned, this module was created because none of the	1027	binary to decimal conversion follows the same rules as in Perl,
692	existing JSON modules could be made to work correctly. First I will	1028	which can differ to other languages). Also, your perl interpreter
693	describe the problems (or pleasures) I encountered with various existing	1029	might expose extensions to the floating point numbers of your
694	JSON modules, followed by some benchmark values. JSON::XS was designed	1030	platform, such as infinities or NaN's - these cannot be represented
695	not to suffer from any of these problems or limitations.	1031	in JSON, and it is an error to pass those in.
696		1032
697	JSON 1.07	1033	OBJECT SERIALISATION
698	Slow (but very portable, as it is written in pure Perl).	1034	As JSON cannot directly represent Perl objects, you have to choose
		1035	between a pure JSON representation (without the ability to deserialise
		1036	the object automatically again), and a nonstandard extension to the JSON
		1037	syntax, tagged values.
699		1038
700	Undocumented/buggy Unicode handling (how JSON handles Unicode values	1039	SERIALISATION
701	is undocumented. One can get far by feeding it Unicode strings and	1040	What happens when "JSON::XS" encounters a Perl object depends on the
702	doing en-/decoding oneself, but Unicode escapes are not working	1041	"allow_blessed", "convert_blessed" and "allow_tags" settings, which are
		1042	used in this order:
		1043
		1044	1. "allow_tags" is enabled and the object has a "FREEZE" method.
		1045	In this case, "JSON::XS" uses the Types::Serialiser object
		1046	serialisation protocol to create a tagged JSON value, using a
		1047	nonstandard extension to the JSON syntax.
		1048
		1049	This works by invoking the "FREEZE" method on the object, with the
		1050	first argument being the object to serialise, and the second
		1051	argument being the constant string "JSON" to distinguish it from
		1052	other serialisers.
		1053
		1054	The "FREEZE" method can return any number of values (i.e. zero or
		1055	more). These values and the paclkage/classname of the object will
		1056	then be encoded as a tagged JSON value in the following format:
		1057
		1058	("classname")[FREEZE return values...]
		1059
		1060	e.g.:
		1061
		1062	("URI")["http://www.google.com/"]
		1063	("MyDate")[2013,10,29]
		1064	("ImageData::JPEG")["Z3...VlCg=="]
		1065
		1066	For example, the hypothetical "My::Object" "FREEZE" method might use
		1067	the objects "type" and "id" members to encode the object:
		1068
		1069	sub My::Object::FREEZE {
		1070	my ($self, $serialiser) = @_;
		1071
		1072	($self->{type}, $self->{id})
		1073	}
		1074
		1075	2. "convert_blessed" is enabled and the object has a "TO_JSON" method.
		1076	In this case, the "TO_JSON" method of the object is invoked in
		1077	scalar context. It must return a single scalar that can be directly
		1078	encoded into JSON. This scalar replaces the object in the JSON text.
		1079
		1080	For example, the following "TO_JSON" method will convert all URI
		1081	objects to JSON strings when serialised. The fatc that these values
		1082	originally were URI objects is lost.
		1083
		1084	sub URI::TO_JSON {
		1085	my ($uri) = @_;
		1086	$uri->as_string
		1087	}
		1088
		1089	3. "allow_blessed" is enabled.
		1090	The object will be serialised as a JSON null value.
		1091
		1092	4. none of the above
		1093	If none of the settings are enabled or the respective methods are
		1094	missing, "JSON::XS" throws an exception.
		1095
		1096	DESERIALISATION
		1097	For deserialisation there are only two cases to consider: either
		1098	nonstandard tagging was used, in which case "allow_tags" decides, or
		1099	objects cannot be automatically be deserialised, in which case you can
		1100	use postprocessing or the "filter_json_object" or
		1101	"filter_json_single_key_object" callbacks to get some real objects our
		1102	of your JSON.
		1103
		1104	This section only considers the tagged value case: I a tagged JSON
		1105	object is encountered during decoding and "allow_tags" is disabled, a
		1106	parse error will result (as if tagged values were not part of the
		1107	grammar).
		1108
		1109	If "allow_tags" is enabled, "JSON::XS" will look up the "THAW" method of
		1110	the package/classname used during serialisation (it will not attempt to
		1111	load the package as a Perl module). If there is no such method, the
		1112	decoding will fail with an error.
		1113
		1114	Otherwise, the "THAW" method is invoked with the classname as first
		1115	argument, the constant string "JSON" as second argument, and all the
		1116	values from the JSON array (the values originally returned by the
		1117	"FREEZE" method) as remaining arguments.
		1118
		1119	The method must then return the object. While technically you can return
		1120	any Perl scalar, you might have to enable the "enable_nonref" setting to
		1121	make that work in all cases, so better return an actual blessed
		1122	reference.
		1123
		1124	As an example, let's implement a "THAW" function that regenerates the
		1125	"My::Object" from the "FREEZE" example earlier:
		1126
		1127	sub My::Object::THAW {
		1128	my ($class, $serialiser, $type, $id) = @_;
		1129
		1130	$class->new (type => $type, id => $id)
		1131	}
		1132
		1133	ENCODING/CODESET FLAG NOTES
		1134	The interested reader might have seen a number of flags that signify
		1135	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
		1136	some confusion on what these do, so here is a short comparison:
		1137
		1138	"utf8" controls whether the JSON text created by "encode" (and expected
		1139	by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
		1140	control whether "encode" escapes character values outside their
		1141	respective codeset range. Neither of these flags conflict with each
		1142	other, although some combinations make less sense than others.
		1143
		1144	Care has been taken to make all flags symmetrical with respect to
		1145	"encode" and "decode", that is, texts encoded with any combination of
		1146	these flag values will be correctly decoded when the same flags are used
		1147	- in general, if you use different flag settings while encoding vs. when
		1148	decoding you likely have a bug somewhere.
		1149
		1150	Below comes a verbose discussion of these flags. Note that a "codeset"
		1151	is simply an abstract set of character-codepoint pairs, while an
		1152	encoding takes those codepoint numbers and encodes them, in our case
		1153	into octets. Unicode is (among other things) a codeset, UTF-8 is an
		1154	encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets and
		1155	encodings at the same time, which can be confusing.
		1156
		1157	"utf8" flag disabled
		1158	When "utf8" is disabled (the default), then "encode"/"decode"
		1159	generate and expect Unicode strings, that is, characters with high
		1160	ordinal Unicode values (> 255) will be encoded as such characters,
		1161	and likewise such characters are decoded as-is, no changes to them
		1162	will be done, except "(re-)interpreting" them as Unicode codepoints
		1163	or Unicode characters, respectively (to Perl, these are the same
		1164	thing in strings unless you do funny/weird/dumb stuff).
		1165
		1166	This is useful when you want to do the encoding yourself (e.g. when
		1167	you want to have UTF-16 encoded JSON texts) or when some other layer
		1168	does the encoding for you (for example, when printing to a terminal
		1169	using a filehandle that transparently encodes to UTF-8 you certainly
		1170	do NOT want to UTF-8 encode your data first and have Perl encode it
		1171	another time).
		1172
		1173	"utf8" flag enabled
		1174	If the "utf8"-flag is enabled, "encode"/"decode" will encode all
		1175	characters using the corresponding UTF-8 multi-byte sequence, and
		1176	will expect your input strings to be encoded as UTF-8, that is, no
		1177	"character" of the input string must have any value > 255, as UTF-8
		1178	does not allow that.
		1179
		1180	The "utf8" flag therefore switches between two modes: disabled means
		1181	you will get a Unicode string in Perl, enabled means you get an
		1182	UTF-8 encoded octet/binary string in Perl.
		1183
		1184	"latin1" or "ascii" flags enabled
		1185	With "latin1" (or "ascii") enabled, "encode" will escape characters
		1186	with ordinal values > 255 (> 127 with "ascii") and encode the
		1187	remaining characters as specified by the "utf8" flag.
		1188
		1189	If "utf8" is disabled, then the result is also correctly encoded in
		1190	those character sets (as both are proper subsets of Unicode, meaning
		1191	that a Unicode string with all character values < 256 is the same
		1192	thing as a ISO-8859-1 string, and a Unicode string with all
		1193	character values < 128 is the same thing as an ASCII string in
703	properly).	1194	Perl).
704		1195
705	No round-tripping (strings get clobbered if they look like numbers,	1196	If "utf8" is enabled, you still get a correct UTF-8-encoded string,
706	e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that	1197	regardless of these flags, just some more characters will be escaped
707	will decode into the number 2.	1198	using "\uXXXX" then before.
708		1199
709	JSON::PC 0.01	1200	Note that ISO-8859-1-encoded strings are not compatible with UTF-8
710	Very fast.	1201	encoding, while ASCII-encoded strings are. That is because the
		1202	ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
		1203	codeset being a subset of Unicode), while ASCII is.
711		1204
712	Undocumented/buggy Unicode handling.	1205	Surprisingly, "decode" will ignore these flags and so treat all
		1206	input values as governed by the "utf8" flag. If it is disabled, this
		1207	allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
		1208	strict subsets of Unicode. If it is enabled, you can correctly
		1209	decode UTF-8 encoded strings.
713		1210
714	No round-tripping.	1211	So neither "latin1" nor "ascii" are incompatible with the "utf8"
		1212	flag - they only govern when the JSON output engine escapes a
		1213	character or not.
715		1214
716	Has problems handling many Perl values (e.g. regex results and other	1215	The main use for "latin1" is to relatively efficiently store binary
717	magic values will make it croak).	1216	data as JSON, at the expense of breaking compatibility with most
		1217	JSON decoders.
718		1218
719	Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"	1219	The main use for "ascii" is to force the output to not contain
720	which is not a valid JSON text.	1220	characters with values > 127, which means you can interpret the
		1221	resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
		1222	any character set and 8-bit-encoding, and still get the same data
		1223	structure back. This is useful when your channel for JSON transfer
		1224	is not 8-bit clean or the encoding might be mangled in between (e.g.
		1225	in mail), and works because ASCII is a proper subset of most 8-bit
		1226	and multibyte encodings in use in the world.
721		1227
722	Unmaintained (maintainer unresponsive for many months, bugs are not	1228	JSON and ECMAscript
723	getting fixed).	1229	JSON syntax is based on how literals are represented in javascript (the
		1230	not-standardised predecessor of ECMAscript) which is presumably why it
		1231	is called "JavaScript Object Notation".
724		1232
725	JSON::Syck 0.21	1233	However, JSON is not a subset (and also not a superset of course) of
726	Very buggy (often crashes).	1234	ECMAscript (the standard) or javascript (whatever browsers actually
		1235	implement).
727		1236
728	Very inflexible (no human-readable format supported, format pretty	1237	If you want to use javascript's "eval" function to "parse" JSON, you
729	much undocumented. I need at least a format for easy reading by	1238	might run into parse errors for valid JSON texts, or the resulting data
730	humans and a single-line compact format for use in a protocol, and	1239	structure might not be queryable:
731	preferably a way to generate ASCII-only JSON texts).
732		1240
733	Completely broken (and confusingly documented) Unicode handling	1241	One of the problems is that U+2028 and U+2029 are valid characters
734	(Unicode escapes are not working properly, you need to set	1242	inside JSON strings, but are not allowed in ECMAscript string literals,
735	ImplicitUnicode to different values on en- and decoding to get	1243	so the following Perl fragment will not output something that can be
736	symmetric behaviour).	1244	guaranteed to be parsable by javascript's "eval":
737		1245
738	No round-tripping (simple cases work, but this depends on whether	1246	use JSON::XS;
739	the scalar value was used in a numeric context or not).
740		1247
741	Dumping hashes may skip hash values depending on iterator state.	1248	print encode_json [chr 0x2028];
742		1249
743	Unmaintained (maintainer unresponsive for many months, bugs are not	1250	The right fix for this is to use a proper JSON parser in your javascript
744	getting fixed).	1251	programs, and not rely on "eval" (see for example Douglas Crockford's
		1252	json2.js parser).
745		1253
746	Does not check input for validity (i.e. will accept non-JSON input	1254	If this is not an option, you can, as a stop-gap measure, simply encode
747	and return "something" instead of raising an exception. This is a	1255	to ASCII-only JSON:
748	security issue: imagine two banks transferring money between each
749	other using JSON. One bank might parse a given non-JSON request and
750	deduct money, while the other might reject the transaction with a
751	syntax error. While a good protocol will at least recover, that is
752	extra unnecessary work and the transaction will still not succeed).
753		1256
754	JSON::DWIW 0.04	1257	use JSON::XS;
755	Very fast. Very natural. Very nice.
756		1258
757	Undocumented Unicode handling (but the best of the pack. Unicode	1259	print JSON::XS->new->ascii->encode ([chr 0x2028]);
758	escapes still don't get parsed properly).
759		1260
760	Very inflexible.	1261	Note that this will enlarge the resulting JSON text quite a bit if you
		1262	have many non-ASCII characters. You might be tempted to run some regexes
		1263	to only escape U+2028 and U+2029, e.g.:
761		1264
762	No round-tripping.	1265	# DO NOT USE THIS!
		1266	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1267	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1268	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1269	print $json;
763		1270
764	Does not generate valid JSON texts (key strings are often unquoted,	1271	Note that this is a bad idea: the above only works for U+2028 and
765	empty keys result in nothing being output)	1272	U+2029 and thus only for fully ECMAscript-compliant parsers. Many
		1273	existing javascript implementations, however, have issues with other
		1274	characters as well - using "eval" naively simply will cause problems.
766		1275
767	Does not check input for validity.	1276	Another problem is that some javascript implementations reserve some
		1277	property names for their own purposes (which probably makes them
		1278	non-ECMAscript-compliant). For example, Iceweasel reserves the
		1279	"__proto__" property name for its own purposes.
		1280
		1281	If that is a problem, you could parse try to filter the resulting JSON
		1282	output for these property strings, e.g.:
		1283
		1284	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1285
		1286	This works because "__proto__" is not valid outside of strings, so every
		1287	occurrence of ""__proto__"\s*:" must be a string used as property name.
		1288
		1289	If you know of other incompatibilities, please let me know.
768		1290
769	JSON and YAML	1291	JSON and YAML
770	You often hear that JSON is a subset (or a close subset) of YAML. This	1292	You often hear that JSON is a subset of YAML. This is, however, a mass
771	is, however, a mass hysteria and very far from the truth. In general,	1293	hysteria(*) and very far from the truth (as of the time of this
772	there is no way to configure JSON::XS to output a data structure as	1294	writing), so let me state it clearly: *in general, there is no way to
773	valid YAML.	1295	configure JSON::XS to output a data structure as valid YAML* that works
		1296	in all cases.
774		1297
775	If you really must use JSON::XS to generate YAML, you should use this	1298	If you really must use JSON::XS to generate YAML, you should use this
776	algorithm (subject to change in future versions):	1299	algorithm (subject to change in future versions):
777		1300
778	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1301	my $to_yaml = JSON::XS->new->utf8->space_after (1);
779	my $yaml = $to_yaml->encode ($ref) . "\n";	1302	my $yaml = $to_yaml->encode ($ref) . "\n";
780		1303
781	This will usually generate JSON texts that also parse as valid YAML.	1304	This will usually generate JSON texts that also parse as valid YAML.
782	Please note that YAML has hardcoded limits on (simple) object key	1305	Please note that YAML has hardcoded limits on (simple) object key
783	lengths that JSON doesn't have, so you should make sure that your hash	1306	lengths that JSON doesn't have and also has different and incompatible
		1307	unicode character escape syntax, so you should make sure that your hash
784	keys are noticeably shorter than the 1024 characters YAML allows.	1308	keys are noticeably shorter than the 1024 "stream characters" YAML
		1309	allows and that you do not have characters with codepoint values outside
		1310	the Unicode BMP (basic multilingual page). YAML also does not allow "\/"
		1311	sequences in strings (which JSON::XS does not currently generate, but
		1312	other JSON generators might).
785		1313
786	There might be other incompatibilities that I am not aware of. In	1314	There might be other incompatibilities that I am not aware of (or the
		1315	YAML specification has been changed yet again - it does so quite often).
787	general you should not try to generate YAML with a JSON generator or	1316	In general you should not try to generate YAML with a JSON generator or
788	vice versa, or try to parse JSON with a YAML parser or vice versa:	1317	vice versa, or try to parse JSON with a YAML parser or vice versa:
789	chances are high that you will run into severe interoperability	1318	chances are high that you will run into severe interoperability problems
790	problems.	1319	when you least expect it.
		1320
		1321	(*) I have been pressured multiple times by Brian Ingerson (one of the
		1322	authors of the YAML specification) to remove this paragraph, despite
		1323	him acknowledging that the actual incompatibilities exist. As I was
		1324	personally bitten by this "JSON is YAML" lie, I refused and said I
		1325	will continue to educate people about these issues, so others do not
		1326	run into the same problem again and again. After this, Brian called
		1327	me a (quote)complete and worthless idiot(unquote).
		1328
		1329	In my opinion, instead of pressuring and insulting people who
		1330	actually clarify issues with YAML and the wrong statements of some
		1331	of its proponents, I would kindly suggest reading the JSON spec
		1332	(which is not that difficult or long) and finally make YAML
		1333	compatible to it, and educating users about the changes, instead of
		1334	spreading lies about the real compatibility for many years and
		1335	trying to silence people who point out that it isn't true.
		1336
		1337	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON,
		1338	even though the incompatibilities have been documented (and are
		1339	known to Brian) for many years and the spec makes explicit claims
		1340	that YAML is a superset of JSON. It would be so easy to fix, but
		1341	apparently, bullying people and corrupting userdata is so much
		1342	easier.
791		1343
792	SPEED	1344	SPEED
793	It seems that JSON::XS is surprisingly fast, as shown in the following	1345	It seems that JSON::XS is surprisingly fast, as shown in the following
794	tables. They have been generated with the help of the "eg/bench" program	1346	tables. They have been generated with the help of the "eg/bench" program
795	in the JSON::XS distribution, to make it easy to compare on your own	1347	in the JSON::XS distribution, to make it easy to compare on your own
796	system.	1348	system.
797		1349
798	First comes a comparison between various modules using a very short	1350	First comes a comparison between various modules using a very short
799	single-line JSON string:	1351	single-line JSON string (also available at
		1352	<http://dist.schmorp.de/misc/json/short.json>).
800		1353
801	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1354	{"method": "handleMessage", "params": ["user1",
802	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1355	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1356	1, 0]}
803		1357
804	It shows the number of encodes/decodes per second (JSON::XS uses the	1358	It shows the number of encodes/decodes per second (JSON::XS uses the
805	functional interface, while JSON::XS/2 uses the OO interface with	1359	functional interface, while JSON::XS/2 uses the OO interface with
806	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).	1360	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink.
807	Higher is better:	1361	JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses
		1362	the from_json method). Higher is better:
808		1363
809	Storable \| 15779.925 \| 14169.946 \|
810	-----------+------------+------------+
811	module \| encode \| decode \|	1364	module \| encode \| decode \|
812	-----------\|------------\|------------\|	1365	--------------\|------------\|------------\|
813	JSON \| 4990.842 \| 4088.813 \|	1366	JSON::DWIW/DS \| 86302.551 \| 102300.098 \|
814	JSON::DWIW \| 51653.990 \| 71575.154 \|	1367	JSON::DWIW/FJ \| 86302.551 \| 75983.768 \|
815	JSON::PC \| 65948.176 \| 74631.744 \|	1368	JSON::PP \| 15827.562 \| 6638.658 \|
816	JSON::PP \| 8931.652 \| 3817.168 \|	1369	JSON::Syck \| 63358.066 \| 47662.545 \|
817	JSON::Syck \| 24877.248 \| 27776.848 \|	1370	JSON::XS \| 511500.488 \| 511500.488 \|
818	JSON::XS \| 388361.481 \| 227951.304 \|	1371	JSON::XS/2 \| 291271.111 \| 388361.481 \|
819	JSON::XS/2 \| 227951.304 \| 218453.333 \|	1372	JSON::XS/3 \| 361577.931 \| 361577.931 \|
820	JSON::XS/3 \| 338250.323 \| 218453.333 \|	1373	Storable \| 66788.280 \| 265462.278 \|
821	Storable \| 16500.016 \| 135300.129 \|
822	-----------+------------+------------+	1374	--------------+------------+------------+
823		1375
824	That is, JSON::XS is about five times faster than JSON::DWIW on	1376	That is, JSON::XS is almost six times faster than JSON::DWIW on
825	encoding, about three times faster on decoding, and over forty times	1377	encoding, about five times faster on decoding, and over thirty to
826	faster than JSON, even with pretty-printing and key sorting. It also	1378	seventy times faster than JSON's pure perl implementation. It also
827	compares favourably to Storable for small amounts of data.	1379	compares favourably to Storable for small amounts of data.
828		1380
829	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1381	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
830	search API (http://nanoref.com/yahooapis/mgPdGg):	1382	search API (<http://dist.schmorp.de/misc/json/long.json>).
831		1383
832	module \| encode \| decode \|	1384	module \| encode \| decode \|
833	-----------\|------------\|------------\|	1385	--------------\|------------\|------------\|
834	JSON \| 55.260 \| 34.971 \|	1386	JSON::DWIW/DS \| 1647.927 \| 2673.916 \|
835	JSON::DWIW \| 825.228 \| 1082.513 \|	1387	JSON::DWIW/FJ \| 1630.249 \| 2596.128 \|
836	JSON::PC \| 3571.444 \| 2394.829 \|
837	JSON::PP \| 210.987 \| 32.574 \|	1388	JSON::PP \| 400.640 \| 62.311 \|
838	JSON::Syck \| 552.551 \| 787.544 \|	1389	JSON::Syck \| 1481.040 \| 1524.869 \|
839	JSON::XS \| 5780.463 \| 4854.519 \|	1390	JSON::XS \| 20661.596 \| 9541.183 \|
840	JSON::XS/2 \| 3869.998 \| 4798.975 \|	1391	JSON::XS/2 \| 10683.403 \| 9416.938 \|
841	JSON::XS/3 \| 5862.880 \| 4798.975 \|	1392	JSON::XS/3 \| 20661.596 \| 9400.054 \|
842	Storable \| 4445.002 \| 5235.027 \|	1393	Storable \| 19765.806 \| 10000.725 \|
843	-----------+------------+------------+	1394	--------------+------------+------------+
844		1395
845	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1396	Again, JSON::XS leads by far (except for Storable which non-surprisingly
846	decodes faster).	1397	decodes a bit faster).
847		1398
848	On large strings containing lots of high Unicode characters, some	1399	On large strings containing lots of high Unicode characters, some
849	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the	1400	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
850	result will be broken due to missing (or wrong) Unicode handling. Others	1401	result will be broken due to missing (or wrong) Unicode handling. Others
851	refuse to decode or encode properly, so it was impossible to prepare a	1402	refuse to decode or encode properly, so it was impossible to prepare a
…		…
872	Third, JSON::XS recurses using the C stack when decoding objects and	1423	Third, JSON::XS recurses using the C stack when decoding objects and
873	arrays. The C stack is a limited resource: for instance, on my amd64	1424	arrays. The C stack is a limited resource: for instance, on my amd64
874	machine with 8MB of stack size I can decode around 180k nested arrays	1425	machine with 8MB of stack size I can decode around 180k nested arrays
875	but only 14k nested JSON objects (due to perl itself recursing deeply on	1426	but only 14k nested JSON objects (due to perl itself recursing deeply on
876	croak to free the temporary). If that is exceeded, the program crashes.	1427	croak to free the temporary). If that is exceeded, the program crashes.
877	to be conservative, the default nesting limit is set to 512. If your	1428	To be conservative, the default nesting limit is set to 512. If your
878	process has a smaller stack, you should adjust this setting accordingly	1429	process has a smaller stack, you should adjust this setting accordingly
879	with the "max_depth" method.	1430	with the "max_depth" method.
880		1431
881	And last but least, something else could bomb you that I forgot to think	1432	Something else could bomb you, too, that I forgot to think of. In that
882	of. In that case, you get to keep the pieces. I am always open for	1433	case, you get to keep the pieces. I am always open for hints, though...
883	hints, though...	1434
		1435	Also keep in mind that JSON::XS might leak contents of your Perl data
		1436	structures in its error messages, so when you serialise sensitive
		1437	information you might want to make sure that exceptions thrown by
		1438	JSON::XS will not end up in front of untrusted eyes.
884		1439
885	If you are using JSON::XS to return packets to consumption by JavaScript	1440	If you are using JSON::XS to return packets to consumption by JavaScript
886	scripts in a browser you should have a look at	1441	scripts in a browser you should have a look at
887	<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether	1442	<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/>
888	you are vulnerable to some common attack vectors (which really are	1443	to see whether you are vulnerable to some common attack vectors (which
889	browser design bugs, but it is still you who will have to deal with it,	1444	really are browser design bugs, but it is still you who will have to
890	as major browser developers care only for features, not about doing	1445	deal with it, as major browser developers care only for features, not
891	security right).	1446	about getting security right).
		1447
		1448	"OLD" VS. "NEW" JSON (RFC 4627 VS. RFC 7159)
		1449	TL;DR: Due to security concerns, JSON::XS will not allow scalar data in
		1450	JSON texts by default - you need to create your own JSON::XS object and
		1451	enable "allow_nonref":
		1452
		1453	my $json = JSON::XS->new->allow_nonref;
		1454
		1455	$text = $json->encode ($data);
		1456	$data = $json->decode ($text);
		1457
		1458	The long version: JSON being an important and supposedly stable format,
		1459	the IETF standardised it as RFC 4627 in 2006. Unfortunately, the
		1460	inventor of JSON, Dougles Crockford, unilaterally changed the definition
		1461	of JSON in javascript. Rather than create a fork, the IETF decided to
		1462	standardise the new syntax (apparently, so Iw as told, without finding
		1463	it very amusing).
		1464
		1465	The biggest difference between thed original JSON and the new JSON is
		1466	that the new JSON supports scalars (anything other than arrays and
		1467	objects) at the toplevel of a JSON text. While this is strictly
		1468	backwards compatible to older versions, it breaks a number of protocols
		1469	that relied on sending JSON back-to-back, and is a minor security
		1470	concern.
		1471
		1472	For example, imagine you have two banks communicating, and on one side,
		1473	trhe JSON coder gets upgraded. Two messages, such as 10 and 1000 might
		1474	then be confused to mean 101000, something that couldn't happen in the
		1475	original JSON, because niether of these messages would be valid JSON.
		1476
		1477	If one side accepts these messages, then an upgrade in the coder on
		1478	either side could result in this becoming exploitable.
		1479
		1480	This module has always allowed these messages as an optional extension,
		1481	by default disabled. The security concerns are the reason why the
		1482	default is still disabled, but future versions might/will likely upgrade
		1483	to the newer RFC as default format, so you are advised to check your
		1484	implementation and/or override the default with "->allow_nonref (0)" to
		1485	ensure that future versions are safe.
		1486
		1487	INTEROPERABILITY WITH OTHER MODULES
		1488	"JSON::XS" uses the Types::Serialiser module to provide boolean
		1489	constants. That means that the JSON true and false values will be
		1490	comaptible to true and false values of other modules that do the same,
		1491	such as JSON::PP and CBOR::XS.
		1492
		1493	INTEROPERABILITY WITH OTHER JSON DECODERS
		1494	As long as you only serialise data that can be directly expressed in
		1495	JSON, "JSON::XS" is incapable of generating invalid JSON output (modulo
		1496	bugs, but "JSON::XS" has found more bugs in the official JSON testsuite
		1497	(1) than the official JSON testsuite has found in "JSON::XS" (0)).
		1498
		1499	When you have trouble decoding JSON generated by this module using other
		1500	decoders, then it is very likely that you have an encoding mismatch or
		1501	the other decoder is broken.
		1502
		1503	When decoding, "JSON::XS" is strict by default and will likely catch all
		1504	errors. There are currently two settings that change this: "relaxed"
		1505	makes "JSON::XS" accept (but not generate) some non-standard extensions,
		1506	and "allow_tags" will allow you to encode and decode Perl objects, at
		1507	the cost of not outputting valid JSON anymore.
		1508
		1509	TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
		1510	When you use "allow_tags" to use the extended (and also nonstandard and
		1511	invalid) JSON syntax for serialised objects, and you still want to
		1512	decode the generated When you want to serialise objects, you can run a
		1513	regex to replace the tagged syntax by standard JSON arrays (it only
		1514	works for "normal" package names without comma, newlines or single
		1515	colons). First, the readable Perl version:
		1516
		1517	# if your FREEZE methods return no values, you need this replace first:
		1518	$json =~ s/$ \s* (" (?: [^\\":,]+\|\\.\|::)* ") \s* $ \s* \[\s*\]/[$1]/gx;
		1519
		1520	# this works for non-empty constructor arg lists:
		1521	$json =~ s/$ \s* (" (?: [^\\":,]+\|\\.\|::)* ") \s* $ \s* \[/[$1,/gx;
		1522
		1523	And here is a less readable version that is easy to adapt to other
		1524	languages:
		1525
		1526	$json =~ s/$\s("([^\\":,]+\|\\.\|::)")\s$\s\[/[$1,/g;
		1527
		1528	Here is an ECMAScript version (same regex):
		1529
		1530	json = json.replace (/$\s("([^\\":,]+\|\\.\|::)")\s$\s\[/g, "[$1,");
		1531
		1532	Since this syntax converts to standard JSON arrays, it might be hard to
		1533	distinguish serialised objects from normal arrays. You can prepend a
		1534	"magic number" as first array element to reduce chances of a collision:
		1535
		1536	$json =~ s/$\s("([^\\":,]+\|\\.\|::)")\s$\s\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;
		1537
		1538	And after decoding the JSON text, you could walk the data structure
		1539	looking for arrays with a first element of
		1540	"XU1peReLzT4ggEllLanBYq4G9VzliwKF".
		1541
		1542	The same approach can be used to create the tagged format with another
		1543	encoder. First, you create an array with the magic string as first
		1544	member, the classname as second, and constructor arguments last, encode
		1545	it as part of your JSON structure, and then:
		1546
		1547	$json =~ s/\[\s"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s,\s("([^\\":,]+\|\\.\|::)")\s*,/($1)[/g;
		1548
		1549	Again, this has some limitations - the magic string must not be encoded
		1550	with character escapes, and the constructor arguments must be non-empty.
		1551
		1552	RFC7159
		1553	Since this module was written, Google has written a new JSON RFC, RFC
		1554	7159 (and RFC7158). Unfortunately, this RFC breaks compatibility with
		1555	both the original JSON specification on www.json.org and RFC4627.
		1556
		1557	As far as I can see, you can get partial compatibility when parsing by
		1558	using "->allow_nonref". However, consider the security implications of
		1559	doing so.
		1560
		1561	I haven't decided yet when to break compatibility with RFC4627 by
		1562	default (and potentially leave applications insecure) and change the
		1563	default to follow RFC7159, but application authors are well advised to
		1564	call "->allow_nonref(0)" even if this is the current default, if they
		1565	cannot handle non-reference values, in preparation for the day when the
		1566	default will change.
892		1567
893	THREADS	1568	THREADS
894	This module is not guaranteed to be thread safe and there are no plans	1569	This module is not guaranteed to be thread safe and there are no plans
895	to change this until Perl gets thread support (as opposed to the	1570	to change this until Perl gets thread support (as opposed to the
896	horribly slow so-called "threads" which are simply slow and bloated	1571	horribly slow so-called "threads" which are simply slow and bloated
897	process simulations - use fork, its much faster, cheaper, better).	1572	process simulations - use fork, it's much faster, cheaper, better).
898		1573
899	(It might actually work, but you have been warned).	1574	(It might actually work, but you have been warned).
		1575
		1576	THE PERILS OF SETLOCALE
		1577	Sometimes people avoid the Perl locale support and directly call the
		1578	system's setlocale function with "LC_ALL".
		1579
		1580	This breaks both perl and modules such as JSON::XS, as stringification
		1581	of numbers no longer works correctly (e.g. "$x = 0.1; print "$x"+1"
		1582	might print 1, and JSON::XS might output illegal JSON as JSON::XS relies
		1583	on perl to stringify numbers).
		1584
		1585	The solution is simple: don't call "setlocale", or use it for only those
		1586	categories you need, such as "LC_MESSAGES" or "LC_CTYPE".
		1587
		1588	If you need "LC_NUMERIC", you should enable it only around the code that
		1589	actually needs it (avoiding stringification of numbers), and restore it
		1590	afterwards.
900		1591
901	BUGS	1592	BUGS
902	While the goal of this module is to be correct, that unfortunately does	1593	While the goal of this module is to be correct, that unfortunately does
903	not mean its bug-free, only that I think its design is bug-free. It is	1594	not mean it's bug-free, only that I think its design is bug-free. If you
904	still relatively early in its development. If you keep reporting bugs
905	they will be fixed swiftly, though.	1595	keep reporting bugs they will be fixed swiftly, though.
906		1596
907	Please refrain from using rt.cpan.org or any other bug reporting	1597	Please refrain from using rt.cpan.org or any other bug reporting
908	service. I put the contact address into my modules for a reason.	1598	service. I put the contact address into my modules for a reason.
		1599
		1600	SEE ALSO
		1601	The json_xs command line utility for quick experiments.
909		1602
910	AUTHOR	1603	AUTHOR
911	Marc Lehmann <schmorp@schmorp.de>	1604	Marc Lehmann <schmorp@schmorp.de>
912	http://home.schmorp.de/	1605	http://home.schmorp.de/
913		1606

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Comparing JSON-XS/README (file contents): Revision 1.20 by root, Tue Nov 13 22:59:08 2007 UTC vs. Revision 1.41 by root, Wed Nov 16 19:21:53 2016 UTC

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Comparing JSON-XS/README (file contents):
Revision 1.20 by root, Tue Nov 13 22:59:08 2007 UTC vs.
Revision 1.41 by root, Wed Nov 16 19:21:53 2016 UTC