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

Comparing JSON-XS/README (file contents):
Revision 1.21 by root, Tue Dec 4 10:37:42 2007 UTC vs.
Revision 1.38 by root, Tue Oct 29 00:36:18 2013 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);
33	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.
34	To reach the latter goal it was written in C.	33	To reach the latter goal it was written in C.
35		34
36	Beginning with version 2.0 of the JSON module, when both JSON and	35	Beginning with version 2.0 of the JSON module, when both JSON and
37	JSON::XS are installed, then JSON will fall back on JSON::XS (this can	36	JSON::XS are installed, then JSON will fall back on JSON::XS (this can
38	be overriden) with no overhead due to emulation (by inheritign	37	be overridden) with no overhead due to emulation (by inheriting
39	constructor and methods). If JSON::XS is not available, it will fall	38	constructor and methods). If JSON::XS is not available, it will fall
40	back to the compatible JSON::PP module as backend, so using JSON instead	39	back to the compatible JSON::PP module as backend, so using JSON instead
41	of JSON::XS gives you a portable JSON API that can be fast when you need	40	of JSON::XS gives you a portable JSON API that can be fast when you need
42	and doesn't require a C compiler when that is a problem.	41	and doesn't require a C compiler when that is a problem.
43		42
…		…
45	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
46	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
47	cases their maintainers are unresponsive, gone missing, or not listening	46	cases their maintainers are unresponsive, gone missing, or not listening
48	to bug reports for other reasons.	47	to bug reports for other reasons.
49		48
50	See COMPARISON, below, for a comparison to some other JSON modules.
51
52	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
53	vice versa.	50	vice versa.
54		51
55	FEATURES	52	FEATURES
56	* correct Unicode handling	53	* correct Unicode handling
		54
57	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
58	when it does so.	56	does so, and even documents what "correct" means.
59		57
60	* round-trip integrity	58	* round-trip integrity
		59
61	When you serialise a perl data structure using only datatypes	60	When you serialise a perl data structure using only data types
62	supported by JSON, the deserialised data structure is identical on	61	supported by JSON and Perl, the deserialised data structure is
63	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
64	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.
65		66
66	* strict checking of JSON correctness	67	* strict checking of JSON correctness
		68
67	There is no guessing, no generating of illegal JSON texts by	69	There is no guessing, no generating of illegal JSON texts by
68	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
69	is a security feature).	71	is a security feature).
70		72
71	* fast	73	* fast
72	Compared to other JSON modules, this module compares favourably in
73	terms of speed, too.
74		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
75	* simple to use	79	* simple to use
		80
76	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
77	interface.	82	object oriented interface.
78		83
79	* reasonably versatile output formats	84	* reasonably versatile output formats
		85
80	You can choose between the most compact guaranteed single-line	86	You can choose between the most compact guaranteed-single-line
81	format possible (nice for simple line-based protocols), a pure-ascii	87	format possible (nice for simple line-based protocols), a pure-ASCII
82	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
83	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
84	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
85	whatever way you like.	91	whatever way you like.
86		92
87	FUNCTIONAL INTERFACE	93	FUNCTIONAL INTERFACE
88	The following convenience methods are provided by this module. They are	94	The following convenience methods are provided by this module. They are
89	exported by default:	95	exported by default:
90		96
91	$json_text = to_json $perl_scalar	97	$json_text = encode_json $perl_scalar
92	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
93	string (that is, the string contains octets only). Croaks on error.	99	string (that is, the string contains octets only). Croaks on error.
94		100
95	This function call is functionally identical to:	101	This function call is functionally identical to:
96		102
97	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	103	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
98		104
99	except being faster.	105	Except being faster.
100		106
101	$perl_scalar = from_json $json_text	107	$perl_scalar = decode_json $json_text
102	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
103	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
104	resulting reference. Croaks on error.	110	resulting reference. Croaks on error.
105		111
106	This function call is functionally identical to:	112	This function call is functionally identical to:
107		113
108	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	114	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
109		115
110	except being faster.	116	Except being faster.
111
112	$is_boolean = JSON::XS::is_bool $scalar
113	Returns true if the passed scalar represents either JSON::XS::true
114	or JSON::XS::false, two constants that act like 1 and 0,
115	respectively and are used to represent JSON "true" and "false"
116	values in Perl.
117
118	See MAPPING, below, for more information on how JSON values are
119	mapped to Perl.
120		117
121	A FEW NOTES ON UNICODE AND PERL	118	A FEW NOTES ON UNICODE AND PERL
122	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
123	how Unicode works in Perl, modulo bugs.	120	how Unicode works in Perl, modulo bugs.
124		121
125	1. Perl strings can store characters with ordinal values > 255.	122	1. Perl strings can store characters with ordinal values > 255.
126	This enables you to store Unicode characters as single characters in	123	This enables you to store Unicode characters as single characters in
127	a Perl string - very natural.	124	a Perl string - very natural.
128		125
129	2. Perl does not associate an encoding with your strings.	126	2. Perl does not associate an encoding with your strings.
130	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
131	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
132	your string as locale-encoded text, octets/binary, or as Unicode,	129	your string as locale-encoded text, octets/binary, or as Unicode,
133	depending on various settings. In no case is an encoding stored	130	depending on various settings. In no case is an encoding stored
134	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
135	magical metadata.	132	magical meta data.
136		133
137	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
138	of your string.	135	of your string.
139	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
140	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
…		…
145		142
146	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
147	doesn't exist.	144	doesn't exist.
148		145
149	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
150	validly interpreted as a Unicode codepoint.	147	validly interpreted as a Unicode code point.
151	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,
152	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.
153		150
154	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
155	string.	152	string.
…		…
185		182
186	If $enable is false, then the "encode" method will not escape	183	If $enable is false, then the "encode" method will not escape
187	Unicode characters unless required by the JSON syntax or other	184	Unicode characters unless required by the JSON syntax or other
188	flags. This results in a faster and more compact format.	185	flags. This results in a faster and more compact format.
189		186
		187	See also the section ENCODING/CODESET FLAG NOTES later in this
		188	document.
		189
190	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
191	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
192	contain any 8 bit characters.	192	contain any 8 bit characters.
193		193
194	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	194	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
…		…
205	superset of latin1.	205	superset of latin1.
206		206
207	If $enable is false, then the "encode" method will not escape	207	If $enable is false, then the "encode" method will not escape
208	Unicode characters unless required by the JSON syntax or other	208	Unicode characters unless required by the JSON syntax or other
209	flags.	209	flags.
		210
		211	See also the section ENCODING/CODESET FLAG NOTES later in this
		212	document.
210		213
211	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
212	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
213	smaller encoded size. The disadvantage is that the resulting JSON	216	smaller encoded size. The disadvantage is that the resulting JSON
214	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
…		…
234	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
235	string as a (non-encoded) Unicode string, while "decode" expects	238	string as a (non-encoded) Unicode string, while "decode" expects
236	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
237	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.
238		241
		242	See also the section ENCODING/CODESET FLAG NOTES later in this
		243	document.
		244
239	Example, output UTF-16BE-encoded JSON:	245	Example, output UTF-16BE-encoded JSON:
240		246
241	use Encode;	247	use Encode;
242	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	248	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
243		249
…		…
318	If $enable is false (the default), then "decode" will only accept	324	If $enable is false (the default), then "decode" will only accept
319	valid JSON texts.	325	valid JSON texts.
320		326
321	Currently accepted extensions are:	327	Currently accepted extensions are:
322		328
323	* list items can have an end-comma	329	* list items can have an end-comma
		330
324	JSON separates array elements and key-value pairs with commas.	331	JSON separates array elements and key-value pairs with commas.
325	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
326	to be able to quickly append elements, so this extension accepts	333	to be able to quickly append elements, so this extension accepts
327	comma at the end of such items not just between them:	334	comma at the end of such items not just between them:
328		335
…		…
333	{	340	{
334	"k1": "v1",	341	"k1": "v1",
335	"k2": "v2", <- this comma not normally allowed	342	"k2": "v2", <- this comma not normally allowed
336	}	343	}
337		344
338	* shell-style '#'-comments	345	* shell-style '#'-comments
		346
339	Whenever JSON allows whitespace, shell-style comments are	347	Whenever JSON allows whitespace, shell-style comments are
340	additionally allowed. They are terminated by the first	348	additionally allowed. They are terminated by the first
341	carriage-return or line-feed character, after which more	349	carriage-return or line-feed character, after which more
342	white-space and comments are allowed.	350	white-space and comments are allowed.
343		351
…		…
352	output JSON objects by sorting their keys. This is adding a	360	output JSON objects by sorting their keys. This is adding a
353	comparatively high overhead.	361	comparatively high overhead.
354		362
355	If $enable is false, then the "encode" method will output key-value	363	If $enable is false, then the "encode" method will output key-value
356	pairs in the order Perl stores them (which will likely change	364	pairs in the order Perl stores them (which will likely change
357	between runs of the same script).	365	between runs of the same script, and can change even within the same
		366	run from 5.18 onwards).
358		367
359	This option is useful if you want the same data structure to be	368	This option is useful if you want the same data structure to be
360	encoded as the same JSON text (given the same overall settings). If	369	encoded as the same JSON text (given the same overall settings). If
361	it is disabled, the same hash might be encoded differently even if	370	it is disabled, the same hash might be encoded differently even if
362	contains the same data, as key-value pairs have no inherent ordering	371	contains the same data, as key-value pairs have no inherent ordering
363	in Perl.	372	in Perl.
364		373
365	This setting has no effect when decoding JSON texts.	374	This setting has no effect when decoding JSON texts.
		375
		376	This setting has currently no effect on tied hashes.
366		377
367	$json = $json->allow_nonref ([$enable])	378	$json = $json->allow_nonref ([$enable])
368	$enabled = $json->get_allow_nonref	379	$enabled = $json->get_allow_nonref
369	If $enable is true (or missing), then the "encode" method can	380	If $enable is true (or missing), then the "encode" method can
370	convert a non-reference into its corresponding string, number or	381	convert a non-reference into its corresponding string, number or
…		…
380	"allow_nonref", resulting in an invalid JSON text:	391	"allow_nonref", resulting in an invalid JSON text:
381		392
382	JSON::XS->new->allow_nonref->encode ("Hello, World!")	393	JSON::XS->new->allow_nonref->encode ("Hello, World!")
383	=> "Hello, World!"	394	=> "Hello, World!"
384		395
		396	$json = $json->allow_unknown ([$enable])
		397	$enabled = $json->get_allow_unknown
		398	If $enable is true (or missing), then "encode" will not throw an
		399	exception when it encounters values it cannot represent in JSON (for
		400	example, filehandles) but instead will encode a JSON "null" value.
		401	Note that blessed objects are not included here and are handled
		402	separately by c<allow_nonref>.
		403
		404	If $enable is false (the default), then "encode" will throw an
		405	exception when it encounters anything it cannot encode as JSON.
		406
		407	This option does not affect "decode" in any way, and it is
		408	recommended to leave it off unless you know your communications
		409	partner.
		410
385	$json = $json->allow_blessed ([$enable])	411	$json = $json->allow_blessed ([$enable])
386	$enabled = $json->get_allow_blessed	412	$enabled = $json->get_allow_blessed
		413	See "OBJECT SERIALISATION" for details.
		414
387	If $enable is true (or missing), then the "encode" method will not	415	If $enable is true (or missing), then the "encode" method will not
388	barf when it encounters a blessed reference. Instead, the value of	416	barf when it encounters a blessed reference that it cannot convert
389	the convert_blessed option will decide whether "null"	417	otherwise. Instead, a JSON "null" value is encoded instead of the
390	("convert_blessed" disabled or no "TO_JSON" method found) or a	418	object.
391	representation of the object ("convert_blessed" enabled and
392	"TO_JSON" method found) is being encoded. Has no effect on "decode".
393		419
394	If $enable is false (the default), then "encode" will throw an	420	If $enable is false (the default), then "encode" will throw an
395	exception when it encounters a blessed object.	421	exception when it encounters a blessed object that it cannot convert
		422	otherwise.
		423
		424	This setting has no effect on "decode".
396		425
397	$json = $json->convert_blessed ([$enable])	426	$json = $json->convert_blessed ([$enable])
398	$enabled = $json->get_convert_blessed	427	$enabled = $json->get_convert_blessed
		428	See "OBJECT SERIALISATION" for details.
		429
399	If $enable is true (or missing), then "encode", upon encountering a	430	If $enable is true (or missing), then "encode", upon encountering a
400	blessed object, will check for the availability of the "TO_JSON"	431	blessed object, will check for the availability of the "TO_JSON"
401	method on the object's class. If found, it will be called in scalar	432	method on the object's class. If found, it will be called in scalar
402	context and the resulting scalar will be encoded instead of the	433	context and the resulting scalar will be encoded instead of the
403	object. If no "TO_JSON" method is found, the value of	434	object.
404	"allow_blessed" will decide what to do.
405		435
406	The "TO_JSON" method may safely call die if it wants. If "TO_JSON"	436	The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
407	returns other blessed objects, those will be handled in the same	437	returns other blessed objects, those will be handled in the same
408	way. "TO_JSON" must take care of not causing an endless recursion	438	way. "TO_JSON" must take care of not causing an endless recursion
409	cycle (== crash) in this case. The name of "TO_JSON" was chosen	439	cycle (== crash) in this case. The name of "TO_JSON" was chosen
410	because other methods called by the Perl core (== not by the user of	440	because other methods called by the Perl core (== not by the user of
411	the object) are usually in upper case letters and to avoid	441	the object) are usually in upper case letters and to avoid
412	collisions with the "to_json" function.	442	collisions with any "to_json" function or method.
413		443
414	This setting does not yet influence "decode" in any way, but in the	444	If $enable is false (the default), then "encode" will not consider
415	future, global hooks might get installed that influence "decode" and	445	this type of conversion.
416	are enabled by this setting.
417		446
418	If $enable is false, then the "allow_blessed" setting will decide	447	This setting has no effect on "decode".
419	what to do when a blessed object is found.	448
		449	$json = $json->allow_tags ([$enable])
		450	$enabled = $json->allow_tags
		451	See "OBJECT SERIALISATION" for details.
		452
		453	If $enable is true (or missing), then "encode", upon encountering a
		454	blessed object, will check for the availability of the "FREEZE"
		455	method on the object's class. If found, it will be used to serialise
		456	the object into a nonstandard tagged JSON value (that JSON decoders
		457	cannot decode).
		458
		459	It also causes "decode" to parse such tagged JSON values and
		460	deserialise them via a call to the "THAW" method.
		461
		462	If $enable is false (the default), then "encode" will not consider
		463	this type of conversion, and tagged JSON values will cause a parse
		464	error in "decode", as if tags were not part of the grammar.
420		465
421	$json = $json->filter_json_object ([$coderef->($hashref)])	466	$json = $json->filter_json_object ([$coderef->($hashref)])
422	When $coderef is specified, it will be called from "decode" each	467	When $coderef is specified, it will be called from "decode" each
423	time it decodes a JSON object. The only argument is a reference to	468	time it decodes a JSON object. The only argument is a reference to
424	the newly-created hash. If the code references returns a single	469	the newly-created hash. If the code references returns a single
…		…
523	saving space.	568	saving space.
524		569
525	$json = $json->max_depth ([$maximum_nesting_depth])	570	$json = $json->max_depth ([$maximum_nesting_depth])
526	$max_depth = $json->get_max_depth	571	$max_depth = $json->get_max_depth
527	Sets the maximum nesting level (default 512) accepted while encoding	572	Sets the maximum nesting level (default 512) accepted while encoding
528	or decoding. If the JSON text or Perl data structure has an equal or	573	or decoding. If a higher nesting level is detected in JSON text or a
529	higher nesting level then this limit, then the encoder and decoder	574	Perl data structure, then the encoder and decoder will stop and
530	will stop and croak at that point.	575	croak at that point.
531		576
532	Nesting level is defined by number of hash- or arrayrefs that the	577	Nesting level is defined by number of hash- or arrayrefs that the
533	encoder needs to traverse to reach a given point or the number of	578	encoder needs to traverse to reach a given point or the number of
534	"{" or "[" characters without their matching closing parenthesis	579	"{" or "[" characters without their matching closing parenthesis
535	crossed to reach a given character in a string.	580	crossed to reach a given character in a string.
536		581
537	Setting the maximum depth to one disallows any nesting, so that	582	Setting the maximum depth to one disallows any nesting, so that
538	ensures that the object is only a single hash/object or array.	583	ensures that the object is only a single hash/object or array.
539		584
540	The argument to "max_depth" will be rounded up to the next highest
541	power of two. If no argument is given, the highest possible setting	585	If no argument is given, the highest possible setting will be used,
542	will be used, which is rarely useful.	586	which is rarely useful.
		587
		588	Note that nesting is implemented by recursion in C. The default
		589	value has been chosen to be as large as typical operating systems
		590	allow without crashing.
543		591
544	See SECURITY CONSIDERATIONS, below, for more info on why this is	592	See SECURITY CONSIDERATIONS, below, for more info on why this is
545	useful.	593	useful.
546		594
547	$json = $json->max_size ([$maximum_string_size])	595	$json = $json->max_size ([$maximum_string_size])
548	$max_size = $json->get_max_size	596	$max_size = $json->get_max_size
549	Set the maximum length a JSON text may have (in bytes) where	597	Set the maximum length a JSON text may have (in bytes) where
550	decoding is being attempted. The default is 0, meaning no limit.	598	decoding is being attempted. The default is 0, meaning no limit.
551	When "decode" is called on a string longer then this number of	599	When "decode" is called on a string that is longer then this many
552	characters it will not attempt to decode the string but throw an	600	bytes, it will not attempt to decode the string but throw an
553	exception. This setting has no effect on "encode" (yet).	601	exception. This setting has no effect on "encode" (yet).
554		602
555	The argument to "max_size" will be rounded up to the next highest
556	power of two (so may be more than requested). If no argument is
557	given, the limit check will be deactivated (same as when 0 is	603	If no argument is given, the limit check will be deactivated (same
558	specified).	604	as when 0 is specified).
559		605
560	See SECURITY CONSIDERATIONS, below, for more info on why this is	606	See SECURITY CONSIDERATIONS, below, for more info on why this is
561	useful.	607	useful.
562		608
563	$json_text = $json->encode ($perl_scalar)	609	$json_text = $json->encode ($perl_scalar)
564	Converts the given Perl data structure (a simple scalar or a	610	Converts the given Perl value or data structure to its JSON
565	reference to a hash or array) to its JSON representation. Simple	611	representation. Croaks on error.
566	scalars will be converted into JSON string or number sequences,
567	while references to arrays become JSON arrays and references to
568	hashes become JSON objects. Undefined Perl values (e.g. "undef")
569	become JSON "null" values. Neither "true" nor "false" values will be
570	generated.
571		612
572	$perl_scalar = $json->decode ($json_text)	613	$perl_scalar = $json->decode ($json_text)
573	The opposite of "encode": expects a JSON text and tries to parse it,	614	The opposite of "encode": expects a JSON text and tries to parse it,
574	returning the resulting simple scalar or reference. Croaks on error.	615	returning the resulting simple scalar or reference. Croaks on error.
575
576	JSON numbers and strings become simple Perl scalars. JSON arrays
577	become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
578	becomes 1, "false" becomes 0 and "null" becomes "undef".
579		616
580	($perl_scalar, $characters) = $json->decode_prefix ($json_text)	617	($perl_scalar, $characters) = $json->decode_prefix ($json_text)
581	This works like the "decode" method, but instead of raising an	618	This works like the "decode" method, but instead of raising an
582	exception when there is trailing garbage after the first JSON	619	exception when there is trailing garbage after the first JSON
583	object, it will silently stop parsing there and return the number of	620	object, it will silently stop parsing there and return the number of
584	characters consumed so far.	621	characters consumed so far.
585		622
586	This is useful if your JSON texts are not delimited by an outer	623	This is useful if your JSON texts are not delimited by an outer
587	protocol (which is not the brightest thing to do in the first place)
588	and you need to know where the JSON text ends.	624	protocol and you need to know where the JSON text ends.
589		625
590	JSON::XS->new->decode_prefix ("[1] the tail")	626	JSON::XS->new->decode_prefix ("[1] the tail")
591	=> ([], 3)	627	=> ([], 3)
		628
		629	INCREMENTAL PARSING
		630	In some cases, there is the need for incremental parsing of JSON texts.
		631	While this module always has to keep both JSON text and resulting Perl
		632	data structure in memory at one time, it does allow you to parse a JSON
		633	stream incrementally. It does so by accumulating text until it has a
		634	full JSON object, which it then can decode. This process is similar to
		635	using "decode_prefix" to see if a full JSON object is available, but is
		636	much more efficient (and can be implemented with a minimum of method
		637	calls).
		638
		639	JSON::XS will only attempt to parse the JSON text once it is sure it has
		640	enough text to get a decisive result, using a very simple but truly
		641	incremental parser. This means that it sometimes won't stop as early as
		642	the full parser, for example, it doesn't detect mismatched parentheses.
		643	The only thing it guarantees is that it starts decoding as soon as a
		644	syntactically valid JSON text has been seen. This means you need to set
		645	resource limits (e.g. "max_size") to ensure the parser will stop parsing
		646	in the presence if syntax errors.
		647
		648	The following methods implement this incremental parser.
		649
		650	[void, scalar or list context] = $json->incr_parse ([$string])
		651	This is the central parsing function. It can both append new text
		652	and extract objects from the stream accumulated so far (both of
		653	these functions are optional).
		654
		655	If $string is given, then this string is appended to the already
		656	existing JSON fragment stored in the $json object.
		657
		658	After that, if the function is called in void context, it will
		659	simply return without doing anything further. This can be used to
		660	add more text in as many chunks as you want.
		661
		662	If the method is called in scalar context, then it will try to
		663	extract exactly one JSON object. If that is successful, it will
		664	return this object, otherwise it will return "undef". If there is a
		665	parse error, this method will croak just as "decode" would do (one
		666	can then use "incr_skip" to skip the erroneous part). This is the
		667	most common way of using the method.
		668
		669	And finally, in list context, it will try to extract as many objects
		670	from the stream as it can find and return them, or the empty list
		671	otherwise. For this to work, there must be no separators between the
		672	JSON objects or arrays, instead they must be concatenated
		673	back-to-back. If an error occurs, an exception will be raised as in
		674	the scalar context case. Note that in this case, any
		675	previously-parsed JSON texts will be lost.
		676
		677	Example: Parse some JSON arrays/objects in a given string and return
		678	them.
		679
		680	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		681
		682	$lvalue_string = $json->incr_text
		683	This method returns the currently stored JSON fragment as an lvalue,
		684	that is, you can manipulate it. This only works when a preceding
		685	call to "incr_parse" in scalar context successfully returned an
		686	object. Under all other circumstances you must not call this
		687	function (I mean it. although in simple tests it might actually
		688	work, it will fail under real world conditions). As a special
		689	exception, you can also call this method before having parsed
		690	anything.
		691
		692	This function is useful in two cases: a) finding the trailing text
		693	after a JSON object or b) parsing multiple JSON objects separated by
		694	non-JSON text (such as commas).
		695
		696	$json->incr_skip
		697	This will reset the state of the incremental parser and will remove
		698	the parsed text from the input buffer so far. This is useful after
		699	"incr_parse" died, in which case the input buffer and incremental
		700	parser state is left unchanged, to skip the text parsed so far and
		701	to reset the parse state.
		702
		703	The difference to "incr_reset" is that only text until the parse
		704	error occurred is removed.
		705
		706	$json->incr_reset
		707	This completely resets the incremental parser, that is, after this
		708	call, it will be as if the parser had never parsed anything.
		709
		710	This is useful if you want to repeatedly parse JSON objects and want
		711	to ignore any trailing data, which means you have to reset the
		712	parser after each successful decode.
		713
		714	LIMITATIONS
		715	All options that affect decoding are supported, except "allow_nonref".
		716	The reason for this is that it cannot be made to work sensibly: JSON
		717	objects and arrays are self-delimited, i.e. you can concatenate them
		718	back to back and still decode them perfectly. This does not hold true
		719	for JSON numbers, however.
		720
		721	For example, is the string 1 a single JSON number, or is it simply the
		722	start of 12? Or is 12 a single JSON number, or the concatenation of 1
		723	and 2? In neither case you can tell, and this is why JSON::XS takes the
		724	conservative route and disallows this case.
		725
		726	EXAMPLES
		727	Some examples will make all this clearer. First, a simple example that
		728	works similarly to "decode_prefix": We want to decode the JSON object at
		729	the start of a string and identify the portion after the JSON object:
		730
		731	my $text = "[1,2,3] hello";
		732
		733	my $json = new JSON::XS;
		734
		735	my $obj = $json->incr_parse ($text)
		736	or die "expected JSON object or array at beginning of string";
		737
		738	my $tail = $json->incr_text;
		739	# $tail now contains " hello"
		740
		741	Easy, isn't it?
		742
		743	Now for a more complicated example: Imagine a hypothetical protocol
		744	where you read some requests from a TCP stream, and each request is a
		745	JSON array, without any separation between them (in fact, it is often
		746	useful to use newlines as "separators", as these get interpreted as
		747	whitespace at the start of the JSON text, which makes it possible to
		748	test said protocol with "telnet"...).
		749
		750	Here is how you'd do it (it is trivial to write this in an event-based
		751	manner):
		752
		753	my $json = new JSON::XS;
		754
		755	# read some data from the socket
		756	while (sysread $socket, my $buf, 4096) {
		757
		758	# split and decode as many requests as possible
		759	for my $request ($json->incr_parse ($buf)) {
		760	# act on the $request
		761	}
		762	}
		763
		764	Another complicated example: Assume you have a string with JSON objects
		765	or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
		766	[3]"). To parse them, we have to skip the commas between the JSON texts,
		767	and here is where the lvalue-ness of "incr_text" comes in useful:
		768
		769	my $text = "[1],[2], [3]";
		770	my $json = new JSON::XS;
		771
		772	# void context, so no parsing done
		773	$json->incr_parse ($text);
		774
		775	# now extract as many objects as possible. note the
		776	# use of scalar context so incr_text can be called.
		777	while (my $obj = $json->incr_parse) {
		778	# do something with $obj
		779
		780	# now skip the optional comma
		781	$json->incr_text =~ s/^ \s* , //x;
		782	}
		783
		784	Now lets go for a very complex example: Assume that you have a gigantic
		785	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		786	but you cannot load it into memory fully (this has actually happened in
		787	the real world :).
		788
		789	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		790	can still help you: You implement a (very simple) array parser and let
		791	JSON decode the array elements, which are all full JSON objects on their
		792	own (this wouldn't work if the array elements could be JSON numbers, for
		793	example):
		794
		795	my $json = new JSON::XS;
		796
		797	# open the monster
		798	open my $fh, "<bigfile.json"
		799	or die "bigfile: $!";
		800
		801	# first parse the initial "["
		802	for (;;) {
		803	sysread $fh, my $buf, 65536
		804	or die "read error: $!";
		805	$json->incr_parse ($buf); # void context, so no parsing
		806
		807	# Exit the loop once we found and removed(!) the initial "[".
		808	# In essence, we are (ab-)using the $json object as a simple scalar
		809	# we append data to.
		810	last if $json->incr_text =~ s/^ \s* \[ //x;
		811	}
		812
		813	# now we have the skipped the initial "[", so continue
		814	# parsing all the elements.
		815	for (;;) {
		816	# in this loop we read data until we got a single JSON object
		817	for (;;) {
		818	if (my $obj = $json->incr_parse) {
		819	# do something with $obj
		820	last;
		821	}
		822
		823	# add more data
		824	sysread $fh, my $buf, 65536
		825	or die "read error: $!";
		826	$json->incr_parse ($buf); # void context, so no parsing
		827	}
		828
		829	# in this loop we read data until we either found and parsed the
		830	# separating "," between elements, or the final "]"
		831	for (;;) {
		832	# first skip whitespace
		833	$json->incr_text =~ s/^\s*//;
		834
		835	# if we find "]", we are done
		836	if ($json->incr_text =~ s/^\]//) {
		837	print "finished.\n";
		838	exit;
		839	}
		840
		841	# if we find ",", we can continue with the next element
		842	if ($json->incr_text =~ s/^,//) {
		843	last;
		844	}
		845
		846	# if we find anything else, we have a parse error!
		847	if (length $json->incr_text) {
		848	die "parse error near ", $json->incr_text;
		849	}
		850
		851	# else add more data
		852	sysread $fh, my $buf, 65536
		853	or die "read error: $!";
		854	$json->incr_parse ($buf); # void context, so no parsing
		855	}
		856
		857	This is a complex example, but most of the complexity comes from the
		858	fact that we are trying to be correct (bear with me if I am wrong, I
		859	never ran the above example :).
592		860
593	MAPPING	861	MAPPING
594	This section describes how JSON::XS maps Perl values to JSON values and	862	This section describes how JSON::XS maps Perl values to JSON values and
595	vice versa. These mappings are designed to "do the right thing" in most	863	vice versa. These mappings are designed to "do the right thing" in most
596	circumstances automatically, preserving round-tripping characteristics	864	circumstances automatically, preserving round-tripping characteristics
…		…
618	A JSON number becomes either an integer, numeric (floating point) or	886	A JSON number becomes either an integer, numeric (floating point) or
619	string scalar in perl, depending on its range and any fractional	887	string scalar in perl, depending on its range and any fractional
620	parts. On the Perl level, there is no difference between those as	888	parts. On the Perl level, there is no difference between those as
621	Perl handles all the conversion details, but an integer may take	889	Perl handles all the conversion details, but an integer may take
622	slightly less memory and might represent more values exactly than	890	slightly less memory and might represent more values exactly than
623	(floating point) numbers.	891	floating point numbers.
624		892
625	If the number consists of digits only, JSON::XS will try to	893	If the number consists of digits only, JSON::XS will try to
626	represent it as an integer value. If that fails, it will try to	894	represent it as an integer value. If that fails, it will try to
627	represent it as a numeric (floating point) value if that is possible	895	represent it as a numeric (floating point) value if that is possible
628	without loss of precision. Otherwise it will preserve the number as	896	without loss of precision. Otherwise it will preserve the number as
629	a string value.	897	a string value (in which case you lose roundtripping ability, as the
		898	JSON number will be re-encoded to a JSON string).
630		899
631	Numbers containing a fractional or exponential part will always be	900	Numbers containing a fractional or exponential part will always be
632	represented as numeric (floating point) values, possibly at a loss	901	represented as numeric (floating point) values, possibly at a loss
633	of precision.	902	of precision (in which case you might lose perfect roundtripping
		903	ability, but the JSON number will still be re-encoded as a JSON
		904	number).
634		905
635	This might create round-tripping problems as numbers might become	906	Note that precision is not accuracy - binary floating point values
636	strings, but as Perl is typeless there is no other way to do it.	907	cannot represent most decimal fractions exactly, and when converting
		908	from and to floating point, JSON::XS only guarantees precision up to
		909	but not including the least significant bit.
637		910
638	true, false	911	true, false
639	These JSON atoms become "JSON::XS::true" and "JSON::XS::false",	912	These JSON atoms become "Types::Serialiser::true" and
640	respectively. They are overloaded to act almost exactly like the	913	"Types::Serialiser::false", respectively. They are overloaded to act
641	numbers 1 and 0. You can check whether a scalar is a JSON boolean by	914	almost exactly like the numbers 1 and 0. You can check whether a
642	using the "JSON::XS::is_bool" function.	915	scalar is a JSON boolean by using the "Types::Serialiser::is_bool"
		916	function (after "use Types::Serialier", of course).
643		917
644	null	918	null
645	A JSON null atom becomes "undef" in Perl.	919	A JSON null atom becomes "undef" in Perl.
		920
		921	shell-style comments ("# text")
		922	As a nonstandard extension to the JSON syntax that is enabled by the
		923	"relaxed" setting, shell-style comments are allowed. They can start
		924	anywhere outside strings and go till the end of the line.
		925
		926	tagged values ("(tag)value").
		927	Another nonstandard extension to the JSON syntax, enabled with the
		928	"allow_tags" setting, are tagged values. In this implementation, the
		929	tag must be a perl package/class name encoded as a JSON string,
		930	and the value must be a JSON array encoding optional constructor
		931	arguments.
		932
		933	See "OBJECT SERIALISATION", below, for details.
646		934
647	PERL -> JSON	935	PERL -> JSON
648	The mapping from Perl to JSON is slightly more difficult, as Perl is a	936	The mapping from Perl to JSON is slightly more difficult, as Perl is a
649	truly typeless language, so we can only guess which JSON type is meant	937	truly typeless language, so we can only guess which JSON type is meant
650	by a Perl value.	938	by a Perl value.
651		939
652	hash references	940	hash references
653	Perl hash references become JSON objects. As there is no inherent	941	Perl hash references become JSON objects. As there is no inherent
654	ordering in hash keys (or JSON objects), they will usually be	942	ordering in hash keys (or JSON objects), they will usually be
655	encoded in a pseudo-random order that can change between runs of the	943	encoded in a pseudo-random order. JSON::XS can optionally sort the
656	same program but stays generally the same within a single run of a	944	hash keys (determined by the canonical flag), so the same
657	program. JSON::XS can optionally sort the hash keys (determined by	945	datastructure will serialise to the same JSON text (given same
658	the canonical flag), so the same datastructure will serialise to	946	settings and version of JSON::XS), but this incurs a runtime
659	the same JSON text (given same settings and version of JSON::XS),	947	overhead and is only rarely useful, e.g. when you want to compare
660	but this incurs a runtime overhead and is only rarely useful, e.g.	948	some JSON text against another for equality.
661	when you want to compare some JSON text against another for
662	equality.
663		949
664	array references	950	array references
665	Perl array references become JSON arrays.	951	Perl array references become JSON arrays.
666		952
667	other references	953	other references
668	Other unblessed references are generally not allowed and will cause	954	Other unblessed references are generally not allowed and will cause
669	an exception to be thrown, except for references to the integers 0	955	an exception to be thrown, except for references to the integers 0
670	and 1, which get turned into "false" and "true" atoms in JSON. You	956	and 1, which get turned into "false" and "true" atoms in JSON.
671	can also use "JSON::XS::false" and "JSON::XS::true" to improve	957
		958	Since "JSON::XS" uses the boolean model from Types::Serialiser, you
		959	can also "use Types::Serialiser" and then use
		960	"Types::Serialiser::false" and "Types::Serialiser::true" to improve
672	readability.	961	readability.
673		962
		963	use Types::Serialiser;
674	to_json [\0,JSON::XS::true] # yields [false,true]	964	encode_json [\0, Types::Serialiser::true] # yields [false,true]
675		965
676	JSON::XS::true, JSON::XS::false	966	Types::Serialiser::true, Types::Serialiser::false
677	These special values become JSON true and JSON false values,	967	These special values from the Types::Serialiser module become JSON
678	respectively. You can also use "\1" and "\0" directly if you want.	968	true and JSON false values, respectively. You can also use "\1" and
		969	"\0" directly if you want.
679		970
680	blessed objects	971	blessed objects
681	Blessed objects are not allowed. JSON::XS currently tries to encode	972	Blessed objects are not directly representable in JSON, but
682	their underlying representation (hash- or arrayref), but this	973	"JSON::XS" allows various ways of handling objects. See "OBJECT
683	behaviour might change in future versions.	974	SERIALISATION", below, for details.
684		975
685	simple scalars	976	simple scalars
686	Simple Perl scalars (any scalar that is not a reference) are the	977	Simple Perl scalars (any scalar that is not a reference) are the
687	most difficult objects to encode: JSON::XS will encode undefined	978	most difficult objects to encode: JSON::XS will encode undefined
688	scalars as JSON null value, scalars that have last been used in a	979	scalars as JSON "null" values, scalars that have last been used in a
689	string context before encoding as JSON strings and anything else as	980	string context before encoding as JSON strings, and anything else as
690	number value:	981	number value:
691		982
692	# dump as number	983	# dump as number
693	to_json [2] # yields [2]	984	encode_json [2] # yields [2]
694	to_json [-3.0e17] # yields [-3e+17]	985	encode_json [-3.0e17] # yields [-3e+17]
695	my $value = 5; to_json [$value] # yields [5]	986	my $value = 5; encode_json [$value] # yields [5]
696		987
697	# used as string, so dump as string	988	# used as string, so dump as string
698	print $value;	989	print $value;
699	to_json [$value] # yields ["5"]	990	encode_json [$value] # yields ["5"]
700		991
701	# undef becomes null	992	# undef becomes null
702	to_json [undef] # yields [null]	993	encode_json [undef] # yields [null]
703		994
704	You can force the type to be a JSON string by stringifying it:	995	You can force the type to be a JSON string by stringifying it:
705		996
706	my $x = 3.1; # some variable containing a number	997	my $x = 3.1; # some variable containing a number
707	"$x"; # stringified	998	"$x"; # stringified
…		…
713	my $x = "3"; # some variable containing a string	1004	my $x = "3"; # some variable containing a string
714	$x += 0; # numify it, ensuring it will be dumped as a number	1005	$x += 0; # numify it, ensuring it will be dumped as a number
715	$x *= 1; # same thing, the choice is yours.	1006	$x *= 1; # same thing, the choice is yours.
716		1007
717	You can not currently force the type in other, less obscure, ways.	1008	You can not currently force the type in other, less obscure, ways.
718	Tell me if you need this capability.	1009	Tell me if you need this capability (but don't forget to explain why
		1010	it's needed :).
719		1011
720	COMPARISON	1012	Note that numerical precision has the same meaning as under Perl (so
721	As already mentioned, this module was created because none of the	1013	binary to decimal conversion follows the same rules as in Perl,
722	existing JSON modules could be made to work correctly. First I will	1014	which can differ to other languages). Also, your perl interpreter
723	describe the problems (or pleasures) I encountered with various existing	1015	might expose extensions to the floating point numbers of your
724	JSON modules, followed by some benchmark values. JSON::XS was designed	1016	platform, such as infinities or NaN's - these cannot be represented
725	not to suffer from any of these problems or limitations.	1017	in JSON, and it is an error to pass those in.
726		1018
727	JSON 1.07	1019	OBJECT SERIALISATION
728	Slow (but very portable, as it is written in pure Perl).	1020	As JSON cannot directly represent Perl objects, you have to choose
		1021	between a pure JSON representation (without the ability to deserialise
		1022	the object automatically again), and a nonstandard extension to the JSON
		1023	syntax, tagged values.
729		1024
730	Undocumented/buggy Unicode handling (how JSON handles Unicode values	1025	SERIALISATION
731	is undocumented. One can get far by feeding it Unicode strings and	1026	What happens when "JSON::XS" encounters a Perl object depends on the
732	doing en-/decoding oneself, but Unicode escapes are not working	1027	"allow_blessed", "convert_blessed" and "allow_tags" settings, which are
		1028	used in this order:
		1029
		1030	1. "allow_tags" is enabled and the object has a "FREEZE" method.
		1031	In this case, "JSON::XS" uses the Types::Serialiser object
		1032	serialisation protocol to create a tagged JSON value, using a
		1033	nonstandard extension to the JSON syntax.
		1034
		1035	This works by invoking the "FREEZE" method on the object, with the
		1036	first argument being the object to serialise, and the second
		1037	argument being the constant string "JSON" to distinguish it from
		1038	other serialisers.
		1039
		1040	The "FREEZE" method can return any number of values (i.e. zero or
		1041	more). These values and the paclkage/classname of the object will
		1042	then be encoded as a tagged JSON value in the following format:
		1043
		1044	("classname")[FREEZE return values...]
		1045
		1046	For example, the hypothetical "My::Object" "FREEZE" method might use
		1047	the objects "type" and "id" members to encode the object:
		1048
		1049	sub My::Object::FREEZE {
		1050	my ($self, $serialiser) = @_;
		1051
		1052	($self->{type}, $self->{id})
		1053	}
		1054
		1055	2. "convert_blessed" is enabled and the object has a "TO_JSON" method.
		1056	In this case, the "TO_JSON" method of the object is invoked in
		1057	scalar context. It must return a single scalar that can be directly
		1058	encoded into JSON. This scalar replaces the object in the JSON text.
		1059
		1060	For example, the following "TO_JSON" method will convert all URI
		1061	objects to JSON strings when serialised. The fatc that these values
		1062	originally were URI objects is lost.
		1063
		1064	sub URI::TO_JSON {
		1065	my ($uri) = @_;
		1066	$uri->as_string
		1067	}
		1068
		1069	3. "allow_blessed" is enabled.
		1070	The object will be serialised as a JSON null value.
		1071
		1072	4. none of the above
		1073	If none of the settings are enabled or the respective methods are
		1074	missing, "JSON::XS" throws an exception.
		1075
		1076	DESERIALISATION
		1077	For deserialisation there are only two cases to consider: either
		1078	nonstandard tagging was used, in which case "allow_tags" decides, or
		1079	objects cannot be automatically be deserialised, in which case you can
		1080	use postprocessing or the "filter_json_object" or
		1081	"filter_json_single_key_object" callbacks to get some real objects our
		1082	of your JSON.
		1083
		1084	This section only considers the tagged value case: I a tagged JSON
		1085	object is encountered during decoding and "allow_tags" is disabled, a
		1086	parse error will result (as if tagged values were not part of the
		1087	grammar).
		1088
		1089	If "allow_tags" is enabled, "JSON::XS" will look up the "THAW" method of
		1090	the package/classname used during serialisation (it will not attempt to
		1091	load the package as a Perl module). If there is no such method, the
		1092	decoding will fail with an error.
		1093
		1094	Otherwise, the "THAW" method is invoked with the classname as first
		1095	argument, the constant string "JSON" as second argument, and all the
		1096	values from the JSON array (the values originally returned by the
		1097	"FREEZE" method) as remaining arguments.
		1098
		1099	The method must then return the object. While technically you can return
		1100	any Perl scalar, you might have to enable the "enable_nonref" setting to
		1101	make that work in all cases, so better return an actual blessed
		1102	reference.
		1103
		1104	As an example, let's implement a "THAW" function that regenerates the
		1105	"My::Object" from the "FREEZE" example earlier:
		1106
		1107	sub My::Object::THAW {
		1108	my ($class, $serialiser, $type, $id) = @_;
		1109
		1110	$class->new (type => $type, id => $id)
		1111	}
		1112
		1113	ENCODING/CODESET FLAG NOTES
		1114	The interested reader might have seen a number of flags that signify
		1115	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
		1116	some confusion on what these do, so here is a short comparison:
		1117
		1118	"utf8" controls whether the JSON text created by "encode" (and expected
		1119	by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
		1120	control whether "encode" escapes character values outside their
		1121	respective codeset range. Neither of these flags conflict with each
		1122	other, although some combinations make less sense than others.
		1123
		1124	Care has been taken to make all flags symmetrical with respect to
		1125	"encode" and "decode", that is, texts encoded with any combination of
		1126	these flag values will be correctly decoded when the same flags are used
		1127	- in general, if you use different flag settings while encoding vs. when
		1128	decoding you likely have a bug somewhere.
		1129
		1130	Below comes a verbose discussion of these flags. Note that a "codeset"
		1131	is simply an abstract set of character-codepoint pairs, while an
		1132	encoding takes those codepoint numbers and encodes them, in our case
		1133	into octets. Unicode is (among other things) a codeset, UTF-8 is an
		1134	encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets and
		1135	encodings at the same time, which can be confusing.
		1136
		1137	"utf8" flag disabled
		1138	When "utf8" is disabled (the default), then "encode"/"decode"
		1139	generate and expect Unicode strings, that is, characters with high
		1140	ordinal Unicode values (> 255) will be encoded as such characters,
		1141	and likewise such characters are decoded as-is, no changes to them
		1142	will be done, except "(re-)interpreting" them as Unicode codepoints
		1143	or Unicode characters, respectively (to Perl, these are the same
		1144	thing in strings unless you do funny/weird/dumb stuff).
		1145
		1146	This is useful when you want to do the encoding yourself (e.g. when
		1147	you want to have UTF-16 encoded JSON texts) or when some other layer
		1148	does the encoding for you (for example, when printing to a terminal
		1149	using a filehandle that transparently encodes to UTF-8 you certainly
		1150	do NOT want to UTF-8 encode your data first and have Perl encode it
		1151	another time).
		1152
		1153	"utf8" flag enabled
		1154	If the "utf8"-flag is enabled, "encode"/"decode" will encode all
		1155	characters using the corresponding UTF-8 multi-byte sequence, and
		1156	will expect your input strings to be encoded as UTF-8, that is, no
		1157	"character" of the input string must have any value > 255, as UTF-8
		1158	does not allow that.
		1159
		1160	The "utf8" flag therefore switches between two modes: disabled means
		1161	you will get a Unicode string in Perl, enabled means you get an
		1162	UTF-8 encoded octet/binary string in Perl.
		1163
		1164	"latin1" or "ascii" flags enabled
		1165	With "latin1" (or "ascii") enabled, "encode" will escape characters
		1166	with ordinal values > 255 (> 127 with "ascii") and encode the
		1167	remaining characters as specified by the "utf8" flag.
		1168
		1169	If "utf8" is disabled, then the result is also correctly encoded in
		1170	those character sets (as both are proper subsets of Unicode, meaning
		1171	that a Unicode string with all character values < 256 is the same
		1172	thing as a ISO-8859-1 string, and a Unicode string with all
		1173	character values < 128 is the same thing as an ASCII string in
733	properly).	1174	Perl).
734		1175
735	No round-tripping (strings get clobbered if they look like numbers,	1176	If "utf8" is enabled, you still get a correct UTF-8-encoded string,
736	e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that	1177	regardless of these flags, just some more characters will be escaped
737	will decode into the number 2.	1178	using "\uXXXX" then before.
738		1179
739	JSON::PC 0.01	1180	Note that ISO-8859-1-encoded strings are not compatible with UTF-8
740	Very fast.	1181	encoding, while ASCII-encoded strings are. That is because the
		1182	ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
		1183	codeset being a subset of Unicode), while ASCII is.
741		1184
742	Undocumented/buggy Unicode handling.	1185	Surprisingly, "decode" will ignore these flags and so treat all
		1186	input values as governed by the "utf8" flag. If it is disabled, this
		1187	allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
		1188	strict subsets of Unicode. If it is enabled, you can correctly
		1189	decode UTF-8 encoded strings.
743		1190
744	No round-tripping.	1191	So neither "latin1" nor "ascii" are incompatible with the "utf8"
		1192	flag - they only govern when the JSON output engine escapes a
		1193	character or not.
745		1194
746	Has problems handling many Perl values (e.g. regex results and other	1195	The main use for "latin1" is to relatively efficiently store binary
747	magic values will make it croak).	1196	data as JSON, at the expense of breaking compatibility with most
		1197	JSON decoders.
748		1198
749	Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"	1199	The main use for "ascii" is to force the output to not contain
750	which is not a valid JSON text.	1200	characters with values > 127, which means you can interpret the
		1201	resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
		1202	any character set and 8-bit-encoding, and still get the same data
		1203	structure back. This is useful when your channel for JSON transfer
		1204	is not 8-bit clean or the encoding might be mangled in between (e.g.
		1205	in mail), and works because ASCII is a proper subset of most 8-bit
		1206	and multibyte encodings in use in the world.
751		1207
752	Unmaintained (maintainer unresponsive for many months, bugs are not	1208	JSON and ECMAscript
753	getting fixed).	1209	JSON syntax is based on how literals are represented in javascript (the
		1210	not-standardised predecessor of ECMAscript) which is presumably why it
		1211	is called "JavaScript Object Notation".
754		1212
755	JSON::Syck 0.21	1213	However, JSON is not a subset (and also not a superset of course) of
756	Very buggy (often crashes).	1214	ECMAscript (the standard) or javascript (whatever browsers actually
		1215	implement).
757		1216
758	Very inflexible (no human-readable format supported, format pretty	1217	If you want to use javascript's "eval" function to "parse" JSON, you
759	much undocumented. I need at least a format for easy reading by	1218	might run into parse errors for valid JSON texts, or the resulting data
760	humans and a single-line compact format for use in a protocol, and	1219	structure might not be queryable:
761	preferably a way to generate ASCII-only JSON texts).
762		1220
763	Completely broken (and confusingly documented) Unicode handling	1221	One of the problems is that U+2028 and U+2029 are valid characters
764	(Unicode escapes are not working properly, you need to set	1222	inside JSON strings, but are not allowed in ECMAscript string literals,
765	ImplicitUnicode to different values on en- and decoding to get	1223	so the following Perl fragment will not output something that can be
766	symmetric behaviour).	1224	guaranteed to be parsable by javascript's "eval":
767		1225
768	No round-tripping (simple cases work, but this depends on whether	1226	use JSON::XS;
769	the scalar value was used in a numeric context or not).
770		1227
771	Dumping hashes may skip hash values depending on iterator state.	1228	print encode_json [chr 0x2028];
772		1229
773	Unmaintained (maintainer unresponsive for many months, bugs are not	1230	The right fix for this is to use a proper JSON parser in your javascript
774	getting fixed).	1231	programs, and not rely on "eval" (see for example Douglas Crockford's
		1232	json2.js parser).
775		1233
776	Does not check input for validity (i.e. will accept non-JSON input	1234	If this is not an option, you can, as a stop-gap measure, simply encode
777	and return "something" instead of raising an exception. This is a	1235	to ASCII-only JSON:
778	security issue: imagine two banks transferring money between each
779	other using JSON. One bank might parse a given non-JSON request and
780	deduct money, while the other might reject the transaction with a
781	syntax error. While a good protocol will at least recover, that is
782	extra unnecessary work and the transaction will still not succeed).
783		1236
784	JSON::DWIW 0.04	1237	use JSON::XS;
785	Very fast. Very natural. Very nice.
786		1238
787	Undocumented Unicode handling (but the best of the pack. Unicode	1239	print JSON::XS->new->ascii->encode ([chr 0x2028]);
788	escapes still don't get parsed properly).
789		1240
790	Very inflexible.	1241	Note that this will enlarge the resulting JSON text quite a bit if you
		1242	have many non-ASCII characters. You might be tempted to run some regexes
		1243	to only escape U+2028 and U+2029, e.g.:
791		1244
792	No round-tripping.	1245	# DO NOT USE THIS!
		1246	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1247	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1248	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1249	print $json;
793		1250
794	Does not generate valid JSON texts (key strings are often unquoted,	1251	Note that this is a bad idea: the above only works for U+2028 and
795	empty keys result in nothing being output)	1252	U+2029 and thus only for fully ECMAscript-compliant parsers. Many
		1253	existing javascript implementations, however, have issues with other
		1254	characters as well - using "eval" naively simply will cause problems.
796		1255
797	Does not check input for validity.	1256	Another problem is that some javascript implementations reserve some
		1257	property names for their own purposes (which probably makes them
		1258	non-ECMAscript-compliant). For example, Iceweasel reserves the
		1259	"__proto__" property name for its own purposes.
		1260
		1261	If that is a problem, you could parse try to filter the resulting JSON
		1262	output for these property strings, e.g.:
		1263
		1264	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1265
		1266	This works because "__proto__" is not valid outside of strings, so every
		1267	occurrence of ""__proto__"\s*:" must be a string used as property name.
		1268
		1269	If you know of other incompatibilities, please let me know.
798		1270
799	JSON and YAML	1271	JSON and YAML
800	You often hear that JSON is a subset (or a close subset) of YAML. This	1272	You often hear that JSON is a subset of YAML. This is, however, a mass
801	is, however, a mass hysteria and very far from the truth. In general,	1273	hysteria(*) and very far from the truth (as of the time of this
802	there is no way to configure JSON::XS to output a data structure as	1274	writing), so let me state it clearly: *in general, there is no way to
803	valid YAML.	1275	configure JSON::XS to output a data structure as valid YAML* that works
		1276	in all cases.
804		1277
805	If you really must use JSON::XS to generate YAML, you should use this	1278	If you really must use JSON::XS to generate YAML, you should use this
806	algorithm (subject to change in future versions):	1279	algorithm (subject to change in future versions):
807		1280
808	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1281	my $to_yaml = JSON::XS->new->utf8->space_after (1);
809	my $yaml = $to_yaml->encode ($ref) . "\n";	1282	my $yaml = $to_yaml->encode ($ref) . "\n";
810		1283
811	This will usually generate JSON texts that also parse as valid YAML.	1284	This will usually generate JSON texts that also parse as valid YAML.
812	Please note that YAML has hardcoded limits on (simple) object key	1285	Please note that YAML has hardcoded limits on (simple) object key
813	lengths that JSON doesn't have, so you should make sure that your hash	1286	lengths that JSON doesn't have and also has different and incompatible
		1287	unicode character escape syntax, so you should make sure that your hash
814	keys are noticeably shorter than the 1024 characters YAML allows.	1288	keys are noticeably shorter than the 1024 "stream characters" YAML
		1289	allows and that you do not have characters with codepoint values outside
		1290	the Unicode BMP (basic multilingual page). YAML also does not allow "\/"
		1291	sequences in strings (which JSON::XS does not currently generate, but
		1292	other JSON generators might).
815		1293
816	There might be other incompatibilities that I am not aware of. In	1294	There might be other incompatibilities that I am not aware of (or the
		1295	YAML specification has been changed yet again - it does so quite often).
817	general you should not try to generate YAML with a JSON generator or	1296	In general you should not try to generate YAML with a JSON generator or
818	vice versa, or try to parse JSON with a YAML parser or vice versa:	1297	vice versa, or try to parse JSON with a YAML parser or vice versa:
819	chances are high that you will run into severe interoperability	1298	chances are high that you will run into severe interoperability problems
820	problems.	1299	when you least expect it.
		1300
		1301	(*) I have been pressured multiple times by Brian Ingerson (one of the
		1302	authors of the YAML specification) to remove this paragraph, despite
		1303	him acknowledging that the actual incompatibilities exist. As I was
		1304	personally bitten by this "JSON is YAML" lie, I refused and said I
		1305	will continue to educate people about these issues, so others do not
		1306	run into the same problem again and again. After this, Brian called
		1307	me a (quote)complete and worthless idiot(unquote).
		1308
		1309	In my opinion, instead of pressuring and insulting people who
		1310	actually clarify issues with YAML and the wrong statements of some
		1311	of its proponents, I would kindly suggest reading the JSON spec
		1312	(which is not that difficult or long) and finally make YAML
		1313	compatible to it, and educating users about the changes, instead of
		1314	spreading lies about the real compatibility for many years and
		1315	trying to silence people who point out that it isn't true.
		1316
		1317	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON,
		1318	even though the incompatibilities have been documented (and are
		1319	known to Brian) for many years and the spec makes explicit claims
		1320	that YAML is a superset of JSON. It would be so easy to fix, but
		1321	apparently, bullying people and corrupting userdata is so much
		1322	easier.
821		1323
822	SPEED	1324	SPEED
823	It seems that JSON::XS is surprisingly fast, as shown in the following	1325	It seems that JSON::XS is surprisingly fast, as shown in the following
824	tables. They have been generated with the help of the "eg/bench" program	1326	tables. They have been generated with the help of the "eg/bench" program
825	in the JSON::XS distribution, to make it easy to compare on your own	1327	in the JSON::XS distribution, to make it easy to compare on your own
826	system.	1328	system.
827		1329
828	First comes a comparison between various modules using a very short	1330	First comes a comparison between various modules using a very short
829	single-line JSON string:	1331	single-line JSON string (also available at
		1332	<http://dist.schmorp.de/misc/json/short.json>).
830		1333
831	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1334	{"method": "handleMessage", "params": ["user1",
832	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1335	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1336	1, 0]}
833		1337
834	It shows the number of encodes/decodes per second (JSON::XS uses the	1338	It shows the number of encodes/decodes per second (JSON::XS uses the
835	functional interface, while JSON::XS/2 uses the OO interface with	1339	functional interface, while JSON::XS/2 uses the OO interface with
836	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).	1340	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink.
837	Higher is better:	1341	JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses
		1342	the from_json method). Higher is better:
838		1343
839	module \| encode \| decode \|	1344	module \| encode \| decode \|
840	-----------\|------------\|------------\|	1345	--------------\|------------\|------------\|
841	JSON 1.x \| 4990.842 \| 4088.813 \|	1346	JSON::DWIW/DS \| 86302.551 \| 102300.098 \|
842	JSON::DWIW \| 51653.990 \| 71575.154 \|	1347	JSON::DWIW/FJ \| 86302.551 \| 75983.768 \|
843	JSON::PC \| 65948.176 \| 74631.744 \|	1348	JSON::PP \| 15827.562 \| 6638.658 \|
844	JSON::PP \| 8931.652 \| 3817.168 \|	1349	JSON::Syck \| 63358.066 \| 47662.545 \|
845	JSON::Syck \| 24877.248 \| 27776.848 \|	1350	JSON::XS \| 511500.488 \| 511500.488 \|
846	JSON::XS \| 388361.481 \| 227951.304 \|	1351	JSON::XS/2 \| 291271.111 \| 388361.481 \|
847	JSON::XS/2 \| 227951.304 \| 218453.333 \|	1352	JSON::XS/3 \| 361577.931 \| 361577.931 \|
848	JSON::XS/3 \| 338250.323 \| 218453.333 \|	1353	Storable \| 66788.280 \| 265462.278 \|
849	Storable \| 16500.016 \| 135300.129 \|
850	-----------+------------+------------+	1354	--------------+------------+------------+
851		1355
852	That is, JSON::XS is about five times faster than JSON::DWIW on	1356	That is, JSON::XS is almost six times faster than JSON::DWIW on
853	encoding, about three times faster on decoding, and over forty times	1357	encoding, about five times faster on decoding, and over thirty to
854	faster than JSON, even with pretty-printing and key sorting. It also	1358	seventy times faster than JSON's pure perl implementation. It also
855	compares favourably to Storable for small amounts of data.	1359	compares favourably to Storable for small amounts of data.
856		1360
857	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1361	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
858	search API (http://nanoref.com/yahooapis/mgPdGg):	1362	search API (<http://dist.schmorp.de/misc/json/long.json>).
859		1363
860	module \| encode \| decode \|	1364	module \| encode \| decode \|
861	-----------\|------------\|------------\|	1365	--------------\|------------\|------------\|
862	JSON 1.x \| 55.260 \| 34.971 \|	1366	JSON::DWIW/DS \| 1647.927 \| 2673.916 \|
863	JSON::DWIW \| 825.228 \| 1082.513 \|	1367	JSON::DWIW/FJ \| 1630.249 \| 2596.128 \|
864	JSON::PC \| 3571.444 \| 2394.829 \|
865	JSON::PP \| 210.987 \| 32.574 \|	1368	JSON::PP \| 400.640 \| 62.311 \|
866	JSON::Syck \| 552.551 \| 787.544 \|	1369	JSON::Syck \| 1481.040 \| 1524.869 \|
867	JSON::XS \| 5780.463 \| 4854.519 \|	1370	JSON::XS \| 20661.596 \| 9541.183 \|
868	JSON::XS/2 \| 3869.998 \| 4798.975 \|	1371	JSON::XS/2 \| 10683.403 \| 9416.938 \|
869	JSON::XS/3 \| 5862.880 \| 4798.975 \|	1372	JSON::XS/3 \| 20661.596 \| 9400.054 \|
870	Storable \| 4445.002 \| 5235.027 \|	1373	Storable \| 19765.806 \| 10000.725 \|
871	-----------+------------+------------+	1374	--------------+------------+------------+
872		1375
873	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1376	Again, JSON::XS leads by far (except for Storable which non-surprisingly
874	decodes faster).	1377	decodes a bit faster).
875		1378
876	On large strings containing lots of high Unicode characters, some	1379	On large strings containing lots of high Unicode characters, some
877	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the	1380	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
878	result will be broken due to missing (or wrong) Unicode handling. Others	1381	result will be broken due to missing (or wrong) Unicode handling. Others
879	refuse to decode or encode properly, so it was impossible to prepare a	1382	refuse to decode or encode properly, so it was impossible to prepare a
…		…
900	Third, JSON::XS recurses using the C stack when decoding objects and	1403	Third, JSON::XS recurses using the C stack when decoding objects and
901	arrays. The C stack is a limited resource: for instance, on my amd64	1404	arrays. The C stack is a limited resource: for instance, on my amd64
902	machine with 8MB of stack size I can decode around 180k nested arrays	1405	machine with 8MB of stack size I can decode around 180k nested arrays
903	but only 14k nested JSON objects (due to perl itself recursing deeply on	1406	but only 14k nested JSON objects (due to perl itself recursing deeply on
904	croak to free the temporary). If that is exceeded, the program crashes.	1407	croak to free the temporary). If that is exceeded, the program crashes.
905	to be conservative, the default nesting limit is set to 512. If your	1408	To be conservative, the default nesting limit is set to 512. If your
906	process has a smaller stack, you should adjust this setting accordingly	1409	process has a smaller stack, you should adjust this setting accordingly
907	with the "max_depth" method.	1410	with the "max_depth" method.
908		1411
909	And last but least, something else could bomb you that I forgot to think	1412	Something else could bomb you, too, that I forgot to think of. In that
910	of. In that case, you get to keep the pieces. I am always open for	1413	case, you get to keep the pieces. I am always open for hints, though...
911	hints, though...	1414
		1415	Also keep in mind that JSON::XS might leak contents of your Perl data
		1416	structures in its error messages, so when you serialise sensitive
		1417	information you might want to make sure that exceptions thrown by
		1418	JSON::XS will not end up in front of untrusted eyes.
912		1419
913	If you are using JSON::XS to return packets to consumption by JavaScript	1420	If you are using JSON::XS to return packets to consumption by JavaScript
914	scripts in a browser you should have a look at	1421	scripts in a browser you should have a look at
915	<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether	1422	<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/>
916	you are vulnerable to some common attack vectors (which really are	1423	to see whether you are vulnerable to some common attack vectors (which
917	browser design bugs, but it is still you who will have to deal with it,	1424	really are browser design bugs, but it is still you who will have to
918	as major browser developers care only for features, not about doing	1425	deal with it, as major browser developers care only for features, not
919	security right).	1426	about getting security right).
		1427
		1428	INTEROPERABILITY WITH OTHER MODULES
		1429	"JSON::XS" uses the Types::Serialiser module to provide boolean
		1430	constants. That means that the JSON true and false values will be
		1431	comaptible to true and false values of iother modules that do the same,
		1432	such as JSON::PP and CBOR::XS.
920		1433
921	THREADS	1434	THREADS
922	This module is not guaranteed to be thread safe and there are no plans	1435	This module is not guaranteed to be thread safe and there are no plans
923	to change this until Perl gets thread support (as opposed to the	1436	to change this until Perl gets thread support (as opposed to the
924	horribly slow so-called "threads" which are simply slow and bloated	1437	horribly slow so-called "threads" which are simply slow and bloated
925	process simulations - use fork, its much faster, cheaper, better).	1438	process simulations - use fork, it's much faster, cheaper, better).
926		1439
927	(It might actually work, but you have been warned).	1440	(It might actually work, but you have been warned).
		1441
		1442	THE PERILS OF SETLOCALE
		1443	Sometimes people avoid the Perl locale support and directly call the
		1444	system's setlocale function with "LC_ALL".
		1445
		1446	This breaks both perl and modules such as JSON::XS, as stringification
		1447	of numbers no longer works correctly (e.g. "$x = 0.1; print "$x"+1"
		1448	might print 1, and JSON::XS might output illegal JSON as JSON::XS relies
		1449	on perl to stringify numbers).
		1450
		1451	The solution is simple: don't call "setlocale", or use it for only those
		1452	categories you need, such as "LC_MESSAGES" or "LC_CTYPE".
		1453
		1454	If you need "LC_NUMERIC", you should enable it only around the code that
		1455	actually needs it (avoiding stringification of numbers), and restore it
		1456	afterwards.
928		1457
929	BUGS	1458	BUGS
930	While the goal of this module is to be correct, that unfortunately does	1459	While the goal of this module is to be correct, that unfortunately does
931	not mean its bug-free, only that I think its design is bug-free. It is	1460	not mean it's bug-free, only that I think its design is bug-free. If you
932	still relatively early in its development. If you keep reporting bugs
933	they will be fixed swiftly, though.	1461	keep reporting bugs they will be fixed swiftly, though.
934		1462
935	Please refrain from using rt.cpan.org or any other bug reporting	1463	Please refrain from using rt.cpan.org or any other bug reporting
936	service. I put the contact address into my modules for a reason.	1464	service. I put the contact address into my modules for a reason.
		1465
		1466	SEE ALSO
		1467	The json_xs command line utility for quick experiments.
937		1468
938	AUTHOR	1469	AUTHOR
939	Marc Lehmann <schmorp@schmorp.de>	1470	Marc Lehmann <schmorp@schmorp.de>
940	http://home.schmorp.de/	1471	http://home.schmorp.de/
941		1472

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Comparing JSON-XS/README (file contents): Revision 1.21 by root, Tue Dec 4 10:37:42 2007 UTC vs. Revision 1.38 by root, Tue Oct 29 00:36:18 2013 UTC

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Comparing JSON-XS/README (file contents):
Revision 1.21 by root, Tue Dec 4 10:37:42 2007 UTC vs.
Revision 1.38 by root, Tue Oct 29 00:36:18 2013 UTC