[ViewVC] Diff of: cvs/JSON-XS/XS.pm

Comparing JSON-XS/XS.pm (file contents):
Revision 1.72 by root, Sun Nov 25 19:11:07 2007 UTC vs.
Revision 1.143 by root, Fri Oct 25 20:02:54 2013 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	3	JSON::XS - JSON serialising/deserialising, done correctly and fast
		4
		5	=encoding utf-8
4		6
5	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ	7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
6	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)	8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
7		9
8	=head1 SYNOPSIS	10	=head1 SYNOPSIS
10	use JSON::XS;	12	use JSON::XS;
11		13
12	# exported functions, they croak on error	14	# exported functions, they croak on error
13	# and expect/generate UTF-8	15	# and expect/generate UTF-8
14		16
15	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
16	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
17		19
18	# OO-interface	20	# OO-interface
19		21
20	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
21	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
22	$perl_scalar = $coder->decode ($unicode_json_text);	24	$perl_scalar = $coder->decode ($unicode_json_text);
23		25
		26	# Note that JSON version 2.0 and above will automatically use JSON::XS
		27	# if available, at virtually no speed overhead either, so you should
		28	# be able to just:
		29
		30	use JSON;
		31
		32	# and do the same things, except that you have a pure-perl fallback now.
		33
24	=head1 DESCRIPTION	34	=head1 DESCRIPTION
25		35
26	This module converts Perl data structures to JSON and vice versa. Its	36	This module converts Perl data structures to JSON and vice versa. Its
27	primary goal is to be I<correct> and its secondary goal is to be	37	primary goal is to be I<correct> and its secondary goal is to be
28	I<fast>. To reach the latter goal it was written in C.	38	I<fast>. To reach the latter goal it was written in C.
		39
		40	Beginning with version 2.0 of the JSON module, when both JSON and
		41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
		42	overridden) with no overhead due to emulation (by inheriting constructor
		43	and methods). If JSON::XS is not available, it will fall back to the
		44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
		45	gives you a portable JSON API that can be fast when you need and doesn't
		46	require a C compiler when that is a problem.
29		47
30	As this is the n-th-something JSON module on CPAN, what was the reason	48	As this is the n-th-something JSON module on CPAN, what was the reason
31	to write yet another JSON module? While it seems there are many JSON	49	to write yet another JSON module? While it seems there are many JSON
32	modules, none of them correctly handle all corner cases, and in most cases	50	modules, none of them correctly handle all corner cases, and in most cases
33	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
34	reports for other reasons.	52	reports for other reasons.
35		53
36	See COMPARISON, below, for a comparison to some other JSON modules.
37
38	See MAPPING, below, on how JSON::XS maps perl values to JSON values and	54	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
39	vice versa.	55	vice versa.
40		56
41	=head2 FEATURES	57	=head2 FEATURES
42		58
43	=over 4	59	=over 4
44		60
45	=item * correct Unicode handling	61	=item * correct Unicode handling
46		62
47	This module knows how to handle Unicode, and even documents how and when	63	This module knows how to handle Unicode, documents how and when it does
48	it does so.	64	so, and even documents what "correct" means.
49		65
50	=item * round-trip integrity	66	=item * round-trip integrity
51		67
52	When you serialise a perl data structure using only datatypes supported	68	When you serialise a perl data structure using only data types supported
53	by JSON, the deserialised data structure is identical on the Perl level.	69	by JSON and Perl, the deserialised data structure is identical on the Perl
54	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks	70	level. (e.g. the string "2.0" doesn't suddenly become "2" just because
55	like a number).	71	it looks like a number). There I<are> minor exceptions to this, read the
		72	MAPPING section below to learn about those.
56		73
57	=item * strict checking of JSON correctness	74	=item * strict checking of JSON correctness
58		75
59	There is no guessing, no generating of illegal JSON texts by default,	76	There is no guessing, no generating of illegal JSON texts by default,
60	and only JSON is accepted as input by default (the latter is a security	77	and only JSON is accepted as input by default (the latter is a security
61	feature).	78	feature).
62		79
63	=item * fast	80	=item * fast
64		81
65	Compared to other JSON modules, this module compares favourably in terms	82	Compared to other JSON modules and other serialisers such as Storable,
66	of speed, too.	83	this module usually compares favourably in terms of speed, too.
67		84
68	=item * simple to use	85	=item * simple to use
69		86
70	This module has both a simple functional interface as well as an OO	87	This module has both a simple functional interface as well as an object
71	interface.	88	oriented interface.
72		89
73	=item * reasonably versatile output formats	90	=item * reasonably versatile output formats
74		91
75	You can choose between the most compact guaranteed single-line format	92	You can choose between the most compact guaranteed-single-line format
76	possible (nice for simple line-based protocols), a pure-ascii format	93	possible (nice for simple line-based protocols), a pure-ASCII format
77	(for when your transport is not 8-bit clean, still supports the whole	94	(for when your transport is not 8-bit clean, still supports the whole
78	Unicode range), or a pretty-printed format (for when you want to read that	95	Unicode range), or a pretty-printed format (for when you want to read that
79	stuff). Or you can combine those features in whatever way you like.	96	stuff). Or you can combine those features in whatever way you like.
80		97
81	=back	98	=back
82		99
83	=cut	100	=cut
84		101
85	package JSON::XS;	102	package JSON::XS;
86		103
87	use strict;	104	use common::sense;
88		105
89	our $VERSION = '1.53';	106	our $VERSION = 2.34;
90	our @ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
91		108
92	our @EXPORT = qw(to_json from_json);	109	our @EXPORT = qw(encode_json decode_json);
93		110
94	use Exporter;	111	use Exporter;
95	use XSLoader;	112	use XSLoader;
96		113
97	=head1 FUNCTIONAL INTERFACE	114	=head1 FUNCTIONAL INTERFACE
…		…
99	The following convenience methods are provided by this module. They are	116	The following convenience methods are provided by this module. They are
100	exported by default:	117	exported by default:
101		118
102	=over 4	119	=over 4
103		120
104	=item $json_text = to_json $perl_scalar	121	=item $json_text = encode_json $perl_scalar
105		122
106	Converts the given Perl data structure to a UTF-8 encoded, binary string	123	Converts the given Perl data structure to a UTF-8 encoded, binary string
107	(that is, the string contains octets only). Croaks on error.	124	(that is, the string contains octets only). Croaks on error.
108		125
109	This function call is functionally identical to:	126	This function call is functionally identical to:
110		127
111	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	128	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
112		129
113	except being faster.	130	Except being faster.
114		131
115	=item $perl_scalar = from_json $json_text	132	=item $perl_scalar = decode_json $json_text
116		133
117	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries	134	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
118	to parse that as an UTF-8 encoded JSON text, returning the resulting	135	to parse that as an UTF-8 encoded JSON text, returning the resulting
119	reference. Croaks on error.	136	reference. Croaks on error.
120		137
121	This function call is functionally identical to:	138	This function call is functionally identical to:
122		139
123	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	140	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
124		141
125	except being faster.	142	Except being faster.
126		143
127	=item $is_boolean = JSON::XS::is_bool $scalar	144	=item $is_boolean = JSON::XS::is_bool $scalar
128		145
129	Returns true if the passed scalar represents either JSON::XS::true or	146	Returns true if the passed scalar represents either JSON::XS::true or
130	JSON::XS::false, two constants that act like C<1> and C<0>, respectively	147	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
…		…
148	This enables you to store Unicode characters as single characters in a	165	This enables you to store Unicode characters as single characters in a
149	Perl string - very natural.	166	Perl string - very natural.
150		167
151	=item 2. Perl does I<not> associate an encoding with your strings.	168	=item 2. Perl does I<not> associate an encoding with your strings.
152		169
153	Unless you force it to, e.g. when matching it against a regex, or printing	170	... until you force it to, e.g. when matching it against a regex, or
154	the scalar to a file, in which case Perl either interprets your string as	171	printing the scalar to a file, in which case Perl either interprets your
155	locale-encoded text, octets/binary, or as Unicode, depending on various	172	string as locale-encoded text, octets/binary, or as Unicode, depending
156	settings. In no case is an encoding stored together with your data, it is	173	on various settings. In no case is an encoding stored together with your
157	I<use> that decides encoding, not any magical metadata.	174	data, it is I<use> that decides encoding, not any magical meta data.
158		175
159	=item 3. The internal utf-8 flag has no meaning with regards to the	176	=item 3. The internal utf-8 flag has no meaning with regards to the
160	encoding of your string.	177	encoding of your string.
161		178
162	Just ignore that flag unless you debug a Perl bug, a module written in	179	Just ignore that flag unless you debug a Perl bug, a module written in
…		…
168		185
169	If you didn't know about that flag, just the better, pretend it doesn't	186	If you didn't know about that flag, just the better, pretend it doesn't
170	exist.	187	exist.
171		188
172	=item 4. A "Unicode String" is simply a string where each character can be	189	=item 4. A "Unicode String" is simply a string where each character can be
173	validly interpreted as a Unicode codepoint.	190	validly interpreted as a Unicode code point.
174		191
175	If you have UTF-8 encoded data, it is no longer a Unicode string, but a	192	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
176	Unicode string encoded in UTF-8, giving you a binary string.	193	Unicode string encoded in UTF-8, giving you a binary string.
177		194
178	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.	195	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
…		…
216		233
217	If C<$enable> is false, then the C<encode> method will not escape Unicode	234	If C<$enable> is false, then the C<encode> method will not escape Unicode
218	characters unless required by the JSON syntax or other flags. This results	235	characters unless required by the JSON syntax or other flags. This results
219	in a faster and more compact format.	236	in a faster and more compact format.
220		237
		238	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		239	document.
		240
221	The main use for this flag is to produce JSON texts that can be	241	The main use for this flag is to produce JSON texts that can be
222	transmitted over a 7-bit channel, as the encoded JSON texts will not	242	transmitted over a 7-bit channel, as the encoded JSON texts will not
223	contain any 8 bit characters.	243	contain any 8 bit characters.
224		244
225	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	245	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
…		…
236	will not be affected in any way by this flag, as C<decode> by default	256	will not be affected in any way by this flag, as C<decode> by default
237	expects Unicode, which is a strict superset of latin1.	257	expects Unicode, which is a strict superset of latin1.
238		258
239	If C<$enable> is false, then the C<encode> method will not escape Unicode	259	If C<$enable> is false, then the C<encode> method will not escape Unicode
240	characters unless required by the JSON syntax or other flags.	260	characters unless required by the JSON syntax or other flags.
		261
		262	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		263	document.
241		264
242	The main use for this flag is efficiently encoding binary data as JSON	265	The main use for this flag is efficiently encoding binary data as JSON
243	text, as most octets will not be escaped, resulting in a smaller encoded	266	text, as most octets will not be escaped, resulting in a smaller encoded
244	size. The disadvantage is that the resulting JSON text is encoded	267	size. The disadvantage is that the resulting JSON text is encoded
245	in latin1 (and must correctly be treated as such when storing and	268	in latin1 (and must correctly be treated as such when storing and
…		…
265	If C<$enable> is false, then the C<encode> method will return the JSON	288	If C<$enable> is false, then the C<encode> method will return the JSON
266	string as a (non-encoded) Unicode string, while C<decode> expects thus a	289	string as a (non-encoded) Unicode string, while C<decode> expects thus a
267	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	290	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
268	to be done yourself, e.g. using the Encode module.	291	to be done yourself, e.g. using the Encode module.
269		292
		293	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		294	document.
		295
270	Example, output UTF-16BE-encoded JSON:	296	Example, output UTF-16BE-encoded JSON:
271		297
272	use Encode;	298	use Encode;
273	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	299	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
274		300
…		…
276		302
277	use Encode;	303	use Encode;
278	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);	304	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
279		305
280	=item $json = $json->pretty ([$enable])	306	=item $json = $json->pretty ([$enable])
281
282	=item $enabled = $json->get_pretty
283		307
284	This enables (or disables) all of the C<indent>, C<space_before> and	308	This enables (or disables) all of the C<indent>, C<space_before> and
285	C<space_after> (and in the future possibly more) flags in one call to	309	C<space_after> (and in the future possibly more) flags in one call to
286	generate the most readable (or most compact) form possible.	310	generate the most readable (or most compact) form possible.
287		311
…		…
398	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	422	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
399	by sorting their keys. This is adding a comparatively high overhead.	423	by sorting their keys. This is adding a comparatively high overhead.
400		424
401	If C<$enable> is false, then the C<encode> method will output key-value	425	If C<$enable> is false, then the C<encode> method will output key-value
402	pairs in the order Perl stores them (which will likely change between runs	426	pairs in the order Perl stores them (which will likely change between runs
403	of the same script).	427	of the same script, and can change even within the same run from 5.18
		428	onwards).
404		429
405	This option is useful if you want the same data structure to be encoded as	430	This option is useful if you want the same data structure to be encoded as
406	the same JSON text (given the same overall settings). If it is disabled,	431	the same JSON text (given the same overall settings). If it is disabled,
407	the same hash might be encoded differently even if contains the same data,	432	the same hash might be encoded differently even if contains the same data,
408	as key-value pairs have no inherent ordering in Perl.	433	as key-value pairs have no inherent ordering in Perl.
409		434
410	This setting has no effect when decoding JSON texts.	435	This setting has no effect when decoding JSON texts.
411		436
		437	This setting has currently no effect on tied hashes.
		438
412	=item $json = $json->allow_nonref ([$enable])	439	=item $json = $json->allow_nonref ([$enable])
413		440
414	=item $enabled = $json->get_allow_nonref	441	=item $enabled = $json->get_allow_nonref
415		442
416	If C<$enable> is true (or missing), then the C<encode> method can convert a	443	If C<$enable> is true (or missing), then the C<encode> method can convert a
…		…
427	resulting in an invalid JSON text:	454	resulting in an invalid JSON text:
428		455
429	JSON::XS->new->allow_nonref->encode ("Hello, World!")	456	JSON::XS->new->allow_nonref->encode ("Hello, World!")
430	=> "Hello, World!"	457	=> "Hello, World!"
431		458
		459	=item $json = $json->allow_unknown ([$enable])
		460
		461	=item $enabled = $json->get_allow_unknown
		462
		463	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		464	exception when it encounters values it cannot represent in JSON (for
		465	example, filehandles) but instead will encode a JSON C<null> value. Note
		466	that blessed objects are not included here and are handled separately by
		467	c<allow_nonref>.
		468
		469	If C<$enable> is false (the default), then C<encode> will throw an
		470	exception when it encounters anything it cannot encode as JSON.
		471
		472	This option does not affect C<decode> in any way, and it is recommended to
		473	leave it off unless you know your communications partner.
		474
432	=item $json = $json->allow_blessed ([$enable])	475	=item $json = $json->allow_blessed ([$enable])
433		476
434	=item $enabled = $json->get_allow_bless	477	=item $enabled = $json->get_allow_blessed
435		478
436	If C<$enable> is true (or missing), then the C<encode> method will not	479	If C<$enable> is true (or missing), then the C<encode> method will not
437	barf when it encounters a blessed reference. Instead, the value of the	480	barf when it encounters a blessed reference. Instead, the value of the
438	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>	481	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
439	disabled or no C<to_json> method found) or a representation of the	482	disabled or no C<TO_JSON> method found) or a representation of the
440	object (C<convert_blessed> enabled and C<to_json> method found) is being	483	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
441	encoded. Has no effect on C<decode>.	484	encoded. Has no effect on C<decode>.
442		485
443	If C<$enable> is false (the default), then C<encode> will throw an	486	If C<$enable> is false (the default), then C<encode> will throw an
444	exception when it encounters a blessed object.	487	exception when it encounters a blessed object.
445		488
…		…
457	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>	500	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
458	returns other blessed objects, those will be handled in the same	501	returns other blessed objects, those will be handled in the same
459	way. C<TO_JSON> must take care of not causing an endless recursion cycle	502	way. C<TO_JSON> must take care of not causing an endless recursion cycle
460	(== crash) in this case. The name of C<TO_JSON> was chosen because other	503	(== crash) in this case. The name of C<TO_JSON> was chosen because other
461	methods called by the Perl core (== not by the user of the object) are	504	methods called by the Perl core (== not by the user of the object) are
462	usually in upper case letters and to avoid collisions with the C<to_json>	505	usually in upper case letters and to avoid collisions with any C<to_json>
463	function.	506	function or method.
464		507
465	This setting does not yet influence C<decode> in any way, but in the	508	This setting does not yet influence C<decode> in any way, but in the
466	future, global hooks might get installed that influence C<decode> and are	509	future, global hooks might get installed that influence C<decode> and are
467	enabled by this setting.	510	enabled by this setting.
468		511
…		…
576	=item $json = $json->max_depth ([$maximum_nesting_depth])	619	=item $json = $json->max_depth ([$maximum_nesting_depth])
577		620
578	=item $max_depth = $json->get_max_depth	621	=item $max_depth = $json->get_max_depth
579		622
580	Sets the maximum nesting level (default C<512>) accepted while encoding	623	Sets the maximum nesting level (default C<512>) accepted while encoding
581	or decoding. If the JSON text or Perl data structure has an equal or	624	or decoding. If a higher nesting level is detected in JSON text or a Perl
582	higher nesting level then this limit, then the encoder and decoder will	625	data structure, then the encoder and decoder will stop and croak at that
583	stop and croak at that point.	626	point.
584		627
585	Nesting level is defined by number of hash- or arrayrefs that the encoder	628	Nesting level is defined by number of hash- or arrayrefs that the encoder
586	needs to traverse to reach a given point or the number of C<{> or C<[>	629	needs to traverse to reach a given point or the number of C<{> or C<[>
587	characters without their matching closing parenthesis crossed to reach a	630	characters without their matching closing parenthesis crossed to reach a
588	given character in a string.	631	given character in a string.
589		632
590	Setting the maximum depth to one disallows any nesting, so that ensures	633	Setting the maximum depth to one disallows any nesting, so that ensures
591	that the object is only a single hash/object or array.	634	that the object is only a single hash/object or array.
592		635
593	The argument to C<max_depth> will be rounded up to the next highest power
594	of two. If no argument is given, the highest possible setting will be	636	If no argument is given, the highest possible setting will be used, which
595	used, which is rarely useful.	637	is rarely useful.
		638
		639	Note that nesting is implemented by recursion in C. The default value has
		640	been chosen to be as large as typical operating systems allow without
		641	crashing.
596		642
597	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	643	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
598		644
599	=item $json = $json->max_size ([$maximum_string_size])	645	=item $json = $json->max_size ([$maximum_string_size])
600		646
601	=item $max_size = $json->get_max_size	647	=item $max_size = $json->get_max_size
602		648
603	Set the maximum length a JSON text may have (in bytes) where decoding is	649	Set the maximum length a JSON text may have (in bytes) where decoding is
604	being attempted. The default is C<0>, meaning no limit. When C<decode>	650	being attempted. The default is C<0>, meaning no limit. When C<decode>
605	is called on a string longer then this number of characters it will not	651	is called on a string that is longer then this many bytes, it will not
606	attempt to decode the string but throw an exception. This setting has no	652	attempt to decode the string but throw an exception. This setting has no
607	effect on C<encode> (yet).	653	effect on C<encode> (yet).
608		654
609	The argument to C<max_size> will be rounded up to the next B<highest>	655	If no argument is given, the limit check will be deactivated (same as when
610	power of two (so may be more than requested). If no argument is given, the	656	C<0> is specified).
611	limit check will be deactivated (same as when C<0> is specified).
612		657
613	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	658	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
614		659
615	=item $json_text = $json->encode ($perl_scalar)	660	=item $json_text = $json->encode ($perl_scalar)
616		661
617	Converts the given Perl data structure (a simple scalar or a reference	662	Converts the given Perl value or data structure to its JSON
618	to a hash or array) to its JSON representation. Simple scalars will be	663	representation. Croaks on error.
619	converted into JSON string or number sequences, while references to arrays
620	become JSON arrays and references to hashes become JSON objects. Undefined
621	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
622	nor C<false> values will be generated.
623		664
624	=item $perl_scalar = $json->decode ($json_text)	665	=item $perl_scalar = $json->decode ($json_text)
625		666
626	The opposite of C<encode>: expects a JSON text and tries to parse it,	667	The opposite of C<encode>: expects a JSON text and tries to parse it,
627	returning the resulting simple scalar or reference. Croaks on error.	668	returning the resulting simple scalar or reference. Croaks on error.
628
629	JSON numbers and strings become simple Perl scalars. JSON arrays become
630	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
631	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
632		669
633	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)	670	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
634		671
635	This works like the C<decode> method, but instead of raising an exception	672	This works like the C<decode> method, but instead of raising an exception
636	when there is trailing garbage after the first JSON object, it will	673	when there is trailing garbage after the first JSON object, it will
637	silently stop parsing there and return the number of characters consumed	674	silently stop parsing there and return the number of characters consumed
638	so far.	675	so far.
639		676
640	This is useful if your JSON texts are not delimited by an outer protocol	677	This is useful if your JSON texts are not delimited by an outer protocol
641	(which is not the brightest thing to do in the first place) and you need
642	to know where the JSON text ends.	678	and you need to know where the JSON text ends.
643		679
644	JSON::XS->new->decode_prefix ("[1] the tail")	680	JSON::XS->new->decode_prefix ("[1] the tail")
645	=> ([], 3)	681	=> ([], 3)
646		682
647	=back	683	=back
		684
		685
		686	=head1 INCREMENTAL PARSING
		687
		688	In some cases, there is the need for incremental parsing of JSON
		689	texts. While this module always has to keep both JSON text and resulting
		690	Perl data structure in memory at one time, it does allow you to parse a
		691	JSON stream incrementally. It does so by accumulating text until it has
		692	a full JSON object, which it then can decode. This process is similar to
		693	using C<decode_prefix> to see if a full JSON object is available, but
		694	is much more efficient (and can be implemented with a minimum of method
		695	calls).
		696
		697	JSON::XS will only attempt to parse the JSON text once it is sure it
		698	has enough text to get a decisive result, using a very simple but
		699	truly incremental parser. This means that it sometimes won't stop as
		700	early as the full parser, for example, it doesn't detect mismatched
		701	parentheses. The only thing it guarantees is that it starts decoding as
		702	soon as a syntactically valid JSON text has been seen. This means you need
		703	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		704	parsing in the presence if syntax errors.
		705
		706	The following methods implement this incremental parser.
		707
		708	=over 4
		709
		710	=item [void, scalar or list context] = $json->incr_parse ([$string])
		711
		712	This is the central parsing function. It can both append new text and
		713	extract objects from the stream accumulated so far (both of these
		714	functions are optional).
		715
		716	If C<$string> is given, then this string is appended to the already
		717	existing JSON fragment stored in the C<$json> object.
		718
		719	After that, if the function is called in void context, it will simply
		720	return without doing anything further. This can be used to add more text
		721	in as many chunks as you want.
		722
		723	If the method is called in scalar context, then it will try to extract
		724	exactly I<one> JSON object. If that is successful, it will return this
		725	object, otherwise it will return C<undef>. If there is a parse error,
		726	this method will croak just as C<decode> would do (one can then use
		727	C<incr_skip> to skip the erroneous part). This is the most common way of
		728	using the method.
		729
		730	And finally, in list context, it will try to extract as many objects
		731	from the stream as it can find and return them, or the empty list
		732	otherwise. For this to work, there must be no separators between the JSON
		733	objects or arrays, instead they must be concatenated back-to-back. If
		734	an error occurs, an exception will be raised as in the scalar context
		735	case. Note that in this case, any previously-parsed JSON texts will be
		736	lost.
		737
		738	Example: Parse some JSON arrays/objects in a given string and return
		739	them.
		740
		741	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		742
		743	=item $lvalue_string = $json->incr_text
		744
		745	This method returns the currently stored JSON fragment as an lvalue, that
		746	is, you can manipulate it. This I<only> works when a preceding call to
		747	C<incr_parse> in I<scalar context> successfully returned an object. Under
		748	all other circumstances you must not call this function (I mean it.
		749	although in simple tests it might actually work, it I<will> fail under
		750	real world conditions). As a special exception, you can also call this
		751	method before having parsed anything.
		752
		753	This function is useful in two cases: a) finding the trailing text after a
		754	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		755	(such as commas).
		756
		757	=item $json->incr_skip
		758
		759	This will reset the state of the incremental parser and will remove
		760	the parsed text from the input buffer so far. This is useful after
		761	C<incr_parse> died, in which case the input buffer and incremental parser
		762	state is left unchanged, to skip the text parsed so far and to reset the
		763	parse state.
		764
		765	The difference to C<incr_reset> is that only text until the parse error
		766	occurred is removed.
		767
		768	=item $json->incr_reset
		769
		770	This completely resets the incremental parser, that is, after this call,
		771	it will be as if the parser had never parsed anything.
		772
		773	This is useful if you want to repeatedly parse JSON objects and want to
		774	ignore any trailing data, which means you have to reset the parser after
		775	each successful decode.
		776
		777	=back
		778
		779	=head2 LIMITATIONS
		780
		781	All options that affect decoding are supported, except
		782	C<allow_nonref>. The reason for this is that it cannot be made to work
		783	sensibly: JSON objects and arrays are self-delimited, i.e. you can
		784	concatenate them back to back and still decode them perfectly. This does
		785	not hold true for JSON numbers, however.
		786
		787	For example, is the string C<1> a single JSON number, or is it simply the
		788	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		789	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		790	takes the conservative route and disallows this case.
		791
		792	=head2 EXAMPLES
		793
		794	Some examples will make all this clearer. First, a simple example that
		795	works similarly to C<decode_prefix>: We want to decode the JSON object at
		796	the start of a string and identify the portion after the JSON object:
		797
		798	my $text = "[1,2,3] hello";
		799
		800	my $json = new JSON::XS;
		801
		802	my $obj = $json->incr_parse ($text)
		803	or die "expected JSON object or array at beginning of string";
		804
		805	my $tail = $json->incr_text;
		806	# $tail now contains " hello"
		807
		808	Easy, isn't it?
		809
		810	Now for a more complicated example: Imagine a hypothetical protocol where
		811	you read some requests from a TCP stream, and each request is a JSON
		812	array, without any separation between them (in fact, it is often useful to
		813	use newlines as "separators", as these get interpreted as whitespace at
		814	the start of the JSON text, which makes it possible to test said protocol
		815	with C<telnet>...).
		816
		817	Here is how you'd do it (it is trivial to write this in an event-based
		818	manner):
		819
		820	my $json = new JSON::XS;
		821
		822	# read some data from the socket
		823	while (sysread $socket, my $buf, 4096) {
		824
		825	# split and decode as many requests as possible
		826	for my $request ($json->incr_parse ($buf)) {
		827	# act on the $request
		828	}
		829	}
		830
		831	Another complicated example: Assume you have a string with JSON objects
		832	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		833	[3]>). To parse them, we have to skip the commas between the JSON texts,
		834	and here is where the lvalue-ness of C<incr_text> comes in useful:
		835
		836	my $text = "[1],[2], [3]";
		837	my $json = new JSON::XS;
		838
		839	# void context, so no parsing done
		840	$json->incr_parse ($text);
		841
		842	# now extract as many objects as possible. note the
		843	# use of scalar context so incr_text can be called.
		844	while (my $obj = $json->incr_parse) {
		845	# do something with $obj
		846
		847	# now skip the optional comma
		848	$json->incr_text =~ s/^ \s* , //x;
		849	}
		850
		851	Now lets go for a very complex example: Assume that you have a gigantic
		852	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		853	but you cannot load it into memory fully (this has actually happened in
		854	the real world :).
		855
		856	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		857	can still help you: You implement a (very simple) array parser and let
		858	JSON decode the array elements, which are all full JSON objects on their
		859	own (this wouldn't work if the array elements could be JSON numbers, for
		860	example):
		861
		862	my $json = new JSON::XS;
		863
		864	# open the monster
		865	open my $fh, "<bigfile.json"
		866	or die "bigfile: $!";
		867
		868	# first parse the initial "["
		869	for (;;) {
		870	sysread $fh, my $buf, 65536
		871	or die "read error: $!";
		872	$json->incr_parse ($buf); # void context, so no parsing
		873
		874	# Exit the loop once we found and removed(!) the initial "[".
		875	# In essence, we are (ab-)using the $json object as a simple scalar
		876	# we append data to.
		877	last if $json->incr_text =~ s/^ \s* \[ //x;
		878	}
		879
		880	# now we have the skipped the initial "[", so continue
		881	# parsing all the elements.
		882	for (;;) {
		883	# in this loop we read data until we got a single JSON object
		884	for (;;) {
		885	if (my $obj = $json->incr_parse) {
		886	# do something with $obj
		887	last;
		888	}
		889
		890	# add more data
		891	sysread $fh, my $buf, 65536
		892	or die "read error: $!";
		893	$json->incr_parse ($buf); # void context, so no parsing
		894	}
		895
		896	# in this loop we read data until we either found and parsed the
		897	# separating "," between elements, or the final "]"
		898	for (;;) {
		899	# first skip whitespace
		900	$json->incr_text =~ s/^\s*//;
		901
		902	# if we find "]", we are done
		903	if ($json->incr_text =~ s/^\]//) {
		904	print "finished.\n";
		905	exit;
		906	}
		907
		908	# if we find ",", we can continue with the next element
		909	if ($json->incr_text =~ s/^,//) {
		910	last;
		911	}
		912
		913	# if we find anything else, we have a parse error!
		914	if (length $json->incr_text) {
		915	die "parse error near ", $json->incr_text;
		916	}
		917
		918	# else add more data
		919	sysread $fh, my $buf, 65536
		920	or die "read error: $!";
		921	$json->incr_parse ($buf); # void context, so no parsing
		922	}
		923
		924	This is a complex example, but most of the complexity comes from the fact
		925	that we are trying to be correct (bear with me if I am wrong, I never ran
		926	the above example :).
		927
648		928
649		929
650	=head1 MAPPING	930	=head1 MAPPING
651		931
652	This section describes how JSON::XS maps Perl values to JSON values and	932	This section describes how JSON::XS maps Perl values to JSON values and
…		…
682		962
683	A JSON number becomes either an integer, numeric (floating point) or	963	A JSON number becomes either an integer, numeric (floating point) or
684	string scalar in perl, depending on its range and any fractional parts. On	964	string scalar in perl, depending on its range and any fractional parts. On
685	the Perl level, there is no difference between those as Perl handles all	965	the Perl level, there is no difference between those as Perl handles all
686	the conversion details, but an integer may take slightly less memory and	966	the conversion details, but an integer may take slightly less memory and
687	might represent more values exactly than (floating point) numbers.	967	might represent more values exactly than floating point numbers.
688		968
689	If the number consists of digits only, JSON::XS will try to represent	969	If the number consists of digits only, JSON::XS will try to represent
690	it as an integer value. If that fails, it will try to represent it as	970	it as an integer value. If that fails, it will try to represent it as
691	a numeric (floating point) value if that is possible without loss of	971	a numeric (floating point) value if that is possible without loss of
692	precision. Otherwise it will preserve the number as a string value.	972	precision. Otherwise it will preserve the number as a string value (in
		973	which case you lose roundtripping ability, as the JSON number will be
		974	re-encoded to a JSON string).
693		975
694	Numbers containing a fractional or exponential part will always be	976	Numbers containing a fractional or exponential part will always be
695	represented as numeric (floating point) values, possibly at a loss of	977	represented as numeric (floating point) values, possibly at a loss of
696	precision.	978	precision (in which case you might lose perfect roundtripping ability, but
		979	the JSON number will still be re-encoded as a JSON number).
697		980
698	This might create round-tripping problems as numbers might become strings,	981	Note that precision is not accuracy - binary floating point values cannot
699	but as Perl is typeless there is no other way to do it.	982	represent most decimal fractions exactly, and when converting from and to
		983	floating point, JSON::XS only guarantees precision up to but not including
		984	the least significant bit.
700		985
701	=item true, false	986	=item true, false
702		987
703	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	988	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
704	respectively. They are overloaded to act almost exactly like the numbers	989	respectively. They are overloaded to act almost exactly like the numbers
…		…
720		1005
721	=over 4	1006	=over 4
722		1007
723	=item hash references	1008	=item hash references
724		1009
725	Perl hash references become JSON objects. As there is no inherent ordering	1010	Perl hash references become JSON objects. As there is no inherent
726	in hash keys (or JSON objects), they will usually be encoded in a	1011	ordering in hash keys (or JSON objects), they will usually be encoded
727	pseudo-random order that can change between runs of the same program but	1012	in a pseudo-random order. JSON::XS can optionally sort the hash keys
728	stays generally the same within a single run of a program. JSON::XS can	1013	(determined by the I<canonical> flag), so the same datastructure will
729	optionally sort the hash keys (determined by the I<canonical> flag), so	1014	serialise to the same JSON text (given same settings and version of
730	the same datastructure will serialise to the same JSON text (given same	1015	JSON::XS), but this incurs a runtime overhead and is only rarely useful,
731	settings and version of JSON::XS), but this incurs a runtime overhead	1016	e.g. when you want to compare some JSON text against another for equality.
732	and is only rarely useful, e.g. when you want to compare some JSON text
733	against another for equality.
734		1017
735	=item array references	1018	=item array references
736		1019
737	Perl array references become JSON arrays.	1020	Perl array references become JSON arrays.
738		1021
…		…
741	Other unblessed references are generally not allowed and will cause an	1024	Other unblessed references are generally not allowed and will cause an
742	exception to be thrown, except for references to the integers C<0> and	1025	exception to be thrown, except for references to the integers C<0> and
743	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	1026	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
744	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.	1027	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
745		1028
746	to_json [\0,JSON::XS::true] # yields [false,true]	1029	encode_json [\0, JSON::XS::true] # yields [false,true]
747		1030
748	=item JSON::XS::true, JSON::XS::false	1031	=item JSON::XS::true, JSON::XS::false
749		1032
750	These special values become JSON true and JSON false values,	1033	These special values become JSON true and JSON false values,
751	respectively. You can also use C<\1> and C<\0> directly if you want.	1034	respectively. You can also use C<\1> and C<\0> directly if you want.
752		1035
753	=item blessed objects	1036	=item blessed objects
754		1037
755	Blessed objects are not allowed. JSON::XS currently tries to encode their	1038	Blessed objects are not directly representable in JSON. See the
756	underlying representation (hash- or arrayref), but this behaviour might	1039	C<allow_blessed> and C<convert_blessed> methods on various options on
757	change in future versions.	1040	how to deal with this: basically, you can choose between throwing an
		1041	exception, encoding the reference as if it weren't blessed, or provide
		1042	your own serialiser method.
758		1043
759	=item simple scalars	1044	=item simple scalars
760		1045
761	Simple Perl scalars (any scalar that is not a reference) are the most	1046	Simple Perl scalars (any scalar that is not a reference) are the most
762	difficult objects to encode: JSON::XS will encode undefined scalars as	1047	difficult objects to encode: JSON::XS will encode undefined scalars as
763	JSON null value, scalars that have last been used in a string context	1048	JSON C<null> values, scalars that have last been used in a string context
764	before encoding as JSON strings and anything else as number value:	1049	before encoding as JSON strings, and anything else as number value:
765		1050
766	# dump as number	1051	# dump as number
767	to_json [2] # yields [2]	1052	encode_json [2] # yields [2]
768	to_json [-3.0e17] # yields [-3e+17]	1053	encode_json [-3.0e17] # yields [-3e+17]
769	my $value = 5; to_json [$value] # yields [5]	1054	my $value = 5; encode_json [$value] # yields [5]
770		1055
771	# used as string, so dump as string	1056	# used as string, so dump as string
772	print $value;	1057	print $value;
773	to_json [$value] # yields ["5"]	1058	encode_json [$value] # yields ["5"]
774		1059
775	# undef becomes null	1060	# undef becomes null
776	to_json [undef] # yields [null]	1061	encode_json [undef] # yields [null]
777		1062
778	You can force the type to be a JSON string by stringifying it:	1063	You can force the type to be a JSON string by stringifying it:
779		1064
780	my $x = 3.1; # some variable containing a number	1065	my $x = 3.1; # some variable containing a number
781	"$x"; # stringified	1066	"$x"; # stringified
…		…
787	my $x = "3"; # some variable containing a string	1072	my $x = "3"; # some variable containing a string
788	$x += 0; # numify it, ensuring it will be dumped as a number	1073	$x += 0; # numify it, ensuring it will be dumped as a number
789	$x *= 1; # same thing, the choice is yours.	1074	$x *= 1; # same thing, the choice is yours.
790		1075
791	You can not currently force the type in other, less obscure, ways. Tell me	1076	You can not currently force the type in other, less obscure, ways. Tell me
792	if you need this capability.	1077	if you need this capability (but don't forget to explain why it's needed
		1078	:).
		1079
		1080	Note that numerical precision has the same meaning as under Perl (so
		1081	binary to decimal conversion follows the same rules as in Perl, which
		1082	can differ to other languages). Also, your perl interpreter might expose
		1083	extensions to the floating point numbers of your platform, such as
		1084	infinities or NaN's - these cannot be represented in JSON, and it is an
		1085	error to pass those in.
793		1086
794	=back	1087	=back
795		1088
796		1089
797	=head1 COMPARISON	1090	=head1 ENCODING/CODESET FLAG NOTES
798		1091
799	As already mentioned, this module was created because none of the existing	1092	The interested reader might have seen a number of flags that signify
800	JSON modules could be made to work correctly. First I will describe the	1093	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
801	problems (or pleasures) I encountered with various existing JSON modules,	1094	some confusion on what these do, so here is a short comparison:
802	followed by some benchmark values. JSON::XS was designed not to suffer	1095
803	from any of these problems or limitations.	1096	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1097	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1098	control whether C<encode> escapes character values outside their respective
		1099	codeset range. Neither of these flags conflict with each other, although
		1100	some combinations make less sense than others.
		1101
		1102	Care has been taken to make all flags symmetrical with respect to
		1103	C<encode> and C<decode>, that is, texts encoded with any combination of
		1104	these flag values will be correctly decoded when the same flags are used
		1105	- in general, if you use different flag settings while encoding vs. when
		1106	decoding you likely have a bug somewhere.
		1107
		1108	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1109	simply an abstract set of character-codepoint pairs, while an encoding
		1110	takes those codepoint numbers and I<encodes> them, in our case into
		1111	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1112	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1113	the same time, which can be confusing.
804		1114
805	=over 4	1115	=over 4
806		1116
807	=item JSON 1.07	1117	=item C<utf8> flag disabled
808		1118
809	Slow (but very portable, as it is written in pure Perl).	1119	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1120	and expect Unicode strings, that is, characters with high ordinal Unicode
		1121	values (> 255) will be encoded as such characters, and likewise such
		1122	characters are decoded as-is, no changes to them will be done, except
		1123	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1124	respectively (to Perl, these are the same thing in strings unless you do
		1125	funny/weird/dumb stuff).
810		1126
811	Undocumented/buggy Unicode handling (how JSON handles Unicode values is	1127	This is useful when you want to do the encoding yourself (e.g. when you
812	undocumented. One can get far by feeding it Unicode strings and doing	1128	want to have UTF-16 encoded JSON texts) or when some other layer does
813	en-/decoding oneself, but Unicode escapes are not working properly).	1129	the encoding for you (for example, when printing to a terminal using a
		1130	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1131	to UTF-8 encode your data first and have Perl encode it another time).
814		1132
815	No round-tripping (strings get clobbered if they look like numbers, e.g.	1133	=item C<utf8> flag enabled
816	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
817	decode into the number 2.
818		1134
819	=item JSON::PC 0.01	1135	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1136	characters using the corresponding UTF-8 multi-byte sequence, and will
		1137	expect your input strings to be encoded as UTF-8, that is, no "character"
		1138	of the input string must have any value > 255, as UTF-8 does not allow
		1139	that.
820		1140
821	Very fast.	1141	The C<utf8> flag therefore switches between two modes: disabled means you
		1142	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1143	octet/binary string in Perl.
822		1144
823	Undocumented/buggy Unicode handling.	1145	=item C<latin1> or C<ascii> flags enabled
824		1146
825	No round-tripping.	1147	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1148	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1149	characters as specified by the C<utf8> flag.
826		1150
827	Has problems handling many Perl values (e.g. regex results and other magic	1151	If C<utf8> is disabled, then the result is also correctly encoded in those
828	values will make it croak).	1152	character sets (as both are proper subsets of Unicode, meaning that a
		1153	Unicode string with all character values < 256 is the same thing as a
		1154	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1155	the same thing as an ASCII string in Perl).
829		1156
830	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1157	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
831	which is not a valid JSON text.	1158	regardless of these flags, just some more characters will be escaped using
		1159	C<\uXXXX> then before.
832		1160
833	Unmaintained (maintainer unresponsive for many months, bugs are not	1161	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
834	getting fixed).	1162	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1163	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1164	a subset of Unicode), while ASCII is.
835		1165
836	=item JSON::Syck 0.21	1166	Surprisingly, C<decode> will ignore these flags and so treat all input
		1167	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1168	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1169	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
837		1170
838	Very buggy (often crashes).	1171	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1172	they only govern when the JSON output engine escapes a character or not.
839		1173
840	Very inflexible (no human-readable format supported, format pretty much	1174	The main use for C<latin1> is to relatively efficiently store binary data
841	undocumented. I need at least a format for easy reading by humans and a	1175	as JSON, at the expense of breaking compatibility with most JSON decoders.
842	single-line compact format for use in a protocol, and preferably a way to
843	generate ASCII-only JSON texts).
844		1176
845	Completely broken (and confusingly documented) Unicode handling (Unicode	1177	The main use for C<ascii> is to force the output to not contain characters
846	escapes are not working properly, you need to set ImplicitUnicode to	1178	with values > 127, which means you can interpret the resulting string
847	I<different> values on en- and decoding to get symmetric behaviour).	1179	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
848		1180	8-bit-encoding, and still get the same data structure back. This is useful
849	No round-tripping (simple cases work, but this depends on whether the scalar	1181	when your channel for JSON transfer is not 8-bit clean or the encoding
850	value was used in a numeric context or not).	1182	might be mangled in between (e.g. in mail), and works because ASCII is a
851		1183	proper subset of most 8-bit and multibyte encodings in use in the world.
852	Dumping hashes may skip hash values depending on iterator state.
853
854	Unmaintained (maintainer unresponsive for many months, bugs are not
855	getting fixed).
856
857	Does not check input for validity (i.e. will accept non-JSON input and
858	return "something" instead of raising an exception. This is a security
859	issue: imagine two banks transferring money between each other using
860	JSON. One bank might parse a given non-JSON request and deduct money,
861	while the other might reject the transaction with a syntax error. While a
862	good protocol will at least recover, that is extra unnecessary work and
863	the transaction will still not succeed).
864
865	=item JSON::DWIW 0.04
866
867	Very fast. Very natural. Very nice.
868
869	Undocumented Unicode handling (but the best of the pack. Unicode escapes
870	still don't get parsed properly).
871
872	Very inflexible.
873
874	No round-tripping.
875
876	Does not generate valid JSON texts (key strings are often unquoted, empty keys
877	result in nothing being output)
878
879	Does not check input for validity.
880		1184
881	=back	1185	=back
882		1186
883		1187
		1188	=head2 JSON and ECMAscript
		1189
		1190	JSON syntax is based on how literals are represented in javascript (the
		1191	not-standardised predecessor of ECMAscript) which is presumably why it is
		1192	called "JavaScript Object Notation".
		1193
		1194	However, JSON is not a subset (and also not a superset of course) of
		1195	ECMAscript (the standard) or javascript (whatever browsers actually
		1196	implement).
		1197
		1198	If you want to use javascript's C<eval> function to "parse" JSON, you
		1199	might run into parse errors for valid JSON texts, or the resulting data
		1200	structure might not be queryable:
		1201
		1202	One of the problems is that U+2028 and U+2029 are valid characters inside
		1203	JSON strings, but are not allowed in ECMAscript string literals, so the
		1204	following Perl fragment will not output something that can be guaranteed
		1205	to be parsable by javascript's C<eval>:
		1206
		1207	use JSON::XS;
		1208
		1209	print encode_json [chr 0x2028];
		1210
		1211	The right fix for this is to use a proper JSON parser in your javascript
		1212	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1213	F<json2.js> parser).
		1214
		1215	If this is not an option, you can, as a stop-gap measure, simply encode to
		1216	ASCII-only JSON:
		1217
		1218	use JSON::XS;
		1219
		1220	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1221
		1222	Note that this will enlarge the resulting JSON text quite a bit if you
		1223	have many non-ASCII characters. You might be tempted to run some regexes
		1224	to only escape U+2028 and U+2029, e.g.:
		1225
		1226	# DO NOT USE THIS!
		1227	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1228	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1229	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1230	print $json;
		1231
		1232	Note that I<this is a bad idea>: the above only works for U+2028 and
		1233	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1234	javascript implementations, however, have issues with other characters as
		1235	well - using C<eval> naively simply I<will> cause problems.
		1236
		1237	Another problem is that some javascript implementations reserve
		1238	some property names for their own purposes (which probably makes
		1239	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1240	C<__proto__> property name for its own purposes.
		1241
		1242	If that is a problem, you could parse try to filter the resulting JSON
		1243	output for these property strings, e.g.:
		1244
		1245	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1246
		1247	This works because C<__proto__> is not valid outside of strings, so every
		1248	occurrence of C<"__proto__"\s*:> must be a string used as property name.
		1249
		1250	If you know of other incompatibilities, please let me know.
		1251
		1252
884	=head2 JSON and YAML	1253	=head2 JSON and YAML
885		1254
886	You often hear that JSON is a subset (or a close subset) of YAML. This is,	1255	You often hear that JSON is a subset of YAML. This is, however, a mass
887	however, a mass hysteria and very far from the truth. In general, there is	1256	hysteria(*) and very far from the truth (as of the time of this writing),
888	no way to configure JSON::XS to output a data structure as valid YAML.	1257	so let me state it clearly: I<in general, there is no way to configure
		1258	JSON::XS to output a data structure as valid YAML> that works in all
		1259	cases.
889		1260
890	If you really must use JSON::XS to generate YAML, you should use this	1261	If you really must use JSON::XS to generate YAML, you should use this
891	algorithm (subject to change in future versions):	1262	algorithm (subject to change in future versions):
892		1263
893	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1264	my $to_yaml = JSON::XS->new->utf8->space_after (1);
894	my $yaml = $to_yaml->encode ($ref) . "\n";	1265	my $yaml = $to_yaml->encode ($ref) . "\n";
895		1266
896	This will usually generate JSON texts that also parse as valid	1267	This will I<usually> generate JSON texts that also parse as valid
897	YAML. Please note that YAML has hardcoded limits on (simple) object key	1268	YAML. Please note that YAML has hardcoded limits on (simple) object key
898	lengths that JSON doesn't have, so you should make sure that your hash	1269	lengths that JSON doesn't have and also has different and incompatible
		1270	unicode character escape syntax, so you should make sure that your hash
899	keys are noticeably shorter than the 1024 characters YAML allows.	1271	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1272	and that you do not have characters with codepoint values outside the
		1273	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1274	sequences in strings (which JSON::XS does not I<currently> generate, but
		1275	other JSON generators might).
900		1276
901	There might be other incompatibilities that I am not aware of. In general	1277	There might be other incompatibilities that I am not aware of (or the YAML
		1278	specification has been changed yet again - it does so quite often). In
902	you should not try to generate YAML with a JSON generator or vice versa,	1279	general you should not try to generate YAML with a JSON generator or vice
903	or try to parse JSON with a YAML parser or vice versa: chances are high	1280	versa, or try to parse JSON with a YAML parser or vice versa: chances are
904	that you will run into severe interoperability problems.	1281	high that you will run into severe interoperability problems when you
		1282	least expect it.
		1283
		1284	=over 4
		1285
		1286	=item (*)
		1287
		1288	I have been pressured multiple times by Brian Ingerson (one of the
		1289	authors of the YAML specification) to remove this paragraph, despite him
		1290	acknowledging that the actual incompatibilities exist. As I was personally
		1291	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1292	educate people about these issues, so others do not run into the same
		1293	problem again and again. After this, Brian called me a (quote)I<complete
		1294	and worthless idiot>(unquote).
		1295
		1296	In my opinion, instead of pressuring and insulting people who actually
		1297	clarify issues with YAML and the wrong statements of some of its
		1298	proponents, I would kindly suggest reading the JSON spec (which is not
		1299	that difficult or long) and finally make YAML compatible to it, and
		1300	educating users about the changes, instead of spreading lies about the
		1301	real compatibility for many I<years> and trying to silence people who
		1302	point out that it isn't true.
		1303
		1304	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1305	though the incompatibilities have been documented (and are known to Brian)
		1306	for many years and the spec makes explicit claims that YAML is a superset
		1307	of JSON. It would be so easy to fix, but apparently, bullying people and
		1308	corrupting userdata is so much easier.
		1309
		1310	=back
905		1311
906		1312
907	=head2 SPEED	1313	=head2 SPEED
908		1314
909	It seems that JSON::XS is surprisingly fast, as shown in the following	1315	It seems that JSON::XS is surprisingly fast, as shown in the following
910	tables. They have been generated with the help of the C<eg/bench> program	1316	tables. They have been generated with the help of the C<eg/bench> program
911	in the JSON::XS distribution, to make it easy to compare on your own	1317	in the JSON::XS distribution, to make it easy to compare on your own
912	system.	1318	system.
913		1319
914	First comes a comparison between various modules using a very short	1320	First comes a comparison between various modules using
915	single-line JSON string:	1321	a very short single-line JSON string (also available at
		1322	L<http://dist.schmorp.de/misc/json/short.json>).
916		1323
917	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1324	{"method": "handleMessage", "params": ["user1",
918	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1325	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1326	1, 0]}
919		1327
920	It shows the number of encodes/decodes per second (JSON::XS uses	1328	It shows the number of encodes/decodes per second (JSON::XS uses
921	the functional interface, while JSON::XS/2 uses the OO interface	1329	the functional interface, while JSON::XS/2 uses the OO interface
922	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1330	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
923	shrink). Higher is better:	1331	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1332	uses the from_json method). Higher is better:
924		1333
925	module \| encode \| decode \|	1334	module \| encode \| decode \|
926	-----------\|------------\|------------\|	1335	--------------\|------------\|------------\|
927	JSON 1.x \| 4990.842 \| 4088.813 \|	1336	JSON::DWIW/DS \| 86302.551 \| 102300.098 \|
928	JSON::DWIW \| 51653.990 \| 71575.154 \|	1337	JSON::DWIW/FJ \| 86302.551 \| 75983.768 \|
929	JSON::PC \| 65948.176 \| 74631.744 \|	1338	JSON::PP \| 15827.562 \| 6638.658 \|
930	JSON::PP \| 8931.652 \| 3817.168 \|	1339	JSON::Syck \| 63358.066 \| 47662.545 \|
931	JSON::Syck \| 24877.248 \| 27776.848 \|	1340	JSON::XS \| 511500.488 \| 511500.488 \|
932	JSON::XS \| 388361.481 \| 227951.304 \|	1341	JSON::XS/2 \| 291271.111 \| 388361.481 \|
933	JSON::XS/2 \| 227951.304 \| 218453.333 \|	1342	JSON::XS/3 \| 361577.931 \| 361577.931 \|
934	JSON::XS/3 \| 338250.323 \| 218453.333 \|	1343	Storable \| 66788.280 \| 265462.278 \|
935	Storable \| 16500.016 \| 135300.129 \|
936	-----------+------------+------------+	1344	--------------+------------+------------+
937		1345
938	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,	1346	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
939	about three times faster on decoding, and over forty times faster	1347	about five times faster on decoding, and over thirty to seventy times
940	than JSON, even with pretty-printing and key sorting. It also compares	1348	faster than JSON's pure perl implementation. It also compares favourably
941	favourably to Storable for small amounts of data.	1349	to Storable for small amounts of data.
942		1350
943	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1351	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
944	search API (http://nanoref.com/yahooapis/mgPdGg):	1352	search API (L<http://dist.schmorp.de/misc/json/long.json>).
945		1353
946	module \| encode \| decode \|	1354	module \| encode \| decode \|
947	-----------\|------------\|------------\|	1355	--------------\|------------\|------------\|
948	JSON 1.x \| 55.260 \| 34.971 \|	1356	JSON::DWIW/DS \| 1647.927 \| 2673.916 \|
949	JSON::DWIW \| 825.228 \| 1082.513 \|	1357	JSON::DWIW/FJ \| 1630.249 \| 2596.128 \|
950	JSON::PC \| 3571.444 \| 2394.829 \|
951	JSON::PP \| 210.987 \| 32.574 \|	1358	JSON::PP \| 400.640 \| 62.311 \|
952	JSON::Syck \| 552.551 \| 787.544 \|	1359	JSON::Syck \| 1481.040 \| 1524.869 \|
953	JSON::XS \| 5780.463 \| 4854.519 \|	1360	JSON::XS \| 20661.596 \| 9541.183 \|
954	JSON::XS/2 \| 3869.998 \| 4798.975 \|	1361	JSON::XS/2 \| 10683.403 \| 9416.938 \|
955	JSON::XS/3 \| 5862.880 \| 4798.975 \|	1362	JSON::XS/3 \| 20661.596 \| 9400.054 \|
956	Storable \| 4445.002 \| 5235.027 \|	1363	Storable \| 19765.806 \| 10000.725 \|
957	-----------+------------+------------+	1364	--------------+------------+------------+
958		1365
959	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1366	Again, JSON::XS leads by far (except for Storable which non-surprisingly
960	decodes faster).	1367	decodes a bit faster).
961		1368
962	On large strings containing lots of high Unicode characters, some modules	1369	On large strings containing lots of high Unicode characters, some modules
963	(such as JSON::PC) seem to decode faster than JSON::XS, but the result	1370	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
964	will be broken due to missing (or wrong) Unicode handling. Others refuse	1371	will be broken due to missing (or wrong) Unicode handling. Others refuse
965	to decode or encode properly, so it was impossible to prepare a fair	1372	to decode or encode properly, so it was impossible to prepare a fair
…		…
986		1393
987	Third, JSON::XS recurses using the C stack when decoding objects and	1394	Third, JSON::XS recurses using the C stack when decoding objects and
988	arrays. The C stack is a limited resource: for instance, on my amd64	1395	arrays. The C stack is a limited resource: for instance, on my amd64
989	machine with 8MB of stack size I can decode around 180k nested arrays but	1396	machine with 8MB of stack size I can decode around 180k nested arrays but
990	only 14k nested JSON objects (due to perl itself recursing deeply on croak	1397	only 14k nested JSON objects (due to perl itself recursing deeply on croak
991	to free the temporary). If that is exceeded, the program crashes. to be	1398	to free the temporary). If that is exceeded, the program crashes. To be
992	conservative, the default nesting limit is set to 512. If your process	1399	conservative, the default nesting limit is set to 512. If your process
993	has a smaller stack, you should adjust this setting accordingly with the	1400	has a smaller stack, you should adjust this setting accordingly with the
994	C<max_depth> method.	1401	C<max_depth> method.
995		1402
996	And last but least, something else could bomb you that I forgot to think	1403	Something else could bomb you, too, that I forgot to think of. In that
997	of. In that case, you get to keep the pieces. I am always open for hints,	1404	case, you get to keep the pieces. I am always open for hints, though...
998	though...	1405
		1406	Also keep in mind that JSON::XS might leak contents of your Perl data
		1407	structures in its error messages, so when you serialise sensitive
		1408	information you might want to make sure that exceptions thrown by JSON::XS
		1409	will not end up in front of untrusted eyes.
999		1410
1000	If you are using JSON::XS to return packets to consumption	1411	If you are using JSON::XS to return packets to consumption
1001	by JavaScript scripts in a browser you should have a look at	1412	by JavaScript scripts in a browser you should have a look at
1002	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether	1413	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
1003	you are vulnerable to some common attack vectors (which really are browser	1414	see whether you are vulnerable to some common attack vectors (which really
1004	design bugs, but it is still you who will have to deal with it, as major	1415	are browser design bugs, but it is still you who will have to deal with
1005	browser developers care only for features, not about doing security	1416	it, as major browser developers care only for features, not about getting
1006	right).	1417	security right).
1007		1418
1008		1419
1009	=head1 THREADS	1420	=head1 THREADS
1010		1421
1011	This module is I<not> guaranteed to be thread safe and there are no	1422	This module is I<not> guaranteed to be thread safe and there are no
1012	plans to change this until Perl gets thread support (as opposed to the	1423	plans to change this until Perl gets thread support (as opposed to the
1013	horribly slow so-called "threads" which are simply slow and bloated	1424	horribly slow so-called "threads" which are simply slow and bloated
1014	process simulations - use fork, its I<much> faster, cheaper, better).	1425	process simulations - use fork, it's I<much> faster, cheaper, better).
1015		1426
1016	(It might actually work, but you have been warned).	1427	(It might actually work, but you have been warned).
1017		1428
1018		1429
		1430	=head1 THE PERILS OF SETLOCALE
		1431
		1432	Sometimes people avoid the Perl locale support and directly call the
		1433	system's setlocale function with C<LC_ALL>.
		1434
		1435	This breaks both perl and modules such as JSON::XS, as stringification of
		1436	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1437	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1438	perl to stringify numbers).
		1439
		1440	The solution is simple: don't call C<setlocale>, or use it for only those
		1441	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1442
		1443	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1444	actually needs it (avoiding stringification of numbers), and restore it
		1445	afterwards.
		1446
		1447
1019	=head1 BUGS	1448	=head1 BUGS
1020		1449
1021	While the goal of this module is to be correct, that unfortunately does	1450	While the goal of this module is to be correct, that unfortunately does
1022	not mean its bug-free, only that I think its design is bug-free. It is	1451	not mean it's bug-free, only that I think its design is bug-free. If you
1023	still relatively early in its development. If you keep reporting bugs they	1452	keep reporting bugs they will be fixed swiftly, though.
1024	will be fixed swiftly, though.
1025		1453
1026	Please refrain from using rt.cpan.org or any other bug reporting	1454	Please refrain from using rt.cpan.org or any other bug reporting
1027	service. I put the contact address into my modules for a reason.	1455	service. I put the contact address into my modules for a reason.
1028		1456
1029	=cut	1457	=cut
…		…
1049	"--" => sub { $_[0] = ${$_[0]} - 1 },	1477	"--" => sub { $_[0] = ${$_[0]} - 1 },
1050	fallback => 1;	1478	fallback => 1;
1051		1479
1052	1;	1480	1;
1053		1481
		1482	=head1 SEE ALSO
		1483
		1484	The F<json_xs> command line utility for quick experiments.
		1485
1054	=head1 AUTHOR	1486	=head1 AUTHOR
1055		1487
1056	Marc Lehmann <schmorp@schmorp.de>	1488	Marc Lehmann <schmorp@schmorp.de>
1057	http://home.schmorp.de/	1489	http://home.schmorp.de/
1058		1490

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Revision 1.72 by root, Sun Nov 25 19:11:07 2007 UTC vs.
Revision 1.143 by root, Fri Oct 25 20:02:54 2013 UTC