[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 1.121 by root, Mon Jul 13 22:13:17 2009 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, the deserialised data structure is identical on the Perl level.
54	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks	70	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
55	like a number).	71	like a number). There minor I<are> exceptions to this, read the MAPPING
		72	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 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 $VERSION = '2.24';
90	our @ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
91		108
92	our @EXPORT = qw(to_json from_json);	109	our @EXPORT = qw(encode_json decode_json to_json from_json);
		110
		111	sub to_json($) {
		112	require Carp;
		113	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
		114	}
		115
		116	sub from_json($) {
		117	require Carp;
		118	Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
		119	}
93		120
94	use Exporter;	121	use Exporter;
95	use XSLoader;	122	use XSLoader;
96		123
97	=head1 FUNCTIONAL INTERFACE	124	=head1 FUNCTIONAL INTERFACE
…		…
99	The following convenience methods are provided by this module. They are	126	The following convenience methods are provided by this module. They are
100	exported by default:	127	exported by default:
101		128
102	=over 4	129	=over 4
103		130
104	=item $json_text = to_json $perl_scalar	131	=item $json_text = encode_json $perl_scalar
105		132
106	Converts the given Perl data structure to a UTF-8 encoded, binary string	133	Converts the given Perl data structure to a UTF-8 encoded, binary string
107	(that is, the string contains octets only). Croaks on error.	134	(that is, the string contains octets only). Croaks on error.
108		135
109	This function call is functionally identical to:	136	This function call is functionally identical to:
110		137
111	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	138	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
112		139
113	except being faster.	140	Except being faster.
114		141
115	=item $perl_scalar = from_json $json_text	142	=item $perl_scalar = decode_json $json_text
116		143
117	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries	144	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	145	to parse that as an UTF-8 encoded JSON text, returning the resulting
119	reference. Croaks on error.	146	reference. Croaks on error.
120		147
121	This function call is functionally identical to:	148	This function call is functionally identical to:
122		149
123	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	150	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
124		151
125	except being faster.	152	Except being faster.
126		153
127	=item $is_boolean = JSON::XS::is_bool $scalar	154	=item $is_boolean = JSON::XS::is_bool $scalar
128		155
129	Returns true if the passed scalar represents either JSON::XS::true or	156	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	157	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	175	This enables you to store Unicode characters as single characters in a
149	Perl string - very natural.	176	Perl string - very natural.
150		177
151	=item 2. Perl does I<not> associate an encoding with your strings.	178	=item 2. Perl does I<not> associate an encoding with your strings.
152		179
153	Unless you force it to, e.g. when matching it against a regex, or printing	180	... 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	181	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	182	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	183	on various settings. In no case is an encoding stored together with your
157	I<use> that decides encoding, not any magical metadata.	184	data, it is I<use> that decides encoding, not any magical meta data.
158		185
159	=item 3. The internal utf-8 flag has no meaning with regards to the	186	=item 3. The internal utf-8 flag has no meaning with regards to the
160	encoding of your string.	187	encoding of your string.
161		188
162	Just ignore that flag unless you debug a Perl bug, a module written in	189	Just ignore that flag unless you debug a Perl bug, a module written in
…		…
168		195
169	If you didn't know about that flag, just the better, pretend it doesn't	196	If you didn't know about that flag, just the better, pretend it doesn't
170	exist.	197	exist.
171		198
172	=item 4. A "Unicode String" is simply a string where each character can be	199	=item 4. A "Unicode String" is simply a string where each character can be
173	validly interpreted as a Unicode codepoint.	200	validly interpreted as a Unicode code point.
174		201
175	If you have UTF-8 encoded data, it is no longer a Unicode string, but a	202	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.	203	Unicode string encoded in UTF-8, giving you a binary string.
177		204
178	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.	205	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
…		…
216		243
217	If C<$enable> is false, then the C<encode> method will not escape Unicode	244	If C<$enable> is false, then the C<encode> method will not escape Unicode
218	characters unless required by the JSON syntax or other flags. This results	245	characters unless required by the JSON syntax or other flags. This results
219	in a faster and more compact format.	246	in a faster and more compact format.
220		247
		248	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		249	document.
		250
221	The main use for this flag is to produce JSON texts that can be	251	The main use for this flag is to produce JSON texts that can be
222	transmitted over a 7-bit channel, as the encoded JSON texts will not	252	transmitted over a 7-bit channel, as the encoded JSON texts will not
223	contain any 8 bit characters.	253	contain any 8 bit characters.
224		254
225	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	255	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
…		…
236	will not be affected in any way by this flag, as C<decode> by default	266	will not be affected in any way by this flag, as C<decode> by default
237	expects Unicode, which is a strict superset of latin1.	267	expects Unicode, which is a strict superset of latin1.
238		268
239	If C<$enable> is false, then the C<encode> method will not escape Unicode	269	If C<$enable> is false, then the C<encode> method will not escape Unicode
240	characters unless required by the JSON syntax or other flags.	270	characters unless required by the JSON syntax or other flags.
		271
		272	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		273	document.
241		274
242	The main use for this flag is efficiently encoding binary data as JSON	275	The main use for this flag is efficiently encoding binary data as JSON
243	text, as most octets will not be escaped, resulting in a smaller encoded	276	text, as most octets will not be escaped, resulting in a smaller encoded
244	size. The disadvantage is that the resulting JSON text is encoded	277	size. The disadvantage is that the resulting JSON text is encoded
245	in latin1 (and must correctly be treated as such when storing and	278	in latin1 (and must correctly be treated as such when storing and
…		…
265	If C<$enable> is false, then the C<encode> method will return the JSON	298	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	299	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	300	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.	301	to be done yourself, e.g. using the Encode module.
269		302
		303	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		304	document.
		305
270	Example, output UTF-16BE-encoded JSON:	306	Example, output UTF-16BE-encoded JSON:
271		307
272	use Encode;	308	use Encode;
273	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	309	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
274		310
…		…
276		312
277	use Encode;	313	use Encode;
278	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);	314	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
279		315
280	=item $json = $json->pretty ([$enable])	316	=item $json = $json->pretty ([$enable])
281
282	=item $enabled = $json->get_pretty
283		317
284	This enables (or disables) all of the C<indent>, C<space_before> and	318	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	319	C<space_after> (and in the future possibly more) flags in one call to
286	generate the most readable (or most compact) form possible.	320	generate the most readable (or most compact) form possible.
287		321
…		…
427	resulting in an invalid JSON text:	461	resulting in an invalid JSON text:
428		462
429	JSON::XS->new->allow_nonref->encode ("Hello, World!")	463	JSON::XS->new->allow_nonref->encode ("Hello, World!")
430	=> "Hello, World!"	464	=> "Hello, World!"
431		465
		466	=item $json = $json->allow_unknown ([$enable])
		467
		468	=item $enabled = $json->get_allow_unknown
		469
		470	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		471	exception when it encounters values it cannot represent in JSON (for
		472	example, filehandles) but instead will encode a JSON C<null> value. Note
		473	that blessed objects are not included here and are handled separately by
		474	c<allow_nonref>.
		475
		476	If C<$enable> is false (the default), then C<encode> will throw an
		477	exception when it encounters anything it cannot encode as JSON.
		478
		479	This option does not affect C<decode> in any way, and it is recommended to
		480	leave it off unless you know your communications partner.
		481
432	=item $json = $json->allow_blessed ([$enable])	482	=item $json = $json->allow_blessed ([$enable])
433		483
434	=item $enabled = $json->get_allow_bless	484	=item $enabled = $json->get_allow_blessed
435		485
436	If C<$enable> is true (or missing), then the C<encode> method will not	486	If C<$enable> is true (or missing), then the C<encode> method will not
437	barf when it encounters a blessed reference. Instead, the value of the	487	barf when it encounters a blessed reference. Instead, the value of the
438	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>	488	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
439	disabled or no C<to_json> method found) or a representation of the	489	disabled or no C<TO_JSON> method found) or a representation of the
440	object (C<convert_blessed> enabled and C<to_json> method found) is being	490	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
441	encoded. Has no effect on C<decode>.	491	encoded. Has no effect on C<decode>.
442		492
443	If C<$enable> is false (the default), then C<encode> will throw an	493	If C<$enable> is false (the default), then C<encode> will throw an
444	exception when it encounters a blessed object.	494	exception when it encounters a blessed object.
445		495
…		…
457	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>	507	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	508	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	509	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	510	(== 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	511	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>	512	usually in upper case letters and to avoid collisions with any C<to_json>
463	function.	513	function or method.
464		514
465	This setting does not yet influence C<decode> in any way, but in the	515	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	516	future, global hooks might get installed that influence C<decode> and are
467	enabled by this setting.	517	enabled by this setting.
468		518
…		…
576	=item $json = $json->max_depth ([$maximum_nesting_depth])	626	=item $json = $json->max_depth ([$maximum_nesting_depth])
577		627
578	=item $max_depth = $json->get_max_depth	628	=item $max_depth = $json->get_max_depth
579		629
580	Sets the maximum nesting level (default C<512>) accepted while encoding	630	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	631	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	632	data structure, then the encoder and decoder will stop and croak at that
583	stop and croak at that point.	633	point.
584		634
585	Nesting level is defined by number of hash- or arrayrefs that the encoder	635	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<[>	636	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	637	characters without their matching closing parenthesis crossed to reach a
588	given character in a string.	638	given character in a string.
589		639
590	Setting the maximum depth to one disallows any nesting, so that ensures	640	Setting the maximum depth to one disallows any nesting, so that ensures
591	that the object is only a single hash/object or array.	641	that the object is only a single hash/object or array.
592		642
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	643	If no argument is given, the highest possible setting will be used, which
595	used, which is rarely useful.	644	is rarely useful.
		645
		646	Note that nesting is implemented by recursion in C. The default value has
		647	been chosen to be as large as typical operating systems allow without
		648	crashing.
596		649
597	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	650	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
598		651
599	=item $json = $json->max_size ([$maximum_string_size])	652	=item $json = $json->max_size ([$maximum_string_size])
600		653
601	=item $max_size = $json->get_max_size	654	=item $max_size = $json->get_max_size
602		655
603	Set the maximum length a JSON text may have (in bytes) where decoding is	656	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>	657	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	658	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	659	attempt to decode the string but throw an exception. This setting has no
607	effect on C<encode> (yet).	660	effect on C<encode> (yet).
608		661
609	The argument to C<max_size> will be rounded up to the next B<highest>	662	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	663	C<0> is specified).
611	limit check will be deactivated (same as when C<0> is specified).
612		664
613	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	665	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
614		666
615	=item $json_text = $json->encode ($perl_scalar)	667	=item $json_text = $json->encode ($perl_scalar)
616		668
…		…
645	=> ([], 3)	697	=> ([], 3)
646		698
647	=back	699	=back
648		700
649		701
		702	=head1 INCREMENTAL PARSING
		703
		704	In some cases, there is the need for incremental parsing of JSON
		705	texts. While this module always has to keep both JSON text and resulting
		706	Perl data structure in memory at one time, it does allow you to parse a
		707	JSON stream incrementally. It does so by accumulating text until it has
		708	a full JSON object, which it then can decode. This process is similar to
		709	using C<decode_prefix> to see if a full JSON object is available, but
		710	is much more efficient (and can be implemented with a minimum of method
		711	calls).
		712
		713	JSON::XS will only attempt to parse the JSON text once it is sure it
		714	has enough text to get a decisive result, using a very simple but
		715	truly incremental parser. This means that it sometimes won't stop as
		716	early as the full parser, for example, it doesn't detect parenthese
		717	mismatches. The only thing it guarantees is that it starts decoding as
		718	soon as a syntactically valid JSON text has been seen. This means you need
		719	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		720	parsing in the presence if syntax errors.
		721
		722	The following methods implement this incremental parser.
		723
		724	=over 4
		725
		726	=item [void, scalar or list context] = $json->incr_parse ([$string])
		727
		728	This is the central parsing function. It can both append new text and
		729	extract objects from the stream accumulated so far (both of these
		730	functions are optional).
		731
		732	If C<$string> is given, then this string is appended to the already
		733	existing JSON fragment stored in the C<$json> object.
		734
		735	After that, if the function is called in void context, it will simply
		736	return without doing anything further. This can be used to add more text
		737	in as many chunks as you want.
		738
		739	If the method is called in scalar context, then it will try to extract
		740	exactly I<one> JSON object. If that is successful, it will return this
		741	object, otherwise it will return C<undef>. If there is a parse error,
		742	this method will croak just as C<decode> would do (one can then use
		743	C<incr_skip> to skip the errornous part). This is the most common way of
		744	using the method.
		745
		746	And finally, in list context, it will try to extract as many objects
		747	from the stream as it can find and return them, or the empty list
		748	otherwise. For this to work, there must be no separators between the JSON
		749	objects or arrays, instead they must be concatenated back-to-back. If
		750	an error occurs, an exception will be raised as in the scalar context
		751	case. Note that in this case, any previously-parsed JSON texts will be
		752	lost.
		753
		754	=item $lvalue_string = $json->incr_text
		755
		756	This method returns the currently stored JSON fragment as an lvalue, that
		757	is, you can manipulate it. This I<only> works when a preceding call to
		758	C<incr_parse> in I<scalar context> successfully returned an object. Under
		759	all other circumstances you must not call this function (I mean it.
		760	although in simple tests it might actually work, it I<will> fail under
		761	real world conditions). As a special exception, you can also call this
		762	method before having parsed anything.
		763
		764	This function is useful in two cases: a) finding the trailing text after a
		765	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		766	(such as commas).
		767
		768	=item $json->incr_skip
		769
		770	This will reset the state of the incremental parser and will remove
		771	the parsed text from the input buffer so far. This is useful after
		772	C<incr_parse> died, in which case the input buffer and incremental parser
		773	state is left unchanged, to skip the text parsed so far and to reset the
		774	parse state.
		775
		776	The difference to C<incr_reset> is that only text until the parse error
		777	occured is removed.
		778
		779	=item $json->incr_reset
		780
		781	This completely resets the incremental parser, that is, after this call,
		782	it will be as if the parser had never parsed anything.
		783
		784	This is useful if you want to repeatedly parse JSON objects and want to
		785	ignore any trailing data, which means you have to reset the parser after
		786	each successful decode.
		787
		788	=back
		789
		790	=head2 LIMITATIONS
		791
		792	All options that affect decoding are supported, except
		793	C<allow_nonref>. The reason for this is that it cannot be made to
		794	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		795	them back to back and still decode them perfectly. This does not hold true
		796	for JSON numbers, however.
		797
		798	For example, is the string C<1> a single JSON number, or is it simply the
		799	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		800	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		801	takes the conservative route and disallows this case.
		802
		803	=head2 EXAMPLES
		804
		805	Some examples will make all this clearer. First, a simple example that
		806	works similarly to C<decode_prefix>: We want to decode the JSON object at
		807	the start of a string and identify the portion after the JSON object:
		808
		809	my $text = "[1,2,3] hello";
		810
		811	my $json = new JSON::XS;
		812
		813	my $obj = $json->incr_parse ($text)
		814	or die "expected JSON object or array at beginning of string";
		815
		816	my $tail = $json->incr_text;
		817	# $tail now contains " hello"
		818
		819	Easy, isn't it?
		820
		821	Now for a more complicated example: Imagine a hypothetical protocol where
		822	you read some requests from a TCP stream, and each request is a JSON
		823	array, without any separation between them (in fact, it is often useful to
		824	use newlines as "separators", as these get interpreted as whitespace at
		825	the start of the JSON text, which makes it possible to test said protocol
		826	with C<telnet>...).
		827
		828	Here is how you'd do it (it is trivial to write this in an event-based
		829	manner):
		830
		831	my $json = new JSON::XS;
		832
		833	# read some data from the socket
		834	while (sysread $socket, my $buf, 4096) {
		835
		836	# split and decode as many requests as possible
		837	for my $request ($json->incr_parse ($buf)) {
		838	# act on the $request
		839	}
		840	}
		841
		842	Another complicated example: Assume you have a string with JSON objects
		843	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		844	[3]>). To parse them, we have to skip the commas between the JSON texts,
		845	and here is where the lvalue-ness of C<incr_text> comes in useful:
		846
		847	my $text = "[1],[2], [3]";
		848	my $json = new JSON::XS;
		849
		850	# void context, so no parsing done
		851	$json->incr_parse ($text);
		852
		853	# now extract as many objects as possible. note the
		854	# use of scalar context so incr_text can be called.
		855	while (my $obj = $json->incr_parse) {
		856	# do something with $obj
		857
		858	# now skip the optional comma
		859	$json->incr_text =~ s/^ \s* , //x;
		860	}
		861
		862	Now lets go for a very complex example: Assume that you have a gigantic
		863	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		864	but you cannot load it into memory fully (this has actually happened in
		865	the real world :).
		866
		867	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		868	can still help you: You implement a (very simple) array parser and let
		869	JSON decode the array elements, which are all full JSON objects on their
		870	own (this wouldn't work if the array elements could be JSON numbers, for
		871	example):
		872
		873	my $json = new JSON::XS;
		874
		875	# open the monster
		876	open my $fh, "<bigfile.json"
		877	or die "bigfile: $!";
		878
		879	# first parse the initial "["
		880	for (;;) {
		881	sysread $fh, my $buf, 65536
		882	or die "read error: $!";
		883	$json->incr_parse ($buf); # void context, so no parsing
		884
		885	# Exit the loop once we found and removed(!) the initial "[".
		886	# In essence, we are (ab-)using the $json object as a simple scalar
		887	# we append data to.
		888	last if $json->incr_text =~ s/^ \s* \[ //x;
		889	}
		890
		891	# now we have the skipped the initial "[", so continue
		892	# parsing all the elements.
		893	for (;;) {
		894	# in this loop we read data until we got a single JSON object
		895	for (;;) {
		896	if (my $obj = $json->incr_parse) {
		897	# do something with $obj
		898	last;
		899	}
		900
		901	# add more data
		902	sysread $fh, my $buf, 65536
		903	or die "read error: $!";
		904	$json->incr_parse ($buf); # void context, so no parsing
		905	}
		906
		907	# in this loop we read data until we either found and parsed the
		908	# separating "," between elements, or the final "]"
		909	for (;;) {
		910	# first skip whitespace
		911	$json->incr_text =~ s/^\s*//;
		912
		913	# if we find "]", we are done
		914	if ($json->incr_text =~ s/^\]//) {
		915	print "finished.\n";
		916	exit;
		917	}
		918
		919	# if we find ",", we can continue with the next element
		920	if ($json->incr_text =~ s/^,//) {
		921	last;
		922	}
		923
		924	# if we find anything else, we have a parse error!
		925	if (length $json->incr_text) {
		926	die "parse error near ", $json->incr_text;
		927	}
		928
		929	# else add more data
		930	sysread $fh, my $buf, 65536
		931	or die "read error: $!";
		932	$json->incr_parse ($buf); # void context, so no parsing
		933	}
		934
		935	This is a complex example, but most of the complexity comes from the fact
		936	that we are trying to be correct (bear with me if I am wrong, I never ran
		937	the above example :).
		938
		939
		940
650	=head1 MAPPING	941	=head1 MAPPING
651		942
652	This section describes how JSON::XS maps Perl values to JSON values and	943	This section describes how JSON::XS maps Perl values to JSON values and
653	vice versa. These mappings are designed to "do the right thing" in most	944	vice versa. These mappings are designed to "do the right thing" in most
654	circumstances automatically, preserving round-tripping characteristics	945	circumstances automatically, preserving round-tripping characteristics
…		…
682		973
683	A JSON number becomes either an integer, numeric (floating point) or	974	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	975	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	976	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	977	the conversion details, but an integer may take slightly less memory and
687	might represent more values exactly than (floating point) numbers.	978	might represent more values exactly than floating point numbers.
688		979
689	If the number consists of digits only, JSON::XS will try to represent	980	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	981	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	982	a numeric (floating point) value if that is possible without loss of
692	precision. Otherwise it will preserve the number as a string value.	983	precision. Otherwise it will preserve the number as a string value (in
		984	which case you lose roundtripping ability, as the JSON number will be
		985	re-encoded toa JSON string).
693		986
694	Numbers containing a fractional or exponential part will always be	987	Numbers containing a fractional or exponential part will always be
695	represented as numeric (floating point) values, possibly at a loss of	988	represented as numeric (floating point) values, possibly at a loss of
696	precision.	989	precision (in which case you might lose perfect roundtripping ability, but
697		990	the JSON number will still be re-encoded as a JSON number).
698	This might create round-tripping problems as numbers might become strings,
699	but as Perl is typeless there is no other way to do it.
700		991
701	=item true, false	992	=item true, false
702		993
703	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	994	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	995	respectively. They are overloaded to act almost exactly like the numbers
…		…
741	Other unblessed references are generally not allowed and will cause an	1032	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	1033	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	1034	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.	1035	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
745		1036
746	to_json [\0,JSON::XS::true] # yields [false,true]	1037	encode_json [\0, JSON::XS::true] # yields [false,true]
747		1038
748	=item JSON::XS::true, JSON::XS::false	1039	=item JSON::XS::true, JSON::XS::false
749		1040
750	These special values become JSON true and JSON false values,	1041	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.	1042	respectively. You can also use C<\1> and C<\0> directly if you want.
752		1043
753	=item blessed objects	1044	=item blessed objects
754		1045
755	Blessed objects are not allowed. JSON::XS currently tries to encode their	1046	Blessed objects are not directly representable in JSON. See the
756	underlying representation (hash- or arrayref), but this behaviour might	1047	C<allow_blessed> and C<convert_blessed> methods on various options on
757	change in future versions.	1048	how to deal with this: basically, you can choose between throwing an
		1049	exception, encoding the reference as if it weren't blessed, or provide
		1050	your own serialiser method.
758		1051
759	=item simple scalars	1052	=item simple scalars
760		1053
761	Simple Perl scalars (any scalar that is not a reference) are the most	1054	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	1055	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	1056	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:	1057	before encoding as JSON strings, and anything else as number value:
765		1058
766	# dump as number	1059	# dump as number
767	to_json [2] # yields [2]	1060	encode_json [2] # yields [2]
768	to_json [-3.0e17] # yields [-3e+17]	1061	encode_json [-3.0e17] # yields [-3e+17]
769	my $value = 5; to_json [$value] # yields [5]	1062	my $value = 5; encode_json [$value] # yields [5]
770		1063
771	# used as string, so dump as string	1064	# used as string, so dump as string
772	print $value;	1065	print $value;
773	to_json [$value] # yields ["5"]	1066	encode_json [$value] # yields ["5"]
774		1067
775	# undef becomes null	1068	# undef becomes null
776	to_json [undef] # yields [null]	1069	encode_json [undef] # yields [null]
777		1070
778	You can force the type to be a JSON string by stringifying it:	1071	You can force the type to be a JSON string by stringifying it:
779		1072
780	my $x = 3.1; # some variable containing a number	1073	my $x = 3.1; # some variable containing a number
781	"$x"; # stringified	1074	"$x"; # stringified
…		…
787	my $x = "3"; # some variable containing a string	1080	my $x = "3"; # some variable containing a string
788	$x += 0; # numify it, ensuring it will be dumped as a number	1081	$x += 0; # numify it, ensuring it will be dumped as a number
789	$x *= 1; # same thing, the choice is yours.	1082	$x *= 1; # same thing, the choice is yours.
790		1083
791	You can not currently force the type in other, less obscure, ways. Tell me	1084	You can not currently force the type in other, less obscure, ways. Tell me
792	if you need this capability.	1085	if you need this capability (but don't forget to explain why it's needed
		1086	:).
793		1087
794	=back	1088	=back
795		1089
796		1090
797	=head1 COMPARISON	1091	=head1 ENCODING/CODESET FLAG NOTES
798		1092
799	As already mentioned, this module was created because none of the existing	1093	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	1094	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,	1095	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	1096
803	from any of these problems or limitations.	1097	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1098	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1099	control whether C<encode> escapes character values outside their respective
		1100	codeset range. Neither of these flags conflict with each other, although
		1101	some combinations make less sense than others.
		1102
		1103	Care has been taken to make all flags symmetrical with respect to
		1104	C<encode> and C<decode>, that is, texts encoded with any combination of
		1105	these flag values will be correctly decoded when the same flags are used
		1106	- in general, if you use different flag settings while encoding vs. when
		1107	decoding you likely have a bug somewhere.
		1108
		1109	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1110	simply an abstract set of character-codepoint pairs, while an encoding
		1111	takes those codepoint numbers and I<encodes> them, in our case into
		1112	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1113	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1114	the same time, which can be confusing.
804		1115
805	=over 4	1116	=over 4
806		1117
807	=item JSON 1.07	1118	=item C<utf8> flag disabled
808		1119
809	Slow (but very portable, as it is written in pure Perl).	1120	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1121	and expect Unicode strings, that is, characters with high ordinal Unicode
		1122	values (> 255) will be encoded as such characters, and likewise such
		1123	characters are decoded as-is, no canges to them will be done, except
		1124	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1125	respectively (to Perl, these are the same thing in strings unless you do
		1126	funny/weird/dumb stuff).
810		1127
811	Undocumented/buggy Unicode handling (how JSON handles Unicode values is	1128	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	1129	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).	1130	the encoding for you (for example, when printing to a terminal using a
		1131	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1132	to UTF-8 encode your data first and have Perl encode it another time).
814		1133
815	No round-tripping (strings get clobbered if they look like numbers, e.g.	1134	=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		1135
819	=item JSON::PC 0.01	1136	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1137	characters using the corresponding UTF-8 multi-byte sequence, and will
		1138	expect your input strings to be encoded as UTF-8, that is, no "character"
		1139	of the input string must have any value > 255, as UTF-8 does not allow
		1140	that.
820		1141
821	Very fast.	1142	The C<utf8> flag therefore switches between two modes: disabled means you
		1143	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1144	octet/binary string in Perl.
822		1145
823	Undocumented/buggy Unicode handling.	1146	=item C<latin1> or C<ascii> flags enabled
824		1147
825	No round-tripping.	1148	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1149	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1150	characters as specified by the C<utf8> flag.
826		1151
827	Has problems handling many Perl values (e.g. regex results and other magic	1152	If C<utf8> is disabled, then the result is also correctly encoded in those
828	values will make it croak).	1153	character sets (as both are proper subsets of Unicode, meaning that a
		1154	Unicode string with all character values < 256 is the same thing as a
		1155	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1156	the same thing as an ASCII string in Perl).
829		1157
830	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1158	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
831	which is not a valid JSON text.	1159	regardless of these flags, just some more characters will be escaped using
		1160	C<\uXXXX> then before.
832		1161
833	Unmaintained (maintainer unresponsive for many months, bugs are not	1162	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
834	getting fixed).	1163	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1164	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1165	a subset of Unicode), while ASCII is.
835		1166
836	=item JSON::Syck 0.21	1167	Surprisingly, C<decode> will ignore these flags and so treat all input
		1168	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1169	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1170	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
837		1171
838	Very buggy (often crashes).	1172	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1173	they only govern when the JSON output engine escapes a character or not.
839		1174
840	Very inflexible (no human-readable format supported, format pretty much	1175	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	1176	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		1177
845	Completely broken (and confusingly documented) Unicode handling (Unicode	1178	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	1179	with values > 127, which means you can interpret the resulting string
847	I<different> values on en- and decoding to get symmetric behaviour).	1180	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
848		1181	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	1182	when your channel for JSON transfer is not 8-bit clean or the encoding
850	value was used in a numeric context or not).	1183	might be mangled in between (e.g. in mail), and works because ASCII is a
851		1184	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		1185
881	=back	1186	=back
882		1187
883		1188
		1189	=head2 JSON and ECMAscript
		1190
		1191	JSON syntax is based on how literals are represented in javascript (the
		1192	not-standardised predecessor of ECMAscript) which is presumably why it is
		1193	called "JavaScript Object Notation".
		1194
		1195	However, JSON is not a subset (and also not a superset of course) of
		1196	ECMAscript (the standard) or javascript (whatever browsers actually
		1197	implement).
		1198
		1199	If you want to use javascript's C<eval> function to "parse" JSON, you
		1200	might run into parse errors for valid JSON texts, or the resulting data
		1201	structure might not be queryable:
		1202
		1203	One of the problems is that U+2028 and U+2029 are valid characters inside
		1204	JSON strings, but are not allowed in ECMAscript string literals, so the
		1205	following Perl fragment will not output something that can be guaranteed
		1206	to be parsable by javascript's C<eval>:
		1207
		1208	use JSON::XS;
		1209
		1210	print encode_json [chr 0x2028];
		1211
		1212	The right fix for this is to use a proper JSON parser in your javascript
		1213	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1214	F<json2.js> parser).
		1215
		1216	If this is not an option, you can, as a stop-gap measure, simply encode to
		1217	ASCII-only JSON:
		1218
		1219	use JSON::XS;
		1220
		1221	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1222
		1223	Note that this will enlarge the resulting JSON text quite a bit if you
		1224	have many non-ASCII characters. You might be tempted to run some regexes
		1225	to only escape U+2028 and U+2029, e.g.:
		1226
		1227	# DO NOT USE THIS!
		1228	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1229	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1230	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1231	print $json;
		1232
		1233	Note that I<this is a bad idea>: the above only works for U+2028 and
		1234	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1235	javascript implementations, however, have issues with other characters as
		1236	well - using C<eval> naively simply I<will> cause problems.
		1237
		1238	Another problem is that some javascript implementations reserve
		1239	some property names for their own purposes (which probably makes
		1240	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1241	C<__proto__> property name for it's own purposes.
		1242
		1243	If that is a problem, you could parse try to filter the resulting JSON
		1244	output for these property strings, e.g.:
		1245
		1246	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1247
		1248	This works because C<__proto__> is not valid outside of strings, so every
		1249	occurence of C<"__proto__"\s*:> must be a string used as property name.
		1250
		1251	If you know of other incompatibilities, please let me know.
		1252
		1253
884	=head2 JSON and YAML	1254	=head2 JSON and YAML
885		1255
886	You often hear that JSON is a subset (or a close subset) of YAML. This is,	1256	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	1257	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.	1258	so let me state it clearly: I<in general, there is no way to configure
		1259	JSON::XS to output a data structure as valid YAML> that works in all
		1260	cases.
889		1261
890	If you really must use JSON::XS to generate YAML, you should use this	1262	If you really must use JSON::XS to generate YAML, you should use this
891	algorithm (subject to change in future versions):	1263	algorithm (subject to change in future versions):
892		1264
893	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1265	my $to_yaml = JSON::XS->new->utf8->space_after (1);
894	my $yaml = $to_yaml->encode ($ref) . "\n";	1266	my $yaml = $to_yaml->encode ($ref) . "\n";
895		1267
896	This will usually generate JSON texts that also parse as valid	1268	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	1269	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	1270	lengths that JSON doesn't have and also has different and incompatible
		1271	unicode handling, so you should make sure that your hash keys are
899	keys are noticeably shorter than the 1024 characters YAML allows.	1272	noticeably shorter than the 1024 "stream characters" YAML allows and that
		1273	you do not have characters with codepoint values outside the Unicode BMP
		1274	(basic multilingual page). YAML also does not allow C<\/> sequences in
		1275	strings (which JSON::XS does not I<currently> generate, but other JSON
		1276	generators might).
900		1277
901	There might be other incompatibilities that I am not aware of. In general	1278	There might be other incompatibilities that I am not aware of (or the YAML
		1279	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,	1280	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	1281	versa, or try to parse JSON with a YAML parser or vice versa: chances are
904	that you will run into severe interoperability problems.	1282	high that you will run into severe interoperability problems when you
		1283	least expect it.
		1284
		1285	=over 4
		1286
		1287	=item (*)
		1288
		1289	I have been pressured multiple times by Brian Ingerson (one of the
		1290	authors of the YAML specification) to remove this paragraph, despite him
		1291	acknowledging that the actual incompatibilities exist. As I was personally
		1292	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1293	educate people about these issues, so others do not run into the same
		1294	problem again and again. After this, Brian called me a (quote)I<complete
		1295	and worthless idiot>(unquote).
		1296
		1297	In my opinion, instead of pressuring and insulting people who actually
		1298	clarify issues with YAML and the wrong statements of some of its
		1299	proponents, I would kindly suggest reading the JSON spec (which is not
		1300	that difficult or long) and finally make YAML compatible to it, and
		1301	educating users about the changes, instead of spreading lies about the
		1302	real compatibility for many I<years> and trying to silence people who
		1303	point out that it isn't true.
		1304
		1305	=back
905		1306
906		1307
907	=head2 SPEED	1308	=head2 SPEED
908		1309
909	It seems that JSON::XS is surprisingly fast, as shown in the following	1310	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	1311	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	1312	in the JSON::XS distribution, to make it easy to compare on your own
912	system.	1313	system.
913		1314
914	First comes a comparison between various modules using a very short	1315	First comes a comparison between various modules using
915	single-line JSON string:	1316	a very short single-line JSON string (also available at
		1317	L<http://dist.schmorp.de/misc/json/short.json>).
916		1318
917	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1319	{"method": "handleMessage", "params": ["user1",
918	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1320	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1321	true, false]}
919		1322
920	It shows the number of encodes/decodes per second (JSON::XS uses	1323	It shows the number of encodes/decodes per second (JSON::XS uses
921	the functional interface, while JSON::XS/2 uses the OO interface	1324	the functional interface, while JSON::XS/2 uses the OO interface
922	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1325	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
923	shrink). Higher is better:	1326	shrink). Higher is better:
…		…
939	about three times faster on decoding, and over forty times faster	1342	about three times faster on decoding, and over forty times faster
940	than JSON, even with pretty-printing and key sorting. It also compares	1343	than JSON, even with pretty-printing and key sorting. It also compares
941	favourably to Storable for small amounts of data.	1344	favourably to Storable for small amounts of data.
942		1345
943	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1346	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
944	search API (http://nanoref.com/yahooapis/mgPdGg):	1347	search API (L<http://dist.schmorp.de/misc/json/long.json>).
945		1348
946	module \| encode \| decode \|	1349	module \| encode \| decode \|
947	-----------\|------------\|------------\|	1350	-----------\|------------\|------------\|
948	JSON 1.x \| 55.260 \| 34.971 \|	1351	JSON 1.x \| 55.260 \| 34.971 \|
949	JSON::DWIW \| 825.228 \| 1082.513 \|	1352	JSON::DWIW \| 825.228 \| 1082.513 \|
…		…
986		1389
987	Third, JSON::XS recurses using the C stack when decoding objects and	1390	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	1391	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	1392	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	1393	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	1394	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	1395	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	1396	has a smaller stack, you should adjust this setting accordingly with the
994	C<max_depth> method.	1397	C<max_depth> method.
995		1398
996	And last but least, something else could bomb you that I forgot to think	1399	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,	1400	case, you get to keep the pieces. I am always open for hints, though...
998	though...	1401
		1402	Also keep in mind that JSON::XS might leak contents of your Perl data
		1403	structures in its error messages, so when you serialise sensitive
		1404	information you might want to make sure that exceptions thrown by JSON::XS
		1405	will not end up in front of untrusted eyes.
999		1406
1000	If you are using JSON::XS to return packets to consumption	1407	If you are using JSON::XS to return packets to consumption
1001	by JavaScript scripts in a browser you should have a look at	1408	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	1409	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
1003	you are vulnerable to some common attack vectors (which really are browser	1410	you are vulnerable to some common attack vectors (which really are browser
1004	design bugs, but it is still you who will have to deal with it, as major	1411	design bugs, but it is still you who will have to deal with it, as major
1005	browser developers care only for features, not about doing security	1412	browser developers care only for features, not about getting security
1006	right).	1413	right).
1007		1414
1008		1415
1009	=head1 THREADS	1416	=head1 THREADS
1010		1417
1011	This module is I<not> guaranteed to be thread safe and there are no	1418	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	1419	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	1420	horribly slow so-called "threads" which are simply slow and bloated
1014	process simulations - use fork, its I<much> faster, cheaper, better).	1421	process simulations - use fork, it's I<much> faster, cheaper, better).
1015		1422
1016	(It might actually work, but you have been warned).	1423	(It might actually work, but you have been warned).
1017		1424
1018		1425
1019	=head1 BUGS	1426	=head1 BUGS
1020		1427
1021	While the goal of this module is to be correct, that unfortunately does	1428	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	1429	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	1430	keep reporting bugs they will be fixed swiftly, though.
1024	will be fixed swiftly, though.
1025		1431
1026	Please refrain from using rt.cpan.org or any other bug reporting	1432	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.	1433	service. I put the contact address into my modules for a reason.
1028		1434
1029	=cut	1435	=cut
…		…
1049	"--" => sub { $_[0] = ${$_[0]} - 1 },	1455	"--" => sub { $_[0] = ${$_[0]} - 1 },
1050	fallback => 1;	1456	fallback => 1;
1051		1457
1052	1;	1458	1;
1053		1459
		1460	=head1 SEE ALSO
		1461
		1462	The F<json_xs> command line utility for quick experiments.
		1463
1054	=head1 AUTHOR	1464	=head1 AUTHOR
1055		1465
1056	Marc Lehmann <schmorp@schmorp.de>	1466	Marc Lehmann <schmorp@schmorp.de>
1057	http://home.schmorp.de/	1467	http://home.schmorp.de/
1058		1468

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Revision 1.121 by root, Mon Jul 13 22:13:17 2009 UTC