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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.75 by root, Thu Nov 29 13:35:35 2007 UTC vs.
Revision 1.138 by root, Wed Aug 1 19:04:41 2012 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 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 = '2.0';	106	our $VERSION = '2.33';
90	our @ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
91		108
92	our @EXPORT = qw(to_json from_json);	109	our @EXPORT = qw(encode_json decode_json to_json from_json);
		110
		111	sub to_json($) {
		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<$enable> is false, then the C<encode> method will not escape Unicode
240	characters unless required by the JSON syntax or other flags.	270	characters unless required by the JSON syntax or other flags.
		271
		272	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		273	document.
241		274
242	The main use for this flag is efficiently encoding binary data as JSON	275	The main use for this flag is efficiently encoding binary data as JSON
243	text, as most octets will not be escaped, resulting in a smaller encoded	276	text, as most octets will not be escaped, resulting in a smaller encoded
244	size. The disadvantage is that the resulting JSON text is encoded	277	size. The disadvantage is that the resulting JSON text is encoded
245	in latin1 (and must correctly be treated as such when storing and	278	in latin1 (and must correctly be treated as such when storing and
…		…
264		297
265	If C<$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.
		302
		303	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		304	document.
269		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);
…		…
405	the same hash might be encoded differently even if contains the same data,	441	the same hash might be encoded differently even if contains the same data,
406	as key-value pairs have no inherent ordering in Perl.	442	as key-value pairs have no inherent ordering in Perl.
407		443
408	This setting has no effect when decoding JSON texts.	444	This setting has no effect when decoding JSON texts.
409		445
		446	This setting has currently no effect on tied hashes.
		447
410	=item $json = $json->allow_nonref ([$enable])	448	=item $json = $json->allow_nonref ([$enable])
411		449
412	=item $enabled = $json->get_allow_nonref	450	=item $enabled = $json->get_allow_nonref
413		451
414	If C<$enable> is true (or missing), then the C<encode> method can convert a	452	If C<$enable> is true (or missing), then the C<encode> method can convert a
…		…
425	resulting in an invalid JSON text:	463	resulting in an invalid JSON text:
426		464
427	JSON::XS->new->allow_nonref->encode ("Hello, World!")	465	JSON::XS->new->allow_nonref->encode ("Hello, World!")
428	=> "Hello, World!"	466	=> "Hello, World!"
429		467
		468	=item $json = $json->allow_unknown ([$enable])
		469
		470	=item $enabled = $json->get_allow_unknown
		471
		472	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		473	exception when it encounters values it cannot represent in JSON (for
		474	example, filehandles) but instead will encode a JSON C<null> value. Note
		475	that blessed objects are not included here and are handled separately by
		476	c<allow_nonref>.
		477
		478	If C<$enable> is false (the default), then C<encode> will throw an
		479	exception when it encounters anything it cannot encode as JSON.
		480
		481	This option does not affect C<decode> in any way, and it is recommended to
		482	leave it off unless you know your communications partner.
		483
430	=item $json = $json->allow_blessed ([$enable])	484	=item $json = $json->allow_blessed ([$enable])
431		485
432	=item $enabled = $json->get_allow_blessed	486	=item $enabled = $json->get_allow_blessed
433		487
434	If C<$enable> is true (or missing), then the C<encode> method will not	488	If C<$enable> is true (or missing), then the C<encode> method will not
435	barf when it encounters a blessed reference. Instead, the value of the	489	barf when it encounters a blessed reference. Instead, the value of the
436	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>	490	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
437	disabled or no C<to_json> method found) or a representation of the	491	disabled or no C<TO_JSON> method found) or a representation of the
438	object (C<convert_blessed> enabled and C<to_json> method found) is being	492	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
439	encoded. Has no effect on C<decode>.	493	encoded. Has no effect on C<decode>.
440		494
441	If C<$enable> is false (the default), then C<encode> will throw an	495	If C<$enable> is false (the default), then C<encode> will throw an
442	exception when it encounters a blessed object.	496	exception when it encounters a blessed object.
443		497
…		…
455	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>	509	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
456	returns other blessed objects, those will be handled in the same	510	returns other blessed objects, those will be handled in the same
457	way. C<TO_JSON> must take care of not causing an endless recursion cycle	511	way. C<TO_JSON> must take care of not causing an endless recursion cycle
458	(== crash) in this case. The name of C<TO_JSON> was chosen because other	512	(== crash) in this case. The name of C<TO_JSON> was chosen because other
459	methods called by the Perl core (== not by the user of the object) are	513	methods called by the Perl core (== not by the user of the object) are
460	usually in upper case letters and to avoid collisions with the C<to_json>	514	usually in upper case letters and to avoid collisions with any C<to_json>
461	function.	515	function or method.
462		516
463	This setting does not yet influence C<decode> in any way, but in the	517	This setting does not yet influence C<decode> in any way, but in the
464	future, global hooks might get installed that influence C<decode> and are	518	future, global hooks might get installed that influence C<decode> and are
465	enabled by this setting.	519	enabled by this setting.
466		520
…		…
574	=item $json = $json->max_depth ([$maximum_nesting_depth])	628	=item $json = $json->max_depth ([$maximum_nesting_depth])
575		629
576	=item $max_depth = $json->get_max_depth	630	=item $max_depth = $json->get_max_depth
577		631
578	Sets the maximum nesting level (default C<512>) accepted while encoding	632	Sets the maximum nesting level (default C<512>) accepted while encoding
579	or decoding. If the JSON text or Perl data structure has an equal or	633	or decoding. If a higher nesting level is detected in JSON text or a Perl
580	higher nesting level then this limit, then the encoder and decoder will	634	data structure, then the encoder and decoder will stop and croak at that
581	stop and croak at that point.	635	point.
582		636
583	Nesting level is defined by number of hash- or arrayrefs that the encoder	637	Nesting level is defined by number of hash- or arrayrefs that the encoder
584	needs to traverse to reach a given point or the number of C<{> or C<[>	638	needs to traverse to reach a given point or the number of C<{> or C<[>
585	characters without their matching closing parenthesis crossed to reach a	639	characters without their matching closing parenthesis crossed to reach a
586	given character in a string.	640	given character in a string.
587		641
588	Setting the maximum depth to one disallows any nesting, so that ensures	642	Setting the maximum depth to one disallows any nesting, so that ensures
589	that the object is only a single hash/object or array.	643	that the object is only a single hash/object or array.
590		644
591	The argument to C<max_depth> will be rounded up to the next highest power
592	of two. If no argument is given, the highest possible setting will be	645	If no argument is given, the highest possible setting will be used, which
593	used, which is rarely useful.	646	is rarely useful.
		647
		648	Note that nesting is implemented by recursion in C. The default value has
		649	been chosen to be as large as typical operating systems allow without
		650	crashing.
594		651
595	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	652	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
596		653
597	=item $json = $json->max_size ([$maximum_string_size])	654	=item $json = $json->max_size ([$maximum_string_size])
598		655
599	=item $max_size = $json->get_max_size	656	=item $max_size = $json->get_max_size
600		657
601	Set the maximum length a JSON text may have (in bytes) where decoding is	658	Set the maximum length a JSON text may have (in bytes) where decoding is
602	being attempted. The default is C<0>, meaning no limit. When C<decode>	659	being attempted. The default is C<0>, meaning no limit. When C<decode>
603	is called on a string longer then this number of characters it will not	660	is called on a string that is longer then this many bytes, it will not
604	attempt to decode the string but throw an exception. This setting has no	661	attempt to decode the string but throw an exception. This setting has no
605	effect on C<encode> (yet).	662	effect on C<encode> (yet).
606		663
607	The argument to C<max_size> will be rounded up to the next B<highest>	664	If no argument is given, the limit check will be deactivated (same as when
608	power of two (so may be more than requested). If no argument is given, the	665	C<0> is specified).
609	limit check will be deactivated (same as when C<0> is specified).
610		666
611	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	667	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
612		668
613	=item $json_text = $json->encode ($perl_scalar)	669	=item $json_text = $json->encode ($perl_scalar)
614		670
…		…
643	=> ([], 3)	699	=> ([], 3)
644		700
645	=back	701	=back
646		702
647		703
		704	=head1 INCREMENTAL PARSING
		705
		706	In some cases, there is the need for incremental parsing of JSON
		707	texts. While this module always has to keep both JSON text and resulting
		708	Perl data structure in memory at one time, it does allow you to parse a
		709	JSON stream incrementally. It does so by accumulating text until it has
		710	a full JSON object, which it then can decode. This process is similar to
		711	using C<decode_prefix> to see if a full JSON object is available, but
		712	is much more efficient (and can be implemented with a minimum of method
		713	calls).
		714
		715	JSON::XS will only attempt to parse the JSON text once it is sure it
		716	has enough text to get a decisive result, using a very simple but
		717	truly incremental parser. This means that it sometimes won't stop as
		718	early as the full parser, for example, it doesn't detect mismatched
		719	parentheses. The only thing it guarantees is that it starts decoding as
		720	soon as a syntactically valid JSON text has been seen. This means you need
		721	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		722	parsing in the presence if syntax errors.
		723
		724	The following methods implement this incremental parser.
		725
		726	=over 4
		727
		728	=item [void, scalar or list context] = $json->incr_parse ([$string])
		729
		730	This is the central parsing function. It can both append new text and
		731	extract objects from the stream accumulated so far (both of these
		732	functions are optional).
		733
		734	If C<$string> is given, then this string is appended to the already
		735	existing JSON fragment stored in the C<$json> object.
		736
		737	After that, if the function is called in void context, it will simply
		738	return without doing anything further. This can be used to add more text
		739	in as many chunks as you want.
		740
		741	If the method is called in scalar context, then it will try to extract
		742	exactly I<one> JSON object. If that is successful, it will return this
		743	object, otherwise it will return C<undef>. If there is a parse error,
		744	this method will croak just as C<decode> would do (one can then use
		745	C<incr_skip> to skip the errornous part). This is the most common way of
		746	using the method.
		747
		748	And finally, in list context, it will try to extract as many objects
		749	from the stream as it can find and return them, or the empty list
		750	otherwise. For this to work, there must be no separators between the JSON
		751	objects or arrays, instead they must be concatenated back-to-back. If
		752	an error occurs, an exception will be raised as in the scalar context
		753	case. Note that in this case, any previously-parsed JSON texts will be
		754	lost.
		755
		756	Example: Parse some JSON arrays/objects in a given string and return
		757	them.
		758
		759	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		760
		761	=item $lvalue_string = $json->incr_text
		762
		763	This method returns the currently stored JSON fragment as an lvalue, that
		764	is, you can manipulate it. This I<only> works when a preceding call to
		765	C<incr_parse> in I<scalar context> successfully returned an object. Under
		766	all other circumstances you must not call this function (I mean it.
		767	although in simple tests it might actually work, it I<will> fail under
		768	real world conditions). As a special exception, you can also call this
		769	method before having parsed anything.
		770
		771	This function is useful in two cases: a) finding the trailing text after a
		772	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		773	(such as commas).
		774
		775	=item $json->incr_skip
		776
		777	This will reset the state of the incremental parser and will remove
		778	the parsed text from the input buffer so far. This is useful after
		779	C<incr_parse> died, in which case the input buffer and incremental parser
		780	state is left unchanged, to skip the text parsed so far and to reset the
		781	parse state.
		782
		783	The difference to C<incr_reset> is that only text until the parse error
		784	occured is removed.
		785
		786	=item $json->incr_reset
		787
		788	This completely resets the incremental parser, that is, after this call,
		789	it will be as if the parser had never parsed anything.
		790
		791	This is useful if you want to repeatedly parse JSON objects and want to
		792	ignore any trailing data, which means you have to reset the parser after
		793	each successful decode.
		794
		795	=back
		796
		797	=head2 LIMITATIONS
		798
		799	All options that affect decoding are supported, except
		800	C<allow_nonref>. The reason for this is that it cannot be made to
		801	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		802	them back to back and still decode them perfectly. This does not hold true
		803	for JSON numbers, however.
		804
		805	For example, is the string C<1> a single JSON number, or is it simply the
		806	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		807	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		808	takes the conservative route and disallows this case.
		809
		810	=head2 EXAMPLES
		811
		812	Some examples will make all this clearer. First, a simple example that
		813	works similarly to C<decode_prefix>: We want to decode the JSON object at
		814	the start of a string and identify the portion after the JSON object:
		815
		816	my $text = "[1,2,3] hello";
		817
		818	my $json = new JSON::XS;
		819
		820	my $obj = $json->incr_parse ($text)
		821	or die "expected JSON object or array at beginning of string";
		822
		823	my $tail = $json->incr_text;
		824	# $tail now contains " hello"
		825
		826	Easy, isn't it?
		827
		828	Now for a more complicated example: Imagine a hypothetical protocol where
		829	you read some requests from a TCP stream, and each request is a JSON
		830	array, without any separation between them (in fact, it is often useful to
		831	use newlines as "separators", as these get interpreted as whitespace at
		832	the start of the JSON text, which makes it possible to test said protocol
		833	with C<telnet>...).
		834
		835	Here is how you'd do it (it is trivial to write this in an event-based
		836	manner):
		837
		838	my $json = new JSON::XS;
		839
		840	# read some data from the socket
		841	while (sysread $socket, my $buf, 4096) {
		842
		843	# split and decode as many requests as possible
		844	for my $request ($json->incr_parse ($buf)) {
		845	# act on the $request
		846	}
		847	}
		848
		849	Another complicated example: Assume you have a string with JSON objects
		850	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		851	[3]>). To parse them, we have to skip the commas between the JSON texts,
		852	and here is where the lvalue-ness of C<incr_text> comes in useful:
		853
		854	my $text = "[1],[2], [3]";
		855	my $json = new JSON::XS;
		856
		857	# void context, so no parsing done
		858	$json->incr_parse ($text);
		859
		860	# now extract as many objects as possible. note the
		861	# use of scalar context so incr_text can be called.
		862	while (my $obj = $json->incr_parse) {
		863	# do something with $obj
		864
		865	# now skip the optional comma
		866	$json->incr_text =~ s/^ \s* , //x;
		867	}
		868
		869	Now lets go for a very complex example: Assume that you have a gigantic
		870	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		871	but you cannot load it into memory fully (this has actually happened in
		872	the real world :).
		873
		874	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		875	can still help you: You implement a (very simple) array parser and let
		876	JSON decode the array elements, which are all full JSON objects on their
		877	own (this wouldn't work if the array elements could be JSON numbers, for
		878	example):
		879
		880	my $json = new JSON::XS;
		881
		882	# open the monster
		883	open my $fh, "<bigfile.json"
		884	or die "bigfile: $!";
		885
		886	# first parse the initial "["
		887	for (;;) {
		888	sysread $fh, my $buf, 65536
		889	or die "read error: $!";
		890	$json->incr_parse ($buf); # void context, so no parsing
		891
		892	# Exit the loop once we found and removed(!) the initial "[".
		893	# In essence, we are (ab-)using the $json object as a simple scalar
		894	# we append data to.
		895	last if $json->incr_text =~ s/^ \s* \[ //x;
		896	}
		897
		898	# now we have the skipped the initial "[", so continue
		899	# parsing all the elements.
		900	for (;;) {
		901	# in this loop we read data until we got a single JSON object
		902	for (;;) {
		903	if (my $obj = $json->incr_parse) {
		904	# do something with $obj
		905	last;
		906	}
		907
		908	# add more data
		909	sysread $fh, my $buf, 65536
		910	or die "read error: $!";
		911	$json->incr_parse ($buf); # void context, so no parsing
		912	}
		913
		914	# in this loop we read data until we either found and parsed the
		915	# separating "," between elements, or the final "]"
		916	for (;;) {
		917	# first skip whitespace
		918	$json->incr_text =~ s/^\s*//;
		919
		920	# if we find "]", we are done
		921	if ($json->incr_text =~ s/^\]//) {
		922	print "finished.\n";
		923	exit;
		924	}
		925
		926	# if we find ",", we can continue with the next element
		927	if ($json->incr_text =~ s/^,//) {
		928	last;
		929	}
		930
		931	# if we find anything else, we have a parse error!
		932	if (length $json->incr_text) {
		933	die "parse error near ", $json->incr_text;
		934	}
		935
		936	# else add more data
		937	sysread $fh, my $buf, 65536
		938	or die "read error: $!";
		939	$json->incr_parse ($buf); # void context, so no parsing
		940	}
		941
		942	This is a complex example, but most of the complexity comes from the fact
		943	that we are trying to be correct (bear with me if I am wrong, I never ran
		944	the above example :).
		945
		946
		947
648	=head1 MAPPING	948	=head1 MAPPING
649		949
650	This section describes how JSON::XS maps Perl values to JSON values and	950	This section describes how JSON::XS maps Perl values to JSON values and
651	vice versa. These mappings are designed to "do the right thing" in most	951	vice versa. These mappings are designed to "do the right thing" in most
652	circumstances automatically, preserving round-tripping characteristics	952	circumstances automatically, preserving round-tripping characteristics
…		…
680		980
681	A JSON number becomes either an integer, numeric (floating point) or	981	A JSON number becomes either an integer, numeric (floating point) or
682	string scalar in perl, depending on its range and any fractional parts. On	982	string scalar in perl, depending on its range and any fractional parts. On
683	the Perl level, there is no difference between those as Perl handles all	983	the Perl level, there is no difference between those as Perl handles all
684	the conversion details, but an integer may take slightly less memory and	984	the conversion details, but an integer may take slightly less memory and
685	might represent more values exactly than (floating point) numbers.	985	might represent more values exactly than floating point numbers.
686		986
687	If the number consists of digits only, JSON::XS will try to represent	987	If the number consists of digits only, JSON::XS will try to represent
688	it as an integer value. If that fails, it will try to represent it as	988	it as an integer value. If that fails, it will try to represent it as
689	a numeric (floating point) value if that is possible without loss of	989	a numeric (floating point) value if that is possible without loss of
690	precision. Otherwise it will preserve the number as a string value.	990	precision. Otherwise it will preserve the number as a string value (in
		991	which case you lose roundtripping ability, as the JSON number will be
		992	re-encoded toa JSON string).
691		993
692	Numbers containing a fractional or exponential part will always be	994	Numbers containing a fractional or exponential part will always be
693	represented as numeric (floating point) values, possibly at a loss of	995	represented as numeric (floating point) values, possibly at a loss of
694	precision.	996	precision (in which case you might lose perfect roundtripping ability, but
		997	the JSON number will still be re-encoded as a JSON number).
695		998
696	This might create round-tripping problems as numbers might become strings,	999	Note that precision is not accuracy - binary floating point values cannot
697	but as Perl is typeless there is no other way to do it.	1000	represent most decimal fractions exactly, and when converting from and to
		1001	floating point, JSON::XS only guarantees precision up to but not including
		1002	the leats significant bit.
698		1003
699	=item true, false	1004	=item true, false
700		1005
701	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	1006	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
702	respectively. They are overloaded to act almost exactly like the numbers	1007	respectively. They are overloaded to act almost exactly like the numbers
…		…
739	Other unblessed references are generally not allowed and will cause an	1044	Other unblessed references are generally not allowed and will cause an
740	exception to be thrown, except for references to the integers C<0> and	1045	exception to be thrown, except for references to the integers C<0> and
741	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	1046	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
742	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.	1047	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
743		1048
744	to_json [\0,JSON::XS::true] # yields [false,true]	1049	encode_json [\0, JSON::XS::true] # yields [false,true]
745		1050
746	=item JSON::XS::true, JSON::XS::false	1051	=item JSON::XS::true, JSON::XS::false
747		1052
748	These special values become JSON true and JSON false values,	1053	These special values become JSON true and JSON false values,
749	respectively. You can also use C<\1> and C<\0> directly if you want.	1054	respectively. You can also use C<\1> and C<\0> directly if you want.
750		1055
751	=item blessed objects	1056	=item blessed objects
752		1057
753	Blessed objects are not allowed. JSON::XS currently tries to encode their	1058	Blessed objects are not directly representable in JSON. See the
754	underlying representation (hash- or arrayref), but this behaviour might	1059	C<allow_blessed> and C<convert_blessed> methods on various options on
755	change in future versions.	1060	how to deal with this: basically, you can choose between throwing an
		1061	exception, encoding the reference as if it weren't blessed, or provide
		1062	your own serialiser method.
756		1063
757	=item simple scalars	1064	=item simple scalars
758		1065
759	Simple Perl scalars (any scalar that is not a reference) are the most	1066	Simple Perl scalars (any scalar that is not a reference) are the most
760	difficult objects to encode: JSON::XS will encode undefined scalars as	1067	difficult objects to encode: JSON::XS will encode undefined scalars as
761	JSON null value, scalars that have last been used in a string context	1068	JSON C<null> values, scalars that have last been used in a string context
762	before encoding as JSON strings and anything else as number value:	1069	before encoding as JSON strings, and anything else as number value:
763		1070
764	# dump as number	1071	# dump as number
765	to_json [2] # yields [2]	1072	encode_json [2] # yields [2]
766	to_json [-3.0e17] # yields [-3e+17]	1073	encode_json [-3.0e17] # yields [-3e+17]
767	my $value = 5; to_json [$value] # yields [5]	1074	my $value = 5; encode_json [$value] # yields [5]
768		1075
769	# used as string, so dump as string	1076	# used as string, so dump as string
770	print $value;	1077	print $value;
771	to_json [$value] # yields ["5"]	1078	encode_json [$value] # yields ["5"]
772		1079
773	# undef becomes null	1080	# undef becomes null
774	to_json [undef] # yields [null]	1081	encode_json [undef] # yields [null]
775		1082
776	You can force the type to be a JSON string by stringifying it:	1083	You can force the type to be a JSON string by stringifying it:
777		1084
778	my $x = 3.1; # some variable containing a number	1085	my $x = 3.1; # some variable containing a number
779	"$x"; # stringified	1086	"$x"; # stringified
…		…
785	my $x = "3"; # some variable containing a string	1092	my $x = "3"; # some variable containing a string
786	$x += 0; # numify it, ensuring it will be dumped as a number	1093	$x += 0; # numify it, ensuring it will be dumped as a number
787	$x *= 1; # same thing, the choice is yours.	1094	$x *= 1; # same thing, the choice is yours.
788		1095
789	You can not currently force the type in other, less obscure, ways. Tell me	1096	You can not currently force the type in other, less obscure, ways. Tell me
790	if you need this capability.	1097	if you need this capability (but don't forget to explain why it's needed
		1098	:).
		1099
		1100	Note that numerical precision has the same meaning as under Perl (so
		1101	binary to decimal conversion follows the same rules as in Perl, which
		1102	can differ to other languages). Also, your perl interpreter might expose
		1103	extensions to the floating point numbers of your platform, such as
		1104	infinities or NaN's - these cannot be represented in JSON, and it is an
		1105	error to pass those in.
791		1106
792	=back	1107	=back
793		1108
794		1109
795	=head1 COMPARISON	1110	=head1 ENCODING/CODESET FLAG NOTES
796		1111
797	As already mentioned, this module was created because none of the existing	1112	The interested reader might have seen a number of flags that signify
798	JSON modules could be made to work correctly. First I will describe the	1113	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
799	problems (or pleasures) I encountered with various existing JSON modules,	1114	some confusion on what these do, so here is a short comparison:
800	followed by some benchmark values. JSON::XS was designed not to suffer	1115
801	from any of these problems or limitations.	1116	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1117	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1118	control whether C<encode> escapes character values outside their respective
		1119	codeset range. Neither of these flags conflict with each other, although
		1120	some combinations make less sense than others.
		1121
		1122	Care has been taken to make all flags symmetrical with respect to
		1123	C<encode> and C<decode>, that is, texts encoded with any combination of
		1124	these flag values will be correctly decoded when the same flags are used
		1125	- in general, if you use different flag settings while encoding vs. when
		1126	decoding you likely have a bug somewhere.
		1127
		1128	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1129	simply an abstract set of character-codepoint pairs, while an encoding
		1130	takes those codepoint numbers and I<encodes> them, in our case into
		1131	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1132	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1133	the same time, which can be confusing.
802		1134
803	=over 4	1135	=over 4
804		1136
805	=item JSON 1.07	1137	=item C<utf8> flag disabled
806		1138
807	Slow (but very portable, as it is written in pure Perl).	1139	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1140	and expect Unicode strings, that is, characters with high ordinal Unicode
		1141	values (> 255) will be encoded as such characters, and likewise such
		1142	characters are decoded as-is, no canges to them will be done, except
		1143	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1144	respectively (to Perl, these are the same thing in strings unless you do
		1145	funny/weird/dumb stuff).
808		1146
809	Undocumented/buggy Unicode handling (how JSON handles Unicode values is	1147	This is useful when you want to do the encoding yourself (e.g. when you
810	undocumented. One can get far by feeding it Unicode strings and doing	1148	want to have UTF-16 encoded JSON texts) or when some other layer does
811	en-/decoding oneself, but Unicode escapes are not working properly).	1149	the encoding for you (for example, when printing to a terminal using a
		1150	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1151	to UTF-8 encode your data first and have Perl encode it another time).
812		1152
813	No round-tripping (strings get clobbered if they look like numbers, e.g.	1153	=item C<utf8> flag enabled
814	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
815	decode into the number 2.
816		1154
817	=item JSON::PC 0.01	1155	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1156	characters using the corresponding UTF-8 multi-byte sequence, and will
		1157	expect your input strings to be encoded as UTF-8, that is, no "character"
		1158	of the input string must have any value > 255, as UTF-8 does not allow
		1159	that.
818		1160
819	Very fast.	1161	The C<utf8> flag therefore switches between two modes: disabled means you
		1162	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1163	octet/binary string in Perl.
820		1164
821	Undocumented/buggy Unicode handling.	1165	=item C<latin1> or C<ascii> flags enabled
822		1166
823	No round-tripping.	1167	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1168	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1169	characters as specified by the C<utf8> flag.
824		1170
825	Has problems handling many Perl values (e.g. regex results and other magic	1171	If C<utf8> is disabled, then the result is also correctly encoded in those
826	values will make it croak).	1172	character sets (as both are proper subsets of Unicode, meaning that a
		1173	Unicode string with all character values < 256 is the same thing as a
		1174	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1175	the same thing as an ASCII string in Perl).
827		1176
828	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1177	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
829	which is not a valid JSON text.	1178	regardless of these flags, just some more characters will be escaped using
		1179	C<\uXXXX> then before.
830		1180
831	Unmaintained (maintainer unresponsive for many months, bugs are not	1181	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
832	getting fixed).	1182	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1183	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1184	a subset of Unicode), while ASCII is.
833		1185
834	=item JSON::Syck 0.21	1186	Surprisingly, C<decode> will ignore these flags and so treat all input
		1187	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1188	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1189	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
835		1190
836	Very buggy (often crashes).	1191	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1192	they only govern when the JSON output engine escapes a character or not.
837		1193
838	Very inflexible (no human-readable format supported, format pretty much	1194	The main use for C<latin1> is to relatively efficiently store binary data
839	undocumented. I need at least a format for easy reading by humans and a	1195	as JSON, at the expense of breaking compatibility with most JSON decoders.
840	single-line compact format for use in a protocol, and preferably a way to
841	generate ASCII-only JSON texts).
842		1196
843	Completely broken (and confusingly documented) Unicode handling (Unicode	1197	The main use for C<ascii> is to force the output to not contain characters
844	escapes are not working properly, you need to set ImplicitUnicode to	1198	with values > 127, which means you can interpret the resulting string
845	I<different> values on en- and decoding to get symmetric behaviour).	1199	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
846		1200	8-bit-encoding, and still get the same data structure back. This is useful
847	No round-tripping (simple cases work, but this depends on whether the scalar	1201	when your channel for JSON transfer is not 8-bit clean or the encoding
848	value was used in a numeric context or not).	1202	might be mangled in between (e.g. in mail), and works because ASCII is a
849		1203	proper subset of most 8-bit and multibyte encodings in use in the world.
850	Dumping hashes may skip hash values depending on iterator state.
851
852	Unmaintained (maintainer unresponsive for many months, bugs are not
853	getting fixed).
854
855	Does not check input for validity (i.e. will accept non-JSON input and
856	return "something" instead of raising an exception. This is a security
857	issue: imagine two banks transferring money between each other using
858	JSON. One bank might parse a given non-JSON request and deduct money,
859	while the other might reject the transaction with a syntax error. While a
860	good protocol will at least recover, that is extra unnecessary work and
861	the transaction will still not succeed).
862
863	=item JSON::DWIW 0.04
864
865	Very fast. Very natural. Very nice.
866
867	Undocumented Unicode handling (but the best of the pack. Unicode escapes
868	still don't get parsed properly).
869
870	Very inflexible.
871
872	No round-tripping.
873
874	Does not generate valid JSON texts (key strings are often unquoted, empty keys
875	result in nothing being output)
876
877	Does not check input for validity.
878		1204
879	=back	1205	=back
880		1206
881		1207
		1208	=head2 JSON and ECMAscript
		1209
		1210	JSON syntax is based on how literals are represented in javascript (the
		1211	not-standardised predecessor of ECMAscript) which is presumably why it is
		1212	called "JavaScript Object Notation".
		1213
		1214	However, JSON is not a subset (and also not a superset of course) of
		1215	ECMAscript (the standard) or javascript (whatever browsers actually
		1216	implement).
		1217
		1218	If you want to use javascript's C<eval> function to "parse" JSON, you
		1219	might run into parse errors for valid JSON texts, or the resulting data
		1220	structure might not be queryable:
		1221
		1222	One of the problems is that U+2028 and U+2029 are valid characters inside
		1223	JSON strings, but are not allowed in ECMAscript string literals, so the
		1224	following Perl fragment will not output something that can be guaranteed
		1225	to be parsable by javascript's C<eval>:
		1226
		1227	use JSON::XS;
		1228
		1229	print encode_json [chr 0x2028];
		1230
		1231	The right fix for this is to use a proper JSON parser in your javascript
		1232	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1233	F<json2.js> parser).
		1234
		1235	If this is not an option, you can, as a stop-gap measure, simply encode to
		1236	ASCII-only JSON:
		1237
		1238	use JSON::XS;
		1239
		1240	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1241
		1242	Note that this will enlarge the resulting JSON text quite a bit if you
		1243	have many non-ASCII characters. You might be tempted to run some regexes
		1244	to only escape U+2028 and U+2029, e.g.:
		1245
		1246	# DO NOT USE THIS!
		1247	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1248	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1249	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1250	print $json;
		1251
		1252	Note that I<this is a bad idea>: the above only works for U+2028 and
		1253	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1254	javascript implementations, however, have issues with other characters as
		1255	well - using C<eval> naively simply I<will> cause problems.
		1256
		1257	Another problem is that some javascript implementations reserve
		1258	some property names for their own purposes (which probably makes
		1259	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1260	C<__proto__> property name for its own purposes.
		1261
		1262	If that is a problem, you could parse try to filter the resulting JSON
		1263	output for these property strings, e.g.:
		1264
		1265	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1266
		1267	This works because C<__proto__> is not valid outside of strings, so every
		1268	occurence of C<"__proto__"\s*:> must be a string used as property name.
		1269
		1270	If you know of other incompatibilities, please let me know.
		1271
		1272
882	=head2 JSON and YAML	1273	=head2 JSON and YAML
883		1274
884	You often hear that JSON is a subset (or a close subset) of YAML. This is,	1275	You often hear that JSON is a subset of YAML. This is, however, a mass
885	however, a mass hysteria and very far from the truth. In general, there is	1276	hysteria(*) and very far from the truth (as of the time of this writing),
886	no way to configure JSON::XS to output a data structure as valid YAML.	1277	so let me state it clearly: I<in general, there is no way to configure
		1278	JSON::XS to output a data structure as valid YAML> that works in all
		1279	cases.
887		1280
888	If you really must use JSON::XS to generate YAML, you should use this	1281	If you really must use JSON::XS to generate YAML, you should use this
889	algorithm (subject to change in future versions):	1282	algorithm (subject to change in future versions):
890		1283
891	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1284	my $to_yaml = JSON::XS->new->utf8->space_after (1);
892	my $yaml = $to_yaml->encode ($ref) . "\n";	1285	my $yaml = $to_yaml->encode ($ref) . "\n";
893		1286
894	This will usually generate JSON texts that also parse as valid	1287	This will I<usually> generate JSON texts that also parse as valid
895	YAML. Please note that YAML has hardcoded limits on (simple) object key	1288	YAML. Please note that YAML has hardcoded limits on (simple) object key
896	lengths that JSON doesn't have, so you should make sure that your hash	1289	lengths that JSON doesn't have and also has different and incompatible
		1290	unicode character escape syntax, so you should make sure that your hash
897	keys are noticeably shorter than the 1024 characters YAML allows.	1291	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1292	and that you do not have characters with codepoint values outside the
		1293	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1294	sequences in strings (which JSON::XS does not I<currently> generate, but
		1295	other JSON generators might).
898		1296
899	There might be other incompatibilities that I am not aware of. In general	1297	There might be other incompatibilities that I am not aware of (or the YAML
		1298	specification has been changed yet again - it does so quite often). In
900	you should not try to generate YAML with a JSON generator or vice versa,	1299	general you should not try to generate YAML with a JSON generator or vice
901	or try to parse JSON with a YAML parser or vice versa: chances are high	1300	versa, or try to parse JSON with a YAML parser or vice versa: chances are
902	that you will run into severe interoperability problems.	1301	high that you will run into severe interoperability problems when you
		1302	least expect it.
		1303
		1304	=over 4
		1305
		1306	=item (*)
		1307
		1308	I have been pressured multiple times by Brian Ingerson (one of the
		1309	authors of the YAML specification) to remove this paragraph, despite him
		1310	acknowledging that the actual incompatibilities exist. As I was personally
		1311	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1312	educate people about these issues, so others do not run into the same
		1313	problem again and again. After this, Brian called me a (quote)I<complete
		1314	and worthless idiot>(unquote).
		1315
		1316	In my opinion, instead of pressuring and insulting people who actually
		1317	clarify issues with YAML and the wrong statements of some of its
		1318	proponents, I would kindly suggest reading the JSON spec (which is not
		1319	that difficult or long) and finally make YAML compatible to it, and
		1320	educating users about the changes, instead of spreading lies about the
		1321	real compatibility for many I<years> and trying to silence people who
		1322	point out that it isn't true.
		1323
		1324	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1325	though the incompatibilities have been documented (and are known to Brian)
		1326	for many years and the spec makes explicit claims that YAML is a superset
		1327	of JSON. It would be so easy to fix, but apparently, bullying people and
		1328	corrupting userdata is so much easier.
		1329
		1330	=back
903		1331
904		1332
905	=head2 SPEED	1333	=head2 SPEED
906		1334
907	It seems that JSON::XS is surprisingly fast, as shown in the following	1335	It seems that JSON::XS is surprisingly fast, as shown in the following
908	tables. They have been generated with the help of the C<eg/bench> program	1336	tables. They have been generated with the help of the C<eg/bench> program
909	in the JSON::XS distribution, to make it easy to compare on your own	1337	in the JSON::XS distribution, to make it easy to compare on your own
910	system.	1338	system.
911		1339
912	First comes a comparison between various modules using a very short	1340	First comes a comparison between various modules using
913	single-line JSON string:	1341	a very short single-line JSON string (also available at
		1342	L<http://dist.schmorp.de/misc/json/short.json>).
914		1343
915	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1344	{"method": "handleMessage", "params": ["user1",
916	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1345	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1346	1, 0]}
917		1347
918	It shows the number of encodes/decodes per second (JSON::XS uses	1348	It shows the number of encodes/decodes per second (JSON::XS uses
919	the functional interface, while JSON::XS/2 uses the OO interface	1349	the functional interface, while JSON::XS/2 uses the OO interface
920	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1350	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
921	shrink). Higher is better:	1351	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1352	uses the from_json method). Higher is better:
922		1353
923	module \| encode \| decode \|	1354	module \| encode \| decode \|
924	-----------\|------------\|------------\|	1355	--------------\|------------\|------------\|
925	JSON 1.x \| 4990.842 \| 4088.813 \|	1356	JSON::DWIW/DS \| 86302.551 \| 102300.098 \|
926	JSON::DWIW \| 51653.990 \| 71575.154 \|	1357	JSON::DWIW/FJ \| 86302.551 \| 75983.768 \|
927	JSON::PC \| 65948.176 \| 74631.744 \|	1358	JSON::PP \| 15827.562 \| 6638.658 \|
928	JSON::PP \| 8931.652 \| 3817.168 \|	1359	JSON::Syck \| 63358.066 \| 47662.545 \|
929	JSON::Syck \| 24877.248 \| 27776.848 \|	1360	JSON::XS \| 511500.488 \| 511500.488 \|
930	JSON::XS \| 388361.481 \| 227951.304 \|	1361	JSON::XS/2 \| 291271.111 \| 388361.481 \|
931	JSON::XS/2 \| 227951.304 \| 218453.333 \|	1362	JSON::XS/3 \| 361577.931 \| 361577.931 \|
932	JSON::XS/3 \| 338250.323 \| 218453.333 \|	1363	Storable \| 66788.280 \| 265462.278 \|
933	Storable \| 16500.016 \| 135300.129 \|
934	-----------+------------+------------+	1364	--------------+------------+------------+
935		1365
936	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,	1366	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
937	about three times faster on decoding, and over forty times faster	1367	about five times faster on decoding, and over thirty to seventy times
938	than JSON, even with pretty-printing and key sorting. It also compares	1368	faster than JSON's pure perl implementation. It also compares favourably
939	favourably to Storable for small amounts of data.	1369	to Storable for small amounts of data.
940		1370
941	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1371	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
942	search API (http://nanoref.com/yahooapis/mgPdGg):	1372	search API (L<http://dist.schmorp.de/misc/json/long.json>).
943		1373
944	module \| encode \| decode \|	1374	module \| encode \| decode \|
945	-----------\|------------\|------------\|	1375	--------------\|------------\|------------\|
946	JSON 1.x \| 55.260 \| 34.971 \|	1376	JSON::DWIW/DS \| 1647.927 \| 2673.916 \|
947	JSON::DWIW \| 825.228 \| 1082.513 \|	1377	JSON::DWIW/FJ \| 1630.249 \| 2596.128 \|
948	JSON::PC \| 3571.444 \| 2394.829 \|
949	JSON::PP \| 210.987 \| 32.574 \|	1378	JSON::PP \| 400.640 \| 62.311 \|
950	JSON::Syck \| 552.551 \| 787.544 \|	1379	JSON::Syck \| 1481.040 \| 1524.869 \|
951	JSON::XS \| 5780.463 \| 4854.519 \|	1380	JSON::XS \| 20661.596 \| 9541.183 \|
952	JSON::XS/2 \| 3869.998 \| 4798.975 \|	1381	JSON::XS/2 \| 10683.403 \| 9416.938 \|
953	JSON::XS/3 \| 5862.880 \| 4798.975 \|	1382	JSON::XS/3 \| 20661.596 \| 9400.054 \|
954	Storable \| 4445.002 \| 5235.027 \|	1383	Storable \| 19765.806 \| 10000.725 \|
955	-----------+------------+------------+	1384	--------------+------------+------------+
956		1385
957	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1386	Again, JSON::XS leads by far (except for Storable which non-surprisingly
958	decodes faster).	1387	decodes a bit faster).
959		1388
960	On large strings containing lots of high Unicode characters, some modules	1389	On large strings containing lots of high Unicode characters, some modules
961	(such as JSON::PC) seem to decode faster than JSON::XS, but the result	1390	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
962	will be broken due to missing (or wrong) Unicode handling. Others refuse	1391	will be broken due to missing (or wrong) Unicode handling. Others refuse
963	to decode or encode properly, so it was impossible to prepare a fair	1392	to decode or encode properly, so it was impossible to prepare a fair
…		…
984		1413
985	Third, JSON::XS recurses using the C stack when decoding objects and	1414	Third, JSON::XS recurses using the C stack when decoding objects and
986	arrays. The C stack is a limited resource: for instance, on my amd64	1415	arrays. The C stack is a limited resource: for instance, on my amd64
987	machine with 8MB of stack size I can decode around 180k nested arrays but	1416	machine with 8MB of stack size I can decode around 180k nested arrays but
988	only 14k nested JSON objects (due to perl itself recursing deeply on croak	1417	only 14k nested JSON objects (due to perl itself recursing deeply on croak
989	to free the temporary). If that is exceeded, the program crashes. to be	1418	to free the temporary). If that is exceeded, the program crashes. To be
990	conservative, the default nesting limit is set to 512. If your process	1419	conservative, the default nesting limit is set to 512. If your process
991	has a smaller stack, you should adjust this setting accordingly with the	1420	has a smaller stack, you should adjust this setting accordingly with the
992	C<max_depth> method.	1421	C<max_depth> method.
993		1422
994	And last but least, something else could bomb you that I forgot to think	1423	Something else could bomb you, too, that I forgot to think of. In that
995	of. In that case, you get to keep the pieces. I am always open for hints,	1424	case, you get to keep the pieces. I am always open for hints, though...
996	though...	1425
		1426	Also keep in mind that JSON::XS might leak contents of your Perl data
		1427	structures in its error messages, so when you serialise sensitive
		1428	information you might want to make sure that exceptions thrown by JSON::XS
		1429	will not end up in front of untrusted eyes.
997		1430
998	If you are using JSON::XS to return packets to consumption	1431	If you are using JSON::XS to return packets to consumption
999	by JavaScript scripts in a browser you should have a look at	1432	by JavaScript scripts in a browser you should have a look at
1000	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether	1433	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
1001	you are vulnerable to some common attack vectors (which really are browser	1434	see whether you are vulnerable to some common attack vectors (which really
1002	design bugs, but it is still you who will have to deal with it, as major	1435	are browser design bugs, but it is still you who will have to deal with
1003	browser developers care only for features, not about doing security	1436	it, as major browser developers care only for features, not about getting
1004	right).	1437	security right).
1005		1438
1006		1439
1007	=head1 THREADS	1440	=head1 THREADS
1008		1441
1009	This module is I<not> guaranteed to be thread safe and there are no	1442	This module is I<not> guaranteed to be thread safe and there are no
1010	plans to change this until Perl gets thread support (as opposed to the	1443	plans to change this until Perl gets thread support (as opposed to the
1011	horribly slow so-called "threads" which are simply slow and bloated	1444	horribly slow so-called "threads" which are simply slow and bloated
1012	process simulations - use fork, its I<much> faster, cheaper, better).	1445	process simulations - use fork, it's I<much> faster, cheaper, better).
1013		1446
1014	(It might actually work, but you have been warned).	1447	(It might actually work, but you have been warned).
1015		1448
1016		1449
1017	=head1 BUGS	1450	=head1 BUGS
1018		1451
1019	While the goal of this module is to be correct, that unfortunately does	1452	While the goal of this module is to be correct, that unfortunately does
1020	not mean its bug-free, only that I think its design is bug-free. It is	1453	not mean it's bug-free, only that I think its design is bug-free. If you
1021	still relatively early in its development. If you keep reporting bugs they	1454	keep reporting bugs they will be fixed swiftly, though.
1022	will be fixed swiftly, though.
1023		1455
1024	Please refrain from using rt.cpan.org or any other bug reporting	1456	Please refrain from using rt.cpan.org or any other bug reporting
1025	service. I put the contact address into my modules for a reason.	1457	service. I put the contact address into my modules for a reason.
1026		1458
1027	=cut	1459	=cut
…		…
1047	"--" => sub { $_[0] = ${$_[0]} - 1 },	1479	"--" => sub { $_[0] = ${$_[0]} - 1 },
1048	fallback => 1;	1480	fallback => 1;
1049		1481
1050	1;	1482	1;
1051		1483
		1484	=head1 SEE ALSO
		1485
		1486	The F<json_xs> command line utility for quick experiments.
		1487
1052	=head1 AUTHOR	1488	=head1 AUTHOR
1053		1489
1054	Marc Lehmann <schmorp@schmorp.de>	1490	Marc Lehmann <schmorp@schmorp.de>
1055	http://home.schmorp.de/	1491	http://home.schmorp.de/
1056		1492

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Comparing JSON-XS/XS.pm (file contents): Revision 1.75 by root, Thu Nov 29 13:35:35 2007 UTC vs. Revision 1.138 by root, Wed Aug 1 19:04:41 2012 UTC

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Comparing JSON-XS/XS.pm (file contents):
Revision 1.75 by root, Thu Nov 29 13:35:35 2007 UTC vs.
Revision 1.138 by root, Wed Aug 1 19:04:41 2012 UTC