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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.77 by root, Tue Dec 4 10:37:42 2007 UTC vs.
Revision 1.141 by root, Fri Oct 25 19:53:08 2013 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	3	JSON::XS - JSON serialising/deserialising, done correctly and fast
		4
		5	=encoding utf-8
4		6
5	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ	7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
6	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)	8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
7		9
8	=head1 SYNOPSIS	10	=head1 SYNOPSIS
10	use JSON::XS;	12	use JSON::XS;
11		13
12	# exported functions, they croak on error	14	# exported functions, they croak on error
13	# and expect/generate UTF-8	15	# and expect/generate UTF-8
14		16
15	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
16	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
17		19
18	# OO-interface	20	# OO-interface
19		21
20	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
21	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
…		…
35	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
36	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.
37		39
38	Beginning with version 2.0 of the JSON module, when both JSON and	40	Beginning with version 2.0 of the JSON module, when both JSON and
39	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be	41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
40	overriden) with no overhead due to emulation (by inheritign constructor	42	overridden) with no overhead due to emulation (by inheriting constructor
41	and methods). If JSON::XS is not available, it will fall back to the	43	and methods). If JSON::XS is not available, it will fall back to the
42	compatible JSON::PP module as backend, so using JSON instead of JSON::XS	44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
43	gives you a portable JSON API that can be fast when you need and doesn't	45	gives you a portable JSON API that can be fast when you need and doesn't
44	require a C compiler when that is a problem.	46	require a C compiler when that is a problem.
45		47
…		…
47	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
48	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
49	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
50	reports for other reasons.	52	reports for other reasons.
51		53
52	See COMPARISON, below, for a comparison to some other JSON modules.
53
54	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
55	vice versa.	55	vice versa.
56		56
57	=head2 FEATURES	57	=head2 FEATURES
58		58
59	=over 4	59	=over 4
60		60
61	=item * correct Unicode handling	61	=item * correct Unicode handling
62		62
63	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
64	it does so.	64	so, and even documents what "correct" means.
65		65
66	=item * round-trip integrity	66	=item * round-trip integrity
67		67
68	When you serialise a perl data structure using only datatypes supported	68	When you serialise a perl data structure using only data types supported
69	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
70	(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
71	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.
72		73
73	=item * strict checking of JSON correctness	74	=item * strict checking of JSON correctness
74		75
75	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,
76	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
77	feature).	78	feature).
78		79
79	=item * fast	80	=item * fast
80		81
81	Compared to other JSON modules, this module compares favourably in terms	82	Compared to other JSON modules and other serialisers such as Storable,
82	of speed, too.	83	this module usually compares favourably in terms of speed, too.
83		84
84	=item * simple to use	85	=item * simple to use
85		86
86	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
87	interface.	88	oriented interface.
88		89
89	=item * reasonably versatile output formats	90	=item * reasonably versatile output formats
90		91
91	You can choose between the most compact guaranteed single-line format	92	You can choose between the most compact guaranteed-single-line format
92	possible (nice for simple line-based protocols), a pure-ascii format	93	possible (nice for simple line-based protocols), a pure-ASCII format
93	(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
94	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
95	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.
96		97
97	=back	98	=back
98		99
99	=cut	100	=cut
100		101
101	package JSON::XS;	102	package JSON::XS;
102		103
103	use strict;	104	use common::sense;
104		105
105	our $VERSION = '2.0';	106	our $VERSION = 2.34;
106	our @ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
107		108
108	our @EXPORT = qw(to_json from_json);	109	our @EXPORT = qw(encode_json decode_json);
109		110
110	use Exporter;	111	use Exporter;
111	use XSLoader;	112	use XSLoader;
112		113
113	=head1 FUNCTIONAL INTERFACE	114	=head1 FUNCTIONAL INTERFACE
…		…
115	The following convenience methods are provided by this module. They are	116	The following convenience methods are provided by this module. They are
116	exported by default:	117	exported by default:
117		118
118	=over 4	119	=over 4
119		120
120	=item $json_text = to_json $perl_scalar	121	=item $json_text = encode_json $perl_scalar
121		122
122	Converts the given Perl data structure to a UTF-8 encoded, binary string	123	Converts the given Perl data structure to a UTF-8 encoded, binary string
123	(that is, the string contains octets only). Croaks on error.	124	(that is, the string contains octets only). Croaks on error.
124		125
125	This function call is functionally identical to:	126	This function call is functionally identical to:
126		127
127	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	128	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
128		129
129	except being faster.	130	Except being faster.
130		131
131	=item $perl_scalar = from_json $json_text	132	=item $perl_scalar = decode_json $json_text
132		133
133	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries	134	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
134	to parse that as an UTF-8 encoded JSON text, returning the resulting	135	to parse that as an UTF-8 encoded JSON text, returning the resulting
135	reference. Croaks on error.	136	reference. Croaks on error.
136		137
137	This function call is functionally identical to:	138	This function call is functionally identical to:
138		139
139	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	140	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
140		141
141	except being faster.	142	Except being faster.
142		143
143	=item $is_boolean = JSON::XS::is_bool $scalar	144	=item $is_boolean = JSON::XS::is_bool $scalar
144		145
145	Returns true if the passed scalar represents either JSON::XS::true or	146	Returns true if the passed scalar represents either JSON::XS::true or
146	JSON::XS::false, two constants that act like C<1> and C<0>, respectively	147	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
…		…
164	This enables you to store Unicode characters as single characters in a	165	This enables you to store Unicode characters as single characters in a
165	Perl string - very natural.	166	Perl string - very natural.
166		167
167	=item 2. Perl does I<not> associate an encoding with your strings.	168	=item 2. Perl does I<not> associate an encoding with your strings.
168		169
169	Unless you force it to, e.g. when matching it against a regex, or printing	170	... until you force it to, e.g. when matching it against a regex, or
170	the scalar to a file, in which case Perl either interprets your string as	171	printing the scalar to a file, in which case Perl either interprets your
171	locale-encoded text, octets/binary, or as Unicode, depending on various	172	string as locale-encoded text, octets/binary, or as Unicode, depending
172	settings. In no case is an encoding stored together with your data, it is	173	on various settings. In no case is an encoding stored together with your
173	I<use> that decides encoding, not any magical metadata.	174	data, it is I<use> that decides encoding, not any magical meta data.
174		175
175	=item 3. The internal utf-8 flag has no meaning with regards to the	176	=item 3. The internal utf-8 flag has no meaning with regards to the
176	encoding of your string.	177	encoding of your string.
177		178
178	Just ignore that flag unless you debug a Perl bug, a module written in	179	Just ignore that flag unless you debug a Perl bug, a module written in
…		…
184		185
185	If you didn't know about that flag, just the better, pretend it doesn't	186	If you didn't know about that flag, just the better, pretend it doesn't
186	exist.	187	exist.
187		188
188	=item 4. A "Unicode String" is simply a string where each character can be	189	=item 4. A "Unicode String" is simply a string where each character can be
189	validly interpreted as a Unicode codepoint.	190	validly interpreted as a Unicode code point.
190		191
191	If you have UTF-8 encoded data, it is no longer a Unicode string, but a	192	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
192	Unicode string encoded in UTF-8, giving you a binary string.	193	Unicode string encoded in UTF-8, giving you a binary string.
193		194
194	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.	195	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
…		…
232		233
233	If C<$enable> is false, then the C<encode> method will not escape Unicode	234	If C<$enable> is false, then the C<encode> method will not escape Unicode
234	characters unless required by the JSON syntax or other flags. This results	235	characters unless required by the JSON syntax or other flags. This results
235	in a faster and more compact format.	236	in a faster and more compact format.
236		237
		238	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		239	document.
		240
237	The main use for this flag is to produce JSON texts that can be	241	The main use for this flag is to produce JSON texts that can be
238	transmitted over a 7-bit channel, as the encoded JSON texts will not	242	transmitted over a 7-bit channel, as the encoded JSON texts will not
239	contain any 8 bit characters.	243	contain any 8 bit characters.
240		244
241	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	245	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
…		…
252	will not be affected in any way by this flag, as C<decode> by default	256	will not be affected in any way by this flag, as C<decode> by default
253	expects Unicode, which is a strict superset of latin1.	257	expects Unicode, which is a strict superset of latin1.
254		258
255	If C<$enable> is false, then the C<encode> method will not escape Unicode	259	If C<$enable> is false, then the C<encode> method will not escape Unicode
256	characters unless required by the JSON syntax or other flags.	260	characters unless required by the JSON syntax or other flags.
		261
		262	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		263	document.
257		264
258	The main use for this flag is efficiently encoding binary data as JSON	265	The main use for this flag is efficiently encoding binary data as JSON
259	text, as most octets will not be escaped, resulting in a smaller encoded	266	text, as most octets will not be escaped, resulting in a smaller encoded
260	size. The disadvantage is that the resulting JSON text is encoded	267	size. The disadvantage is that the resulting JSON text is encoded
261	in latin1 (and must correctly be treated as such when storing and	268	in latin1 (and must correctly be treated as such when storing and
…		…
280		287
281	If C<$enable> is false, then the C<encode> method will return the JSON	288	If C<$enable> is false, then the C<encode> method will return the JSON
282	string as a (non-encoded) Unicode string, while C<decode> expects thus a	289	string as a (non-encoded) Unicode string, while C<decode> expects thus a
283	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	290	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
284	to be done yourself, e.g. using the Encode module.	291	to be done yourself, e.g. using the Encode module.
		292
		293	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		294	document.
285		295
286	Example, output UTF-16BE-encoded JSON:	296	Example, output UTF-16BE-encoded JSON:
287		297
288	use Encode;	298	use Encode;
289	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	299	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
412	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	422	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
413	by sorting their keys. This is adding a comparatively high overhead.	423	by sorting their keys. This is adding a comparatively high overhead.
414		424
415	If C<$enable> is false, then the C<encode> method will output key-value	425	If C<$enable> is false, then the C<encode> method will output key-value
416	pairs in the order Perl stores them (which will likely change between runs	426	pairs in the order Perl stores them (which will likely change between runs
417	of the same script).	427	of the same script, and can change even within the same run from 5.18
		428	onwards).
418		429
419	This option is useful if you want the same data structure to be encoded as	430	This option is useful if you want the same data structure to be encoded as
420	the same JSON text (given the same overall settings). If it is disabled,	431	the same JSON text (given the same overall settings). If it is disabled,
421	the same hash might be encoded differently even if contains the same data,	432	the same hash might be encoded differently even if contains the same data,
422	as key-value pairs have no inherent ordering in Perl.	433	as key-value pairs have no inherent ordering in Perl.
423		434
424	This setting has no effect when decoding JSON texts.	435	This setting has no effect when decoding JSON texts.
425		436
		437	This setting has currently no effect on tied hashes.
		438
426	=item $json = $json->allow_nonref ([$enable])	439	=item $json = $json->allow_nonref ([$enable])
427		440
428	=item $enabled = $json->get_allow_nonref	441	=item $enabled = $json->get_allow_nonref
429		442
430	If C<$enable> is true (or missing), then the C<encode> method can convert a	443	If C<$enable> is true (or missing), then the C<encode> method can convert a
…		…
440	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,	453	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
441	resulting in an invalid JSON text:	454	resulting in an invalid JSON text:
442		455
443	JSON::XS->new->allow_nonref->encode ("Hello, World!")	456	JSON::XS->new->allow_nonref->encode ("Hello, World!")
444	=> "Hello, World!"	457	=> "Hello, World!"
		458
		459	=item $json = $json->allow_unknown ([$enable])
		460
		461	=item $enabled = $json->get_allow_unknown
		462
		463	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		464	exception when it encounters values it cannot represent in JSON (for
		465	example, filehandles) but instead will encode a JSON C<null> value. Note
		466	that blessed objects are not included here and are handled separately by
		467	c<allow_nonref>.
		468
		469	If C<$enable> is false (the default), then C<encode> will throw an
		470	exception when it encounters anything it cannot encode as JSON.
		471
		472	This option does not affect C<decode> in any way, and it is recommended to
		473	leave it off unless you know your communications partner.
445		474
446	=item $json = $json->allow_blessed ([$enable])	475	=item $json = $json->allow_blessed ([$enable])
447		476
448	=item $enabled = $json->get_allow_blessed	477	=item $enabled = $json->get_allow_blessed
449		478
…		…
471	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>	500	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
472	returns other blessed objects, those will be handled in the same	501	returns other blessed objects, those will be handled in the same
473	way. C<TO_JSON> must take care of not causing an endless recursion cycle	502	way. C<TO_JSON> must take care of not causing an endless recursion cycle
474	(== crash) in this case. The name of C<TO_JSON> was chosen because other	503	(== crash) in this case. The name of C<TO_JSON> was chosen because other
475	methods called by the Perl core (== not by the user of the object) are	504	methods called by the Perl core (== not by the user of the object) are
476	usually in upper case letters and to avoid collisions with the C<to_json>	505	usually in upper case letters and to avoid collisions with any C<to_json>
477	function.	506	function or method.
478		507
479	This setting does not yet influence C<decode> in any way, but in the	508	This setting does not yet influence C<decode> in any way, but in the
480	future, global hooks might get installed that influence C<decode> and are	509	future, global hooks might get installed that influence C<decode> and are
481	enabled by this setting.	510	enabled by this setting.
482		511
…		…
590	=item $json = $json->max_depth ([$maximum_nesting_depth])	619	=item $json = $json->max_depth ([$maximum_nesting_depth])
591		620
592	=item $max_depth = $json->get_max_depth	621	=item $max_depth = $json->get_max_depth
593		622
594	Sets the maximum nesting level (default C<512>) accepted while encoding	623	Sets the maximum nesting level (default C<512>) accepted while encoding
595	or decoding. If the JSON text or Perl data structure has an equal or	624	or decoding. If a higher nesting level is detected in JSON text or a Perl
596	higher nesting level then this limit, then the encoder and decoder will	625	data structure, then the encoder and decoder will stop and croak at that
597	stop and croak at that point.	626	point.
598		627
599	Nesting level is defined by number of hash- or arrayrefs that the encoder	628	Nesting level is defined by number of hash- or arrayrefs that the encoder
600	needs to traverse to reach a given point or the number of C<{> or C<[>	629	needs to traverse to reach a given point or the number of C<{> or C<[>
601	characters without their matching closing parenthesis crossed to reach a	630	characters without their matching closing parenthesis crossed to reach a
602	given character in a string.	631	given character in a string.
603		632
604	Setting the maximum depth to one disallows any nesting, so that ensures	633	Setting the maximum depth to one disallows any nesting, so that ensures
605	that the object is only a single hash/object or array.	634	that the object is only a single hash/object or array.
606		635
607	The argument to C<max_depth> will be rounded up to the next highest power
608	of two. If no argument is given, the highest possible setting will be	636	If no argument is given, the highest possible setting will be used, which
609	used, which is rarely useful.	637	is rarely useful.
		638
		639	Note that nesting is implemented by recursion in C. The default value has
		640	been chosen to be as large as typical operating systems allow without
		641	crashing.
610		642
611	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	643	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
612		644
613	=item $json = $json->max_size ([$maximum_string_size])	645	=item $json = $json->max_size ([$maximum_string_size])
614		646
615	=item $max_size = $json->get_max_size	647	=item $max_size = $json->get_max_size
616		648
617	Set the maximum length a JSON text may have (in bytes) where decoding is	649	Set the maximum length a JSON text may have (in bytes) where decoding is
618	being attempted. The default is C<0>, meaning no limit. When C<decode>	650	being attempted. The default is C<0>, meaning no limit. When C<decode>
619	is called on a string longer then this number of characters it will not	651	is called on a string that is longer then this many bytes, it will not
620	attempt to decode the string but throw an exception. This setting has no	652	attempt to decode the string but throw an exception. This setting has no
621	effect on C<encode> (yet).	653	effect on C<encode> (yet).
622		654
623	The argument to C<max_size> will be rounded up to the next B<highest>	655	If no argument is given, the limit check will be deactivated (same as when
624	power of two (so may be more than requested). If no argument is given, the	656	C<0> is specified).
625	limit check will be deactivated (same as when C<0> is specified).
626		657
627	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	658	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
628		659
629	=item $json_text = $json->encode ($perl_scalar)	660	=item $json_text = $json->encode ($perl_scalar)
630		661
631	Converts the given Perl data structure (a simple scalar or a reference	662	Converts the given Perl value or data structure to its JSON
632	to a hash or array) to its JSON representation. Simple scalars will be	663	representation. Croaks on error.
633	converted into JSON string or number sequences, while references to arrays
634	become JSON arrays and references to hashes become JSON objects. Undefined
635	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
636	nor C<false> values will be generated.
637		664
638	=item $perl_scalar = $json->decode ($json_text)	665	=item $perl_scalar = $json->decode ($json_text)
639		666
640	The opposite of C<encode>: expects a JSON text and tries to parse it,	667	The opposite of C<encode>: expects a JSON text and tries to parse it,
641	returning the resulting simple scalar or reference. Croaks on error.	668	returning the resulting simple scalar or reference. Croaks on error.
642
643	JSON numbers and strings become simple Perl scalars. JSON arrays become
644	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
645	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
646		669
647	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)	670	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
648		671
649	This works like the C<decode> method, but instead of raising an exception	672	This works like the C<decode> method, but instead of raising an exception
650	when there is trailing garbage after the first JSON object, it will	673	when there is trailing garbage after the first JSON object, it will
…		…
659	=> ([], 3)	682	=> ([], 3)
660		683
661	=back	684	=back
662		685
663		686
		687	=head1 INCREMENTAL PARSING
		688
		689	In some cases, there is the need for incremental parsing of JSON
		690	texts. While this module always has to keep both JSON text and resulting
		691	Perl data structure in memory at one time, it does allow you to parse a
		692	JSON stream incrementally. It does so by accumulating text until it has
		693	a full JSON object, which it then can decode. This process is similar to
		694	using C<decode_prefix> to see if a full JSON object is available, but
		695	is much more efficient (and can be implemented with a minimum of method
		696	calls).
		697
		698	JSON::XS will only attempt to parse the JSON text once it is sure it
		699	has enough text to get a decisive result, using a very simple but
		700	truly incremental parser. This means that it sometimes won't stop as
		701	early as the full parser, for example, it doesn't detect mismatched
		702	parentheses. The only thing it guarantees is that it starts decoding as
		703	soon as a syntactically valid JSON text has been seen. This means you need
		704	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		705	parsing in the presence if syntax errors.
		706
		707	The following methods implement this incremental parser.
		708
		709	=over 4
		710
		711	=item [void, scalar or list context] = $json->incr_parse ([$string])
		712
		713	This is the central parsing function. It can both append new text and
		714	extract objects from the stream accumulated so far (both of these
		715	functions are optional).
		716
		717	If C<$string> is given, then this string is appended to the already
		718	existing JSON fragment stored in the C<$json> object.
		719
		720	After that, if the function is called in void context, it will simply
		721	return without doing anything further. This can be used to add more text
		722	in as many chunks as you want.
		723
		724	If the method is called in scalar context, then it will try to extract
		725	exactly I<one> JSON object. If that is successful, it will return this
		726	object, otherwise it will return C<undef>. If there is a parse error,
		727	this method will croak just as C<decode> would do (one can then use
		728	C<incr_skip> to skip the erroneous part). This is the most common way of
		729	using the method.
		730
		731	And finally, in list context, it will try to extract as many objects
		732	from the stream as it can find and return them, or the empty list
		733	otherwise. For this to work, there must be no separators between the JSON
		734	objects or arrays, instead they must be concatenated back-to-back. If
		735	an error occurs, an exception will be raised as in the scalar context
		736	case. Note that in this case, any previously-parsed JSON texts will be
		737	lost.
		738
		739	Example: Parse some JSON arrays/objects in a given string and return
		740	them.
		741
		742	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		743
		744	=item $lvalue_string = $json->incr_text
		745
		746	This method returns the currently stored JSON fragment as an lvalue, that
		747	is, you can manipulate it. This I<only> works when a preceding call to
		748	C<incr_parse> in I<scalar context> successfully returned an object. Under
		749	all other circumstances you must not call this function (I mean it.
		750	although in simple tests it might actually work, it I<will> fail under
		751	real world conditions). As a special exception, you can also call this
		752	method before having parsed anything.
		753
		754	This function is useful in two cases: a) finding the trailing text after a
		755	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		756	(such as commas).
		757
		758	=item $json->incr_skip
		759
		760	This will reset the state of the incremental parser and will remove
		761	the parsed text from the input buffer so far. This is useful after
		762	C<incr_parse> died, in which case the input buffer and incremental parser
		763	state is left unchanged, to skip the text parsed so far and to reset the
		764	parse state.
		765
		766	The difference to C<incr_reset> is that only text until the parse error
		767	occurred is removed.
		768
		769	=item $json->incr_reset
		770
		771	This completely resets the incremental parser, that is, after this call,
		772	it will be as if the parser had never parsed anything.
		773
		774	This is useful if you want to repeatedly parse JSON objects and want to
		775	ignore any trailing data, which means you have to reset the parser after
		776	each successful decode.
		777
		778	=back
		779
		780	=head2 LIMITATIONS
		781
		782	All options that affect decoding are supported, except
		783	C<allow_nonref>. The reason for this is that it cannot be made to
		784	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		785	them back to back and still decode them perfectly. This does not hold true
		786	for JSON numbers, however.
		787
		788	For example, is the string C<1> a single JSON number, or is it simply the
		789	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		790	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		791	takes the conservative route and disallows this case.
		792
		793	=head2 EXAMPLES
		794
		795	Some examples will make all this clearer. First, a simple example that
		796	works similarly to C<decode_prefix>: We want to decode the JSON object at
		797	the start of a string and identify the portion after the JSON object:
		798
		799	my $text = "[1,2,3] hello";
		800
		801	my $json = new JSON::XS;
		802
		803	my $obj = $json->incr_parse ($text)
		804	or die "expected JSON object or array at beginning of string";
		805
		806	my $tail = $json->incr_text;
		807	# $tail now contains " hello"
		808
		809	Easy, isn't it?
		810
		811	Now for a more complicated example: Imagine a hypothetical protocol where
		812	you read some requests from a TCP stream, and each request is a JSON
		813	array, without any separation between them (in fact, it is often useful to
		814	use newlines as "separators", as these get interpreted as whitespace at
		815	the start of the JSON text, which makes it possible to test said protocol
		816	with C<telnet>...).
		817
		818	Here is how you'd do it (it is trivial to write this in an event-based
		819	manner):
		820
		821	my $json = new JSON::XS;
		822
		823	# read some data from the socket
		824	while (sysread $socket, my $buf, 4096) {
		825
		826	# split and decode as many requests as possible
		827	for my $request ($json->incr_parse ($buf)) {
		828	# act on the $request
		829	}
		830	}
		831
		832	Another complicated example: Assume you have a string with JSON objects
		833	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		834	[3]>). To parse them, we have to skip the commas between the JSON texts,
		835	and here is where the lvalue-ness of C<incr_text> comes in useful:
		836
		837	my $text = "[1],[2], [3]";
		838	my $json = new JSON::XS;
		839
		840	# void context, so no parsing done
		841	$json->incr_parse ($text);
		842
		843	# now extract as many objects as possible. note the
		844	# use of scalar context so incr_text can be called.
		845	while (my $obj = $json->incr_parse) {
		846	# do something with $obj
		847
		848	# now skip the optional comma
		849	$json->incr_text =~ s/^ \s* , //x;
		850	}
		851
		852	Now lets go for a very complex example: Assume that you have a gigantic
		853	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		854	but you cannot load it into memory fully (this has actually happened in
		855	the real world :).
		856
		857	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		858	can still help you: You implement a (very simple) array parser and let
		859	JSON decode the array elements, which are all full JSON objects on their
		860	own (this wouldn't work if the array elements could be JSON numbers, for
		861	example):
		862
		863	my $json = new JSON::XS;
		864
		865	# open the monster
		866	open my $fh, "<bigfile.json"
		867	or die "bigfile: $!";
		868
		869	# first parse the initial "["
		870	for (;;) {
		871	sysread $fh, my $buf, 65536
		872	or die "read error: $!";
		873	$json->incr_parse ($buf); # void context, so no parsing
		874
		875	# Exit the loop once we found and removed(!) the initial "[".
		876	# In essence, we are (ab-)using the $json object as a simple scalar
		877	# we append data to.
		878	last if $json->incr_text =~ s/^ \s* \[ //x;
		879	}
		880
		881	# now we have the skipped the initial "[", so continue
		882	# parsing all the elements.
		883	for (;;) {
		884	# in this loop we read data until we got a single JSON object
		885	for (;;) {
		886	if (my $obj = $json->incr_parse) {
		887	# do something with $obj
		888	last;
		889	}
		890
		891	# add more data
		892	sysread $fh, my $buf, 65536
		893	or die "read error: $!";
		894	$json->incr_parse ($buf); # void context, so no parsing
		895	}
		896
		897	# in this loop we read data until we either found and parsed the
		898	# separating "," between elements, or the final "]"
		899	for (;;) {
		900	# first skip whitespace
		901	$json->incr_text =~ s/^\s*//;
		902
		903	# if we find "]", we are done
		904	if ($json->incr_text =~ s/^\]//) {
		905	print "finished.\n";
		906	exit;
		907	}
		908
		909	# if we find ",", we can continue with the next element
		910	if ($json->incr_text =~ s/^,//) {
		911	last;
		912	}
		913
		914	# if we find anything else, we have a parse error!
		915	if (length $json->incr_text) {
		916	die "parse error near ", $json->incr_text;
		917	}
		918
		919	# else add more data
		920	sysread $fh, my $buf, 65536
		921	or die "read error: $!";
		922	$json->incr_parse ($buf); # void context, so no parsing
		923	}
		924
		925	This is a complex example, but most of the complexity comes from the fact
		926	that we are trying to be correct (bear with me if I am wrong, I never ran
		927	the above example :).
		928
		929
		930
664	=head1 MAPPING	931	=head1 MAPPING
665		932
666	This section describes how JSON::XS maps Perl values to JSON values and	933	This section describes how JSON::XS maps Perl values to JSON values and
667	vice versa. These mappings are designed to "do the right thing" in most	934	vice versa. These mappings are designed to "do the right thing" in most
668	circumstances automatically, preserving round-tripping characteristics	935	circumstances automatically, preserving round-tripping characteristics
…		…
696		963
697	A JSON number becomes either an integer, numeric (floating point) or	964	A JSON number becomes either an integer, numeric (floating point) or
698	string scalar in perl, depending on its range and any fractional parts. On	965	string scalar in perl, depending on its range and any fractional parts. On
699	the Perl level, there is no difference between those as Perl handles all	966	the Perl level, there is no difference between those as Perl handles all
700	the conversion details, but an integer may take slightly less memory and	967	the conversion details, but an integer may take slightly less memory and
701	might represent more values exactly than (floating point) numbers.	968	might represent more values exactly than floating point numbers.
702		969
703	If the number consists of digits only, JSON::XS will try to represent	970	If the number consists of digits only, JSON::XS will try to represent
704	it as an integer value. If that fails, it will try to represent it as	971	it as an integer value. If that fails, it will try to represent it as
705	a numeric (floating point) value if that is possible without loss of	972	a numeric (floating point) value if that is possible without loss of
706	precision. Otherwise it will preserve the number as a string value.	973	precision. Otherwise it will preserve the number as a string value (in
		974	which case you lose roundtripping ability, as the JSON number will be
		975	re-encoded to a JSON string).
707		976
708	Numbers containing a fractional or exponential part will always be	977	Numbers containing a fractional or exponential part will always be
709	represented as numeric (floating point) values, possibly at a loss of	978	represented as numeric (floating point) values, possibly at a loss of
710	precision.	979	precision (in which case you might lose perfect roundtripping ability, but
		980	the JSON number will still be re-encoded as a JSON number).
711		981
712	This might create round-tripping problems as numbers might become strings,	982	Note that precision is not accuracy - binary floating point values cannot
713	but as Perl is typeless there is no other way to do it.	983	represent most decimal fractions exactly, and when converting from and to
		984	floating point, JSON::XS only guarantees precision up to but not including
		985	the least significant bit.
714		986
715	=item true, false	987	=item true, false
716		988
717	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	989	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
718	respectively. They are overloaded to act almost exactly like the numbers	990	respectively. They are overloaded to act almost exactly like the numbers
…		…
755	Other unblessed references are generally not allowed and will cause an	1027	Other unblessed references are generally not allowed and will cause an
756	exception to be thrown, except for references to the integers C<0> and	1028	exception to be thrown, except for references to the integers C<0> and
757	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	1029	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
758	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.	1030	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
759		1031
760	to_json [\0,JSON::XS::true] # yields [false,true]	1032	encode_json [\0, JSON::XS::true] # yields [false,true]
761		1033
762	=item JSON::XS::true, JSON::XS::false	1034	=item JSON::XS::true, JSON::XS::false
763		1035
764	These special values become JSON true and JSON false values,	1036	These special values become JSON true and JSON false values,
765	respectively. You can also use C<\1> and C<\0> directly if you want.	1037	respectively. You can also use C<\1> and C<\0> directly if you want.
766		1038
767	=item blessed objects	1039	=item blessed objects
768		1040
769	Blessed objects are not allowed. JSON::XS currently tries to encode their	1041	Blessed objects are not directly representable in JSON. See the
770	underlying representation (hash- or arrayref), but this behaviour might	1042	C<allow_blessed> and C<convert_blessed> methods on various options on
771	change in future versions.	1043	how to deal with this: basically, you can choose between throwing an
		1044	exception, encoding the reference as if it weren't blessed, or provide
		1045	your own serialiser method.
772		1046
773	=item simple scalars	1047	=item simple scalars
774		1048
775	Simple Perl scalars (any scalar that is not a reference) are the most	1049	Simple Perl scalars (any scalar that is not a reference) are the most
776	difficult objects to encode: JSON::XS will encode undefined scalars as	1050	difficult objects to encode: JSON::XS will encode undefined scalars as
777	JSON null value, scalars that have last been used in a string context	1051	JSON C<null> values, scalars that have last been used in a string context
778	before encoding as JSON strings and anything else as number value:	1052	before encoding as JSON strings, and anything else as number value:
779		1053
780	# dump as number	1054	# dump as number
781	to_json [2] # yields [2]	1055	encode_json [2] # yields [2]
782	to_json [-3.0e17] # yields [-3e+17]	1056	encode_json [-3.0e17] # yields [-3e+17]
783	my $value = 5; to_json [$value] # yields [5]	1057	my $value = 5; encode_json [$value] # yields [5]
784		1058
785	# used as string, so dump as string	1059	# used as string, so dump as string
786	print $value;	1060	print $value;
787	to_json [$value] # yields ["5"]	1061	encode_json [$value] # yields ["5"]
788		1062
789	# undef becomes null	1063	# undef becomes null
790	to_json [undef] # yields [null]	1064	encode_json [undef] # yields [null]
791		1065
792	You can force the type to be a JSON string by stringifying it:	1066	You can force the type to be a JSON string by stringifying it:
793		1067
794	my $x = 3.1; # some variable containing a number	1068	my $x = 3.1; # some variable containing a number
795	"$x"; # stringified	1069	"$x"; # stringified
…		…
801	my $x = "3"; # some variable containing a string	1075	my $x = "3"; # some variable containing a string
802	$x += 0; # numify it, ensuring it will be dumped as a number	1076	$x += 0; # numify it, ensuring it will be dumped as a number
803	$x *= 1; # same thing, the choice is yours.	1077	$x *= 1; # same thing, the choice is yours.
804		1078
805	You can not currently force the type in other, less obscure, ways. Tell me	1079	You can not currently force the type in other, less obscure, ways. Tell me
806	if you need this capability.	1080	if you need this capability (but don't forget to explain why it's needed
		1081	:).
		1082
		1083	Note that numerical precision has the same meaning as under Perl (so
		1084	binary to decimal conversion follows the same rules as in Perl, which
		1085	can differ to other languages). Also, your perl interpreter might expose
		1086	extensions to the floating point numbers of your platform, such as
		1087	infinities or NaN's - these cannot be represented in JSON, and it is an
		1088	error to pass those in.
807		1089
808	=back	1090	=back
809		1091
810		1092
811	=head1 COMPARISON	1093	=head1 ENCODING/CODESET FLAG NOTES
812		1094
813	As already mentioned, this module was created because none of the existing	1095	The interested reader might have seen a number of flags that signify
814	JSON modules could be made to work correctly. First I will describe the	1096	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
815	problems (or pleasures) I encountered with various existing JSON modules,	1097	some confusion on what these do, so here is a short comparison:
816	followed by some benchmark values. JSON::XS was designed not to suffer	1098
817	from any of these problems or limitations.	1099	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1100	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1101	control whether C<encode> escapes character values outside their respective
		1102	codeset range. Neither of these flags conflict with each other, although
		1103	some combinations make less sense than others.
		1104
		1105	Care has been taken to make all flags symmetrical with respect to
		1106	C<encode> and C<decode>, that is, texts encoded with any combination of
		1107	these flag values will be correctly decoded when the same flags are used
		1108	- in general, if you use different flag settings while encoding vs. when
		1109	decoding you likely have a bug somewhere.
		1110
		1111	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1112	simply an abstract set of character-codepoint pairs, while an encoding
		1113	takes those codepoint numbers and I<encodes> them, in our case into
		1114	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1115	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1116	the same time, which can be confusing.
818		1117
819	=over 4	1118	=over 4
820		1119
821	=item JSON 1.07	1120	=item C<utf8> flag disabled
822		1121
823	Slow (but very portable, as it is written in pure Perl).	1122	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1123	and expect Unicode strings, that is, characters with high ordinal Unicode
		1124	values (> 255) will be encoded as such characters, and likewise such
		1125	characters are decoded as-is, no changes to them will be done, except
		1126	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1127	respectively (to Perl, these are the same thing in strings unless you do
		1128	funny/weird/dumb stuff).
824		1129
825	Undocumented/buggy Unicode handling (how JSON handles Unicode values is	1130	This is useful when you want to do the encoding yourself (e.g. when you
826	undocumented. One can get far by feeding it Unicode strings and doing	1131	want to have UTF-16 encoded JSON texts) or when some other layer does
827	en-/decoding oneself, but Unicode escapes are not working properly).	1132	the encoding for you (for example, when printing to a terminal using a
		1133	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1134	to UTF-8 encode your data first and have Perl encode it another time).
828		1135
829	No round-tripping (strings get clobbered if they look like numbers, e.g.	1136	=item C<utf8> flag enabled
830	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
831	decode into the number 2.
832		1137
833	=item JSON::PC 0.01	1138	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1139	characters using the corresponding UTF-8 multi-byte sequence, and will
		1140	expect your input strings to be encoded as UTF-8, that is, no "character"
		1141	of the input string must have any value > 255, as UTF-8 does not allow
		1142	that.
834		1143
835	Very fast.	1144	The C<utf8> flag therefore switches between two modes: disabled means you
		1145	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1146	octet/binary string in Perl.
836		1147
837	Undocumented/buggy Unicode handling.	1148	=item C<latin1> or C<ascii> flags enabled
838		1149
839	No round-tripping.	1150	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1151	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1152	characters as specified by the C<utf8> flag.
840		1153
841	Has problems handling many Perl values (e.g. regex results and other magic	1154	If C<utf8> is disabled, then the result is also correctly encoded in those
842	values will make it croak).	1155	character sets (as both are proper subsets of Unicode, meaning that a
		1156	Unicode string with all character values < 256 is the same thing as a
		1157	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1158	the same thing as an ASCII string in Perl).
843		1159
844	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1160	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
845	which is not a valid JSON text.	1161	regardless of these flags, just some more characters will be escaped using
		1162	C<\uXXXX> then before.
846		1163
847	Unmaintained (maintainer unresponsive for many months, bugs are not	1164	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
848	getting fixed).	1165	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1166	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1167	a subset of Unicode), while ASCII is.
849		1168
850	=item JSON::Syck 0.21	1169	Surprisingly, C<decode> will ignore these flags and so treat all input
		1170	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1171	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1172	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
851		1173
852	Very buggy (often crashes).	1174	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1175	they only govern when the JSON output engine escapes a character or not.
853		1176
854	Very inflexible (no human-readable format supported, format pretty much	1177	The main use for C<latin1> is to relatively efficiently store binary data
855	undocumented. I need at least a format for easy reading by humans and a	1178	as JSON, at the expense of breaking compatibility with most JSON decoders.
856	single-line compact format for use in a protocol, and preferably a way to
857	generate ASCII-only JSON texts).
858		1179
859	Completely broken (and confusingly documented) Unicode handling (Unicode	1180	The main use for C<ascii> is to force the output to not contain characters
860	escapes are not working properly, you need to set ImplicitUnicode to	1181	with values > 127, which means you can interpret the resulting string
861	I<different> values on en- and decoding to get symmetric behaviour).	1182	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
862		1183	8-bit-encoding, and still get the same data structure back. This is useful
863	No round-tripping (simple cases work, but this depends on whether the scalar	1184	when your channel for JSON transfer is not 8-bit clean or the encoding
864	value was used in a numeric context or not).	1185	might be mangled in between (e.g. in mail), and works because ASCII is a
865		1186	proper subset of most 8-bit and multibyte encodings in use in the world.
866	Dumping hashes may skip hash values depending on iterator state.
867
868	Unmaintained (maintainer unresponsive for many months, bugs are not
869	getting fixed).
870
871	Does not check input for validity (i.e. will accept non-JSON input and
872	return "something" instead of raising an exception. This is a security
873	issue: imagine two banks transferring money between each other using
874	JSON. One bank might parse a given non-JSON request and deduct money,
875	while the other might reject the transaction with a syntax error. While a
876	good protocol will at least recover, that is extra unnecessary work and
877	the transaction will still not succeed).
878
879	=item JSON::DWIW 0.04
880
881	Very fast. Very natural. Very nice.
882
883	Undocumented Unicode handling (but the best of the pack. Unicode escapes
884	still don't get parsed properly).
885
886	Very inflexible.
887
888	No round-tripping.
889
890	Does not generate valid JSON texts (key strings are often unquoted, empty keys
891	result in nothing being output)
892
893	Does not check input for validity.
894		1187
895	=back	1188	=back
896		1189
897		1190
		1191	=head2 JSON and ECMAscript
		1192
		1193	JSON syntax is based on how literals are represented in javascript (the
		1194	not-standardised predecessor of ECMAscript) which is presumably why it is
		1195	called "JavaScript Object Notation".
		1196
		1197	However, JSON is not a subset (and also not a superset of course) of
		1198	ECMAscript (the standard) or javascript (whatever browsers actually
		1199	implement).
		1200
		1201	If you want to use javascript's C<eval> function to "parse" JSON, you
		1202	might run into parse errors for valid JSON texts, or the resulting data
		1203	structure might not be queryable:
		1204
		1205	One of the problems is that U+2028 and U+2029 are valid characters inside
		1206	JSON strings, but are not allowed in ECMAscript string literals, so the
		1207	following Perl fragment will not output something that can be guaranteed
		1208	to be parsable by javascript's C<eval>:
		1209
		1210	use JSON::XS;
		1211
		1212	print encode_json [chr 0x2028];
		1213
		1214	The right fix for this is to use a proper JSON parser in your javascript
		1215	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1216	F<json2.js> parser).
		1217
		1218	If this is not an option, you can, as a stop-gap measure, simply encode to
		1219	ASCII-only JSON:
		1220
		1221	use JSON::XS;
		1222
		1223	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1224
		1225	Note that this will enlarge the resulting JSON text quite a bit if you
		1226	have many non-ASCII characters. You might be tempted to run some regexes
		1227	to only escape U+2028 and U+2029, e.g.:
		1228
		1229	# DO NOT USE THIS!
		1230	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1231	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1232	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1233	print $json;
		1234
		1235	Note that I<this is a bad idea>: the above only works for U+2028 and
		1236	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1237	javascript implementations, however, have issues with other characters as
		1238	well - using C<eval> naively simply I<will> cause problems.
		1239
		1240	Another problem is that some javascript implementations reserve
		1241	some property names for their own purposes (which probably makes
		1242	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1243	C<__proto__> property name for its own purposes.
		1244
		1245	If that is a problem, you could parse try to filter the resulting JSON
		1246	output for these property strings, e.g.:
		1247
		1248	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1249
		1250	This works because C<__proto__> is not valid outside of strings, so every
		1251	occurrence of C<"__proto__"\s*:> must be a string used as property name.
		1252
		1253	If you know of other incompatibilities, please let me know.
		1254
		1255
898	=head2 JSON and YAML	1256	=head2 JSON and YAML
899		1257
900	You often hear that JSON is a subset (or a close subset) of YAML. This is,	1258	You often hear that JSON is a subset of YAML. This is, however, a mass
901	however, a mass hysteria and very far from the truth. In general, there is	1259	hysteria(*) and very far from the truth (as of the time of this writing),
902	no way to configure JSON::XS to output a data structure as valid YAML.	1260	so let me state it clearly: I<in general, there is no way to configure
		1261	JSON::XS to output a data structure as valid YAML> that works in all
		1262	cases.
903		1263
904	If you really must use JSON::XS to generate YAML, you should use this	1264	If you really must use JSON::XS to generate YAML, you should use this
905	algorithm (subject to change in future versions):	1265	algorithm (subject to change in future versions):
906		1266
907	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1267	my $to_yaml = JSON::XS->new->utf8->space_after (1);
908	my $yaml = $to_yaml->encode ($ref) . "\n";	1268	my $yaml = $to_yaml->encode ($ref) . "\n";
909		1269
910	This will usually generate JSON texts that also parse as valid	1270	This will I<usually> generate JSON texts that also parse as valid
911	YAML. Please note that YAML has hardcoded limits on (simple) object key	1271	YAML. Please note that YAML has hardcoded limits on (simple) object key
912	lengths that JSON doesn't have, so you should make sure that your hash	1272	lengths that JSON doesn't have and also has different and incompatible
		1273	unicode character escape syntax, so you should make sure that your hash
913	keys are noticeably shorter than the 1024 characters YAML allows.	1274	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1275	and that you do not have characters with codepoint values outside the
		1276	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1277	sequences in strings (which JSON::XS does not I<currently> generate, but
		1278	other JSON generators might).
914		1279
915	There might be other incompatibilities that I am not aware of. In general	1280	There might be other incompatibilities that I am not aware of (or the YAML
		1281	specification has been changed yet again - it does so quite often). In
916	you should not try to generate YAML with a JSON generator or vice versa,	1282	general you should not try to generate YAML with a JSON generator or vice
917	or try to parse JSON with a YAML parser or vice versa: chances are high	1283	versa, or try to parse JSON with a YAML parser or vice versa: chances are
918	that you will run into severe interoperability problems.	1284	high that you will run into severe interoperability problems when you
		1285	least expect it.
		1286
		1287	=over 4
		1288
		1289	=item (*)
		1290
		1291	I have been pressured multiple times by Brian Ingerson (one of the
		1292	authors of the YAML specification) to remove this paragraph, despite him
		1293	acknowledging that the actual incompatibilities exist. As I was personally
		1294	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1295	educate people about these issues, so others do not run into the same
		1296	problem again and again. After this, Brian called me a (quote)I<complete
		1297	and worthless idiot>(unquote).
		1298
		1299	In my opinion, instead of pressuring and insulting people who actually
		1300	clarify issues with YAML and the wrong statements of some of its
		1301	proponents, I would kindly suggest reading the JSON spec (which is not
		1302	that difficult or long) and finally make YAML compatible to it, and
		1303	educating users about the changes, instead of spreading lies about the
		1304	real compatibility for many I<years> and trying to silence people who
		1305	point out that it isn't true.
		1306
		1307	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1308	though the incompatibilities have been documented (and are known to Brian)
		1309	for many years and the spec makes explicit claims that YAML is a superset
		1310	of JSON. It would be so easy to fix, but apparently, bullying people and
		1311	corrupting userdata is so much easier.
		1312
		1313	=back
919		1314
920		1315
921	=head2 SPEED	1316	=head2 SPEED
922		1317
923	It seems that JSON::XS is surprisingly fast, as shown in the following	1318	It seems that JSON::XS is surprisingly fast, as shown in the following
924	tables. They have been generated with the help of the C<eg/bench> program	1319	tables. They have been generated with the help of the C<eg/bench> program
925	in the JSON::XS distribution, to make it easy to compare on your own	1320	in the JSON::XS distribution, to make it easy to compare on your own
926	system.	1321	system.
927		1322
928	First comes a comparison between various modules using a very short	1323	First comes a comparison between various modules using
929	single-line JSON string:	1324	a very short single-line JSON string (also available at
		1325	L<http://dist.schmorp.de/misc/json/short.json>).
930		1326
931	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1327	{"method": "handleMessage", "params": ["user1",
932	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1328	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1329	1, 0]}
933		1330
934	It shows the number of encodes/decodes per second (JSON::XS uses	1331	It shows the number of encodes/decodes per second (JSON::XS uses
935	the functional interface, while JSON::XS/2 uses the OO interface	1332	the functional interface, while JSON::XS/2 uses the OO interface
936	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1333	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
937	shrink). Higher is better:	1334	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1335	uses the from_json method). Higher is better:
938		1336
939	module \| encode \| decode \|	1337	module \| encode \| decode \|
940	-----------\|------------\|------------\|	1338	--------------\|------------\|------------\|
941	JSON 1.x \| 4990.842 \| 4088.813 \|	1339	JSON::DWIW/DS \| 86302.551 \| 102300.098 \|
942	JSON::DWIW \| 51653.990 \| 71575.154 \|	1340	JSON::DWIW/FJ \| 86302.551 \| 75983.768 \|
943	JSON::PC \| 65948.176 \| 74631.744 \|	1341	JSON::PP \| 15827.562 \| 6638.658 \|
944	JSON::PP \| 8931.652 \| 3817.168 \|	1342	JSON::Syck \| 63358.066 \| 47662.545 \|
945	JSON::Syck \| 24877.248 \| 27776.848 \|	1343	JSON::XS \| 511500.488 \| 511500.488 \|
946	JSON::XS \| 388361.481 \| 227951.304 \|	1344	JSON::XS/2 \| 291271.111 \| 388361.481 \|
947	JSON::XS/2 \| 227951.304 \| 218453.333 \|	1345	JSON::XS/3 \| 361577.931 \| 361577.931 \|
948	JSON::XS/3 \| 338250.323 \| 218453.333 \|	1346	Storable \| 66788.280 \| 265462.278 \|
949	Storable \| 16500.016 \| 135300.129 \|
950	-----------+------------+------------+	1347	--------------+------------+------------+
951		1348
952	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,	1349	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
953	about three times faster on decoding, and over forty times faster	1350	about five times faster on decoding, and over thirty to seventy times
954	than JSON, even with pretty-printing and key sorting. It also compares	1351	faster than JSON's pure perl implementation. It also compares favourably
955	favourably to Storable for small amounts of data.	1352	to Storable for small amounts of data.
956		1353
957	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1354	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
958	search API (http://nanoref.com/yahooapis/mgPdGg):	1355	search API (L<http://dist.schmorp.de/misc/json/long.json>).
959		1356
960	module \| encode \| decode \|	1357	module \| encode \| decode \|
961	-----------\|------------\|------------\|	1358	--------------\|------------\|------------\|
962	JSON 1.x \| 55.260 \| 34.971 \|	1359	JSON::DWIW/DS \| 1647.927 \| 2673.916 \|
963	JSON::DWIW \| 825.228 \| 1082.513 \|	1360	JSON::DWIW/FJ \| 1630.249 \| 2596.128 \|
964	JSON::PC \| 3571.444 \| 2394.829 \|
965	JSON::PP \| 210.987 \| 32.574 \|	1361	JSON::PP \| 400.640 \| 62.311 \|
966	JSON::Syck \| 552.551 \| 787.544 \|	1362	JSON::Syck \| 1481.040 \| 1524.869 \|
967	JSON::XS \| 5780.463 \| 4854.519 \|	1363	JSON::XS \| 20661.596 \| 9541.183 \|
968	JSON::XS/2 \| 3869.998 \| 4798.975 \|	1364	JSON::XS/2 \| 10683.403 \| 9416.938 \|
969	JSON::XS/3 \| 5862.880 \| 4798.975 \|	1365	JSON::XS/3 \| 20661.596 \| 9400.054 \|
970	Storable \| 4445.002 \| 5235.027 \|	1366	Storable \| 19765.806 \| 10000.725 \|
971	-----------+------------+------------+	1367	--------------+------------+------------+
972		1368
973	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1369	Again, JSON::XS leads by far (except for Storable which non-surprisingly
974	decodes faster).	1370	decodes a bit faster).
975		1371
976	On large strings containing lots of high Unicode characters, some modules	1372	On large strings containing lots of high Unicode characters, some modules
977	(such as JSON::PC) seem to decode faster than JSON::XS, but the result	1373	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
978	will be broken due to missing (or wrong) Unicode handling. Others refuse	1374	will be broken due to missing (or wrong) Unicode handling. Others refuse
979	to decode or encode properly, so it was impossible to prepare a fair	1375	to decode or encode properly, so it was impossible to prepare a fair
…		…
1000		1396
1001	Third, JSON::XS recurses using the C stack when decoding objects and	1397	Third, JSON::XS recurses using the C stack when decoding objects and
1002	arrays. The C stack is a limited resource: for instance, on my amd64	1398	arrays. The C stack is a limited resource: for instance, on my amd64
1003	machine with 8MB of stack size I can decode around 180k nested arrays but	1399	machine with 8MB of stack size I can decode around 180k nested arrays but
1004	only 14k nested JSON objects (due to perl itself recursing deeply on croak	1400	only 14k nested JSON objects (due to perl itself recursing deeply on croak
1005	to free the temporary). If that is exceeded, the program crashes. to be	1401	to free the temporary). If that is exceeded, the program crashes. To be
1006	conservative, the default nesting limit is set to 512. If your process	1402	conservative, the default nesting limit is set to 512. If your process
1007	has a smaller stack, you should adjust this setting accordingly with the	1403	has a smaller stack, you should adjust this setting accordingly with the
1008	C<max_depth> method.	1404	C<max_depth> method.
1009		1405
1010	And last but least, something else could bomb you that I forgot to think	1406	Something else could bomb you, too, that I forgot to think of. In that
1011	of. In that case, you get to keep the pieces. I am always open for hints,	1407	case, you get to keep the pieces. I am always open for hints, though...
1012	though...	1408
		1409	Also keep in mind that JSON::XS might leak contents of your Perl data
		1410	structures in its error messages, so when you serialise sensitive
		1411	information you might want to make sure that exceptions thrown by JSON::XS
		1412	will not end up in front of untrusted eyes.
1013		1413
1014	If you are using JSON::XS to return packets to consumption	1414	If you are using JSON::XS to return packets to consumption
1015	by JavaScript scripts in a browser you should have a look at	1415	by JavaScript scripts in a browser you should have a look at
1016	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether	1416	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
1017	you are vulnerable to some common attack vectors (which really are browser	1417	see whether you are vulnerable to some common attack vectors (which really
1018	design bugs, but it is still you who will have to deal with it, as major	1418	are browser design bugs, but it is still you who will have to deal with
1019	browser developers care only for features, not about doing security	1419	it, as major browser developers care only for features, not about getting
1020	right).	1420	security right).
1021		1421
1022		1422
1023	=head1 THREADS	1423	=head1 THREADS
1024		1424
1025	This module is I<not> guaranteed to be thread safe and there are no	1425	This module is I<not> guaranteed to be thread safe and there are no
1026	plans to change this until Perl gets thread support (as opposed to the	1426	plans to change this until Perl gets thread support (as opposed to the
1027	horribly slow so-called "threads" which are simply slow and bloated	1427	horribly slow so-called "threads" which are simply slow and bloated
1028	process simulations - use fork, its I<much> faster, cheaper, better).	1428	process simulations - use fork, it's I<much> faster, cheaper, better).
1029		1429
1030	(It might actually work, but you have been warned).	1430	(It might actually work, but you have been warned).
1031		1431
1032		1432
		1433	=head1 THE PERILS OF SETLOCALE
		1434
		1435	Sometimes people avoid the Perl locale support and directly call the
		1436	system's setlocale function with C<LC_ALL>.
		1437
		1438	This breaks both perl and modules such as JSON::XS, as stringification of
		1439	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1440	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1441	perl to stringify numbers).
		1442
		1443	The solution is simple: don't call C<setlocale>, or use it for only those
		1444	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1445
		1446	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1447	actually needs it (avoiding stringification of numbers), and restore it
		1448	afterwards.
		1449
		1450
1033	=head1 BUGS	1451	=head1 BUGS
1034		1452
1035	While the goal of this module is to be correct, that unfortunately does	1453	While the goal of this module is to be correct, that unfortunately does
1036	not mean its bug-free, only that I think its design is bug-free. It is	1454	not mean it's bug-free, only that I think its design is bug-free. If you
1037	still relatively early in its development. If you keep reporting bugs they	1455	keep reporting bugs they will be fixed swiftly, though.
1038	will be fixed swiftly, though.
1039		1456
1040	Please refrain from using rt.cpan.org or any other bug reporting	1457	Please refrain from using rt.cpan.org or any other bug reporting
1041	service. I put the contact address into my modules for a reason.	1458	service. I put the contact address into my modules for a reason.
1042		1459
1043	=cut	1460	=cut
…		…
1063	"--" => sub { $_[0] = ${$_[0]} - 1 },	1480	"--" => sub { $_[0] = ${$_[0]} - 1 },
1064	fallback => 1;	1481	fallback => 1;
1065		1482
1066	1;	1483	1;
1067		1484
		1485	=head1 SEE ALSO
		1486
		1487	The F<json_xs> command line utility for quick experiments.
		1488
1068	=head1 AUTHOR	1489	=head1 AUTHOR
1069		1490
1070	Marc Lehmann <schmorp@schmorp.de>	1491	Marc Lehmann <schmorp@schmorp.de>
1071	http://home.schmorp.de/	1492	http://home.schmorp.de/
1072		1493

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Comparing JSON-XS/XS.pm (file contents): Revision 1.77 by root, Tue Dec 4 10:37:42 2007 UTC vs. Revision 1.141 by root, Fri Oct 25 19:53:08 2013 UTC

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Comparing JSON-XS/XS.pm (file contents):
Revision 1.77 by root, Tue Dec 4 10:37:42 2007 UTC vs.
Revision 1.141 by root, Fri Oct 25 19:53:08 2013 UTC