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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.82 by root, Sun Dec 30 21:24:57 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
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 = '2.01';	106	our $VERSION = 2.34;
106	our @ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
107		108
108	our @EXPORT = qw(encode_json decode_json to_json from_json);	109	our @EXPORT = qw(encode_json decode_json);
109
110	sub to_json($) {
111	require Carp;
112	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");
113	}
114
115	sub from_json($) {
116	require Carp;
117	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");
118	}
119		110
120	use Exporter;	111	use Exporter;
121	use XSLoader;	112	use XSLoader;
122		113
123	=head1 FUNCTIONAL INTERFACE	114	=head1 FUNCTIONAL INTERFACE
…		…
134		125
135	This function call is functionally identical to:	126	This function call is functionally identical to:
136		127
137	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	128	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
138		129
139	except being faster.	130	Except being faster.
140		131
141	=item $perl_scalar = decode_json $json_text	132	=item $perl_scalar = decode_json $json_text
142		133
143	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries	134	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
144	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
…		…
146		137
147	This function call is functionally identical to:	138	This function call is functionally identical to:
148		139
149	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	140	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
150		141
151	except being faster.	142	Except being faster.
152		143
153	=item $is_boolean = JSON::XS::is_bool $scalar	144	=item $is_boolean = JSON::XS::is_bool $scalar
154		145
155	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
156	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
…		…
174	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
175	Perl string - very natural.	166	Perl string - very natural.
176		167
177	=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.
178		169
179	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
180	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
181	locale-encoded text, octets/binary, or as Unicode, depending on various	172	string as locale-encoded text, octets/binary, or as Unicode, depending
182	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
183	I<use> that decides encoding, not any magical metadata.	174	data, it is I<use> that decides encoding, not any magical meta data.
184		175
185	=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
186	encoding of your string.	177	encoding of your string.
187		178
188	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
…		…
194		185
195	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
196	exist.	187	exist.
197		188
198	=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
199	validly interpreted as a Unicode codepoint.	190	validly interpreted as a Unicode code point.
200		191
201	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
202	Unicode string encoded in UTF-8, giving you a binary string.	193	Unicode string encoded in UTF-8, giving you a binary string.
203		194
204	=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.
…		…
242		233
243	If C<$enable> is false, then the C<encode> method will not escape Unicode	234	If C<$enable> is false, then the C<encode> method will not escape Unicode
244	characters unless required by the JSON syntax or other flags. This results	235	characters unless required by the JSON syntax or other flags. This results
245	in a faster and more compact format.	236	in a faster and more compact format.
246		237
		238	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		239	document.
		240
247	The main use for this flag is to produce JSON texts that can be	241	The main use for this flag is to produce JSON texts that can be
248	transmitted over a 7-bit channel, as the encoded JSON texts will not	242	transmitted over a 7-bit channel, as the encoded JSON texts will not
249	contain any 8 bit characters.	243	contain any 8 bit characters.
250		244
251	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	245	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
…		…
262	will not be affected in any way by this flag, as C<decode> by default	256	will not be affected in any way by this flag, as C<decode> by default
263	expects Unicode, which is a strict superset of latin1.	257	expects Unicode, which is a strict superset of latin1.
264		258
265	If C<$enable> is false, then the C<encode> method will not escape Unicode	259	If C<$enable> is false, then the C<encode> method will not escape Unicode
266	characters unless required by the JSON syntax or other flags.	260	characters unless required by the JSON syntax or other flags.
		261
		262	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		263	document.
267		264
268	The main use for this flag is efficiently encoding binary data as JSON	265	The main use for this flag is efficiently encoding binary data as JSON
269	text, as most octets will not be escaped, resulting in a smaller encoded	266	text, as most octets will not be escaped, resulting in a smaller encoded
270	size. The disadvantage is that the resulting JSON text is encoded	267	size. The disadvantage is that the resulting JSON text is encoded
271	in latin1 (and must correctly be treated as such when storing and	268	in latin1 (and must correctly be treated as such when storing and
…		…
290		287
291	If C<$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
292	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
293	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
294	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.
295		295
296	Example, output UTF-16BE-encoded JSON:	296	Example, output UTF-16BE-encoded JSON:
297		297
298	use Encode;	298	use Encode;
299	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	299	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
422	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
423	by sorting their keys. This is adding a comparatively high overhead.	423	by sorting their keys. This is adding a comparatively high overhead.
424		424
425	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
426	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
427	of the same script).	427	of the same script, and can change even within the same run from 5.18
		428	onwards).
428		429
429	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
430	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,
431	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,
432	as key-value pairs have no inherent ordering in Perl.	433	as key-value pairs have no inherent ordering in Perl.
433		434
434	This setting has no effect when decoding JSON texts.	435	This setting has no effect when decoding JSON texts.
435		436
		437	This setting has currently no effect on tied hashes.
		438
436	=item $json = $json->allow_nonref ([$enable])	439	=item $json = $json->allow_nonref ([$enable])
437		440
438	=item $enabled = $json->get_allow_nonref	441	=item $enabled = $json->get_allow_nonref
439		442
440	If C<$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
…		…
450	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>,
451	resulting in an invalid JSON text:	454	resulting in an invalid JSON text:
452		455
453	JSON::XS->new->allow_nonref->encode ("Hello, World!")	456	JSON::XS->new->allow_nonref->encode ("Hello, World!")
454	=> "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.
455		474
456	=item $json = $json->allow_blessed ([$enable])	475	=item $json = $json->allow_blessed ([$enable])
457		476
458	=item $enabled = $json->get_allow_blessed	477	=item $enabled = $json->get_allow_blessed
459		478
…		…
600	=item $json = $json->max_depth ([$maximum_nesting_depth])	619	=item $json = $json->max_depth ([$maximum_nesting_depth])
601		620
602	=item $max_depth = $json->get_max_depth	621	=item $max_depth = $json->get_max_depth
603		622
604	Sets the maximum nesting level (default C<512>) accepted while encoding	623	Sets the maximum nesting level (default C<512>) accepted while encoding
605	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
606	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
607	stop and croak at that point.	626	point.
608		627
609	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
610	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<[>
611	characters without their matching closing parenthesis crossed to reach a	630	characters without their matching closing parenthesis crossed to reach a
612	given character in a string.	631	given character in a string.
613		632
614	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
615	that the object is only a single hash/object or array.	634	that the object is only a single hash/object or array.
616		635
617	The argument to C<max_depth> will be rounded up to the next highest power
618	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
619	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.
620		642
621	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.
622		644
623	=item $json = $json->max_size ([$maximum_string_size])	645	=item $json = $json->max_size ([$maximum_string_size])
624		646
625	=item $max_size = $json->get_max_size	647	=item $max_size = $json->get_max_size
626		648
627	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
628	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>
629	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
630	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
631	effect on C<encode> (yet).	653	effect on C<encode> (yet).
632		654
633	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
634	power of two (so may be more than requested). If no argument is given, the	656	C<0> is specified).
635	limit check will be deactivated (same as when C<0> is specified).
636		657
637	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.
638		659
639	=item $json_text = $json->encode ($perl_scalar)	660	=item $json_text = $json->encode ($perl_scalar)
640		661
641	Converts the given Perl data structure (a simple scalar or a reference	662	Converts the given Perl value or data structure to its JSON
642	to a hash or array) to its JSON representation. Simple scalars will be	663	representation. Croaks on error.
643	converted into JSON string or number sequences, while references to arrays
644	become JSON arrays and references to hashes become JSON objects. Undefined
645	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
646	nor C<false> values will be generated.
647		664
648	=item $perl_scalar = $json->decode ($json_text)	665	=item $perl_scalar = $json->decode ($json_text)
649		666
650	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,
651	returning the resulting simple scalar or reference. Croaks on error.	668	returning the resulting simple scalar or reference. Croaks on error.
652
653	JSON numbers and strings become simple Perl scalars. JSON arrays become
654	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
655	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
656		669
657	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)	670	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
658		671
659	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
660	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
…		…
669	=> ([], 3)	682	=> ([], 3)
670		683
671	=back	684	=back
672		685
673		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
674	=head1 MAPPING	931	=head1 MAPPING
675		932
676	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
677	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
678	circumstances automatically, preserving round-tripping characteristics	935	circumstances automatically, preserving round-tripping characteristics
…		…
706		963
707	A JSON number becomes either an integer, numeric (floating point) or	964	A JSON number becomes either an integer, numeric (floating point) or
708	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
709	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
710	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
711	might represent more values exactly than (floating point) numbers.	968	might represent more values exactly than floating point numbers.
712		969
713	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
714	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
715	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
716	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).
717		976
718	Numbers containing a fractional or exponential part will always be	977	Numbers containing a fractional or exponential part will always be
719	represented as numeric (floating point) values, possibly at a loss of	978	represented as numeric (floating point) values, possibly at a loss of
720	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).
721		981
722	This might create round-tripping problems as numbers might become strings,	982	Note that precision is not accuracy - binary floating point values cannot
723	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.
724		986
725	=item true, false	987	=item true, false
726		988
727	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>,
728	respectively. They are overloaded to act almost exactly like the numbers	990	respectively. They are overloaded to act almost exactly like the numbers
…		…
765	Other unblessed references are generally not allowed and will cause an	1027	Other unblessed references are generally not allowed and will cause an
766	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
767	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
768	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.
769		1031
770	encode_json [\0,JSON::XS::true] # yields [false,true]	1032	encode_json [\0, JSON::XS::true] # yields [false,true]
771		1033
772	=item JSON::XS::true, JSON::XS::false	1034	=item JSON::XS::true, JSON::XS::false
773		1035
774	These special values become JSON true and JSON false values,	1036	These special values become JSON true and JSON false values,
775	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.
776		1038
777	=item blessed objects	1039	=item blessed objects
778		1040
779	Blessed objects are not allowed. JSON::XS currently tries to encode their	1041	Blessed objects are not directly representable in JSON. See the
780	underlying representation (hash- or arrayref), but this behaviour might	1042	C<allow_blessed> and C<convert_blessed> methods on various options on
781	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.
782		1046
783	=item simple scalars	1047	=item simple scalars
784		1048
785	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
786	difficult objects to encode: JSON::XS will encode undefined scalars as	1050	difficult objects to encode: JSON::XS will encode undefined scalars as
787	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
788	before encoding as JSON strings and anything else as number value:	1052	before encoding as JSON strings, and anything else as number value:
789		1053
790	# dump as number	1054	# dump as number
791	encode_json [2] # yields [2]	1055	encode_json [2] # yields [2]
792	encode_json [-3.0e17] # yields [-3e+17]	1056	encode_json [-3.0e17] # yields [-3e+17]
793	my $value = 5; encode_json [$value] # yields [5]	1057	my $value = 5; encode_json [$value] # yields [5]
…		…
811	my $x = "3"; # some variable containing a string	1075	my $x = "3"; # some variable containing a string
812	$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
813	$x *= 1; # same thing, the choice is yours.	1077	$x *= 1; # same thing, the choice is yours.
814		1078
815	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
816	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.
817		1089
818	=back	1090	=back
819		1091
820		1092
821	=head1 COMPARISON	1093	=head1 ENCODING/CODESET FLAG NOTES
822		1094
823	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
824	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
825	problems (or pleasures) I encountered with various existing JSON modules,	1097	some confusion on what these do, so here is a short comparison:
826	followed by some benchmark values. JSON::XS was designed not to suffer	1098
827	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.
828		1117
829	=over 4	1118	=over 4
830		1119
831	=item JSON 1.07	1120	=item C<utf8> flag disabled
832		1121
833	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).
834		1129
835	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
836	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
837	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).
838		1135
839	No round-tripping (strings get clobbered if they look like numbers, e.g.	1136	=item C<utf8> flag enabled
840	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
841	decode into the number 2.
842		1137
843	=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.
844		1143
845	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.
846		1147
847	Undocumented/buggy Unicode handling.	1148	=item C<latin1> or C<ascii> flags enabled
848		1149
849	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.
850		1153
851	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
852	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).
853		1159
854	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,
855	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.
856		1163
857	Unmaintained (maintainer unresponsive for many months, bugs are not	1164	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
858	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.
859		1168
860	=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.
861		1173
862	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.
863		1176
864	Very inflexible (no human-readable format supported, format pretty much	1177	The main use for C<latin1> is to relatively efficiently store binary data
865	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.
866	single-line compact format for use in a protocol, and preferably a way to
867	generate ASCII-only JSON texts).
868		1179
869	Completely broken (and confusingly documented) Unicode handling (Unicode	1180	The main use for C<ascii> is to force the output to not contain characters
870	escapes are not working properly, you need to set ImplicitUnicode to	1181	with values > 127, which means you can interpret the resulting string
871	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
872		1183	8-bit-encoding, and still get the same data structure back. This is useful
873	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
874	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
875		1186	proper subset of most 8-bit and multibyte encodings in use in the world.
876	Dumping hashes may skip hash values depending on iterator state.
877
878	Unmaintained (maintainer unresponsive for many months, bugs are not
879	getting fixed).
880
881	Does not check input for validity (i.e. will accept non-JSON input and
882	return "something" instead of raising an exception. This is a security
883	issue: imagine two banks transferring money between each other using
884	JSON. One bank might parse a given non-JSON request and deduct money,
885	while the other might reject the transaction with a syntax error. While a
886	good protocol will at least recover, that is extra unnecessary work and
887	the transaction will still not succeed).
888
889	=item JSON::DWIW 0.04
890
891	Very fast. Very natural. Very nice.
892
893	Undocumented Unicode handling (but the best of the pack. Unicode escapes
894	still don't get parsed properly).
895
896	Very inflexible.
897
898	No round-tripping.
899
900	Does not generate valid JSON texts (key strings are often unquoted, empty keys
901	result in nothing being output)
902
903	Does not check input for validity.
904		1187
905	=back	1188	=back
906		1189
907		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
908	=head2 JSON and YAML	1256	=head2 JSON and YAML
909		1257
910	You often hear that JSON is a subset of YAML. This is, however, a mass	1258	You often hear that JSON is a subset of YAML. This is, however, a mass
911	hysteria(*) and very far from the truth. In general, there is no way to	1259	hysteria(*) and very far from the truth (as of the time of this writing),
		1260	so let me state it clearly: I<in general, there is no way to configure
912	configure JSON::XS to output a data structure as valid YAML that works for	1261	JSON::XS to output a data structure as valid YAML> that works in all
913	all cases.	1262	cases.
914		1263
915	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
916	algorithm (subject to change in future versions):	1265	algorithm (subject to change in future versions):
917		1266
918	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1267	my $to_yaml = JSON::XS->new->utf8->space_after (1);
919	my $yaml = $to_yaml->encode ($ref) . "\n";	1268	my $yaml = $to_yaml->encode ($ref) . "\n";
920		1269
921	This will usually generate JSON texts that also parse as valid	1270	This will I<usually> generate JSON texts that also parse as valid
922	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
923	lengths that JSON doesn't have and also has different and incompatible	1272	lengths that JSON doesn't have and also has different and incompatible
924	unicode handling, so you should make sure that your hash keys are	1273	unicode character escape syntax, so you should make sure that your hash
925	noticeably shorter than the 1024 "stream characters" YAML allows and that	1274	keys are noticeably shorter than the 1024 "stream characters" YAML allows
926	you do not have codepoints with values outside the Unicode BMP (basic	1275	and that you do not have characters with codepoint values outside the
927	multilingual page). YAML also does not allow C<\/> sequences in strings	1276	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
928	(which JSON::XS does not I<currently> generate).	1277	sequences in strings (which JSON::XS does not I<currently> generate, but
		1278	other JSON generators might).
929		1279
930	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
931	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
932	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
933	that you will run into severe interoperability problems when you least	1284	high that you will run into severe interoperability problems when you
934	expect it.	1285	least expect it.
935		1286
936	=over 4	1287	=over 4
937		1288
938	=item (*)	1289	=item (*)
939		1290
940	This is spread actively by the YAML team, however. For many years now they	1291	I have been pressured multiple times by Brian Ingerson (one of the
941	claim YAML were a superset of JSON, even when proven otherwise.	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).
942		1298
943	Even the author of this manpage was at some point accused of providing	1299	In my opinion, instead of pressuring and insulting people who actually
944	"incorrect" information, despite the evidence presented (claims ranged	1300	clarify issues with YAML and the wrong statements of some of its
945	from "your documentation contains inaccurate and negative statements about	1301	proponents, I would kindly suggest reading the JSON spec (which is not
946	YAML" (the only negative comment is this footnote, and it didn't exist	1302	that difficult or long) and finally make YAML compatible to it, and
947	back then; the question on which claims were inaccurate was never answered	1303	educating users about the changes, instead of spreading lies about the
948	etc.) to "the YAML spec is not up-to-date" (the real and suppsedly	1304	real compatibility for many I<years> and trying to silence people who
949	JSON-compatible spec is apparently not currently publicly available)	1305	point out that it isn't true.
950	to actual requests to replace this section by incorrect information,
951	suppressing information about the real problem).
952		1306
953	So whenever you are told that YAML was a superset of JSON, first check	1307	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
954	wether it is really true (it might be when you check it, but it cetrainly	1308	though the incompatibilities have been documented (and are known to Brian)
955	is not true when this was written). I would much prefer if the YAML team	1309	for many years and the spec makes explicit claims that YAML is a superset
956	would spent their time on actually making JSON compatibility a truth	1310	of JSON. It would be so easy to fix, but apparently, bullying people and
957	(JSON, after all, has a very small and simple specification) instead of	1311	corrupting userdata is so much easier.
958	trying to lobby/force people into reporting untruths.
959		1312
960	=back	1313	=back
961		1314
962		1315
963	=head2 SPEED	1316	=head2 SPEED
…		…
965	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
966	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
967	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
968	system.	1321	system.
969		1322
970	First comes a comparison between various modules using a very short	1323	First comes a comparison between various modules using
971	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>).
972		1326
973	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1327	{"method": "handleMessage", "params": ["user1",
974	"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]}
975		1330
976	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
977	the functional interface, while JSON::XS/2 uses the OO interface	1332	the functional interface, while JSON::XS/2 uses the OO interface
978	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1333	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
979	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:
980		1336
981	module \| encode \| decode \|	1337	module \| encode \| decode \|
982	-----------\|------------\|------------\|	1338	--------------\|------------\|------------\|
983	JSON 1.x \| 4990.842 \| 4088.813 \|	1339	JSON::DWIW/DS \| 86302.551 \| 102300.098 \|
984	JSON::DWIW \| 51653.990 \| 71575.154 \|	1340	JSON::DWIW/FJ \| 86302.551 \| 75983.768 \|
985	JSON::PC \| 65948.176 \| 74631.744 \|	1341	JSON::PP \| 15827.562 \| 6638.658 \|
986	JSON::PP \| 8931.652 \| 3817.168 \|	1342	JSON::Syck \| 63358.066 \| 47662.545 \|
987	JSON::Syck \| 24877.248 \| 27776.848 \|	1343	JSON::XS \| 511500.488 \| 511500.488 \|
988	JSON::XS \| 388361.481 \| 227951.304 \|	1344	JSON::XS/2 \| 291271.111 \| 388361.481 \|
989	JSON::XS/2 \| 227951.304 \| 218453.333 \|	1345	JSON::XS/3 \| 361577.931 \| 361577.931 \|
990	JSON::XS/3 \| 338250.323 \| 218453.333 \|	1346	Storable \| 66788.280 \| 265462.278 \|
991	Storable \| 16500.016 \| 135300.129 \|
992	-----------+------------+------------+	1347	--------------+------------+------------+
993		1348
994	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,
995	about three times faster on decoding, and over forty times faster	1350	about five times faster on decoding, and over thirty to seventy times
996	than JSON, even with pretty-printing and key sorting. It also compares	1351	faster than JSON's pure perl implementation. It also compares favourably
997	favourably to Storable for small amounts of data.	1352	to Storable for small amounts of data.
998		1353
999	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1354	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
1000	search API (http://nanoref.com/yahooapis/mgPdGg):	1355	search API (L<http://dist.schmorp.de/misc/json/long.json>).
1001		1356
1002	module \| encode \| decode \|	1357	module \| encode \| decode \|
1003	-----------\|------------\|------------\|	1358	--------------\|------------\|------------\|
1004	JSON 1.x \| 55.260 \| 34.971 \|	1359	JSON::DWIW/DS \| 1647.927 \| 2673.916 \|
1005	JSON::DWIW \| 825.228 \| 1082.513 \|	1360	JSON::DWIW/FJ \| 1630.249 \| 2596.128 \|
1006	JSON::PC \| 3571.444 \| 2394.829 \|
1007	JSON::PP \| 210.987 \| 32.574 \|	1361	JSON::PP \| 400.640 \| 62.311 \|
1008	JSON::Syck \| 552.551 \| 787.544 \|	1362	JSON::Syck \| 1481.040 \| 1524.869 \|
1009	JSON::XS \| 5780.463 \| 4854.519 \|	1363	JSON::XS \| 20661.596 \| 9541.183 \|
1010	JSON::XS/2 \| 3869.998 \| 4798.975 \|	1364	JSON::XS/2 \| 10683.403 \| 9416.938 \|
1011	JSON::XS/3 \| 5862.880 \| 4798.975 \|	1365	JSON::XS/3 \| 20661.596 \| 9400.054 \|
1012	Storable \| 4445.002 \| 5235.027 \|	1366	Storable \| 19765.806 \| 10000.725 \|
1013	-----------+------------+------------+	1367	--------------+------------+------------+
1014		1368
1015	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
1016	decodes faster).	1370	decodes a bit faster).
1017		1371
1018	On large strings containing lots of high Unicode characters, some modules	1372	On large strings containing lots of high Unicode characters, some modules
1019	(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
1020	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
1021	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
…		…
1047	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
1048	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
1049	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
1050	C<max_depth> method.	1404	C<max_depth> method.
1051		1405
1052	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
1053	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...
1054	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.
1055		1413
1056	If you are using JSON::XS to return packets to consumption	1414	If you are using JSON::XS to return packets to consumption
1057	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
1058	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
1059	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
1060	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
1061	browser developers care only for features, not about getting security	1419	it, as major browser developers care only for features, not about getting
1062	right).	1420	security right).
1063		1421
1064		1422
1065	=head1 THREADS	1423	=head1 THREADS
1066		1424
1067	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
1068	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
1069	horribly slow so-called "threads" which are simply slow and bloated	1427	horribly slow so-called "threads" which are simply slow and bloated
1070	process simulations - use fork, its I<much> faster, cheaper, better).	1428	process simulations - use fork, it's I<much> faster, cheaper, better).
1071		1429
1072	(It might actually work, but you have been warned).	1430	(It might actually work, but you have been warned).
1073		1431
1074		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
1075	=head1 BUGS	1451	=head1 BUGS
1076		1452
1077	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
1078	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
1079	still relatively early in its development. If you keep reporting bugs they	1455	keep reporting bugs they will be fixed swiftly, though.
1080	will be fixed swiftly, though.
1081		1456
1082	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
1083	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.
1084		1459
1085	=cut	1460	=cut
…		…
1105	"--" => sub { $_[0] = ${$_[0]} - 1 },	1480	"--" => sub { $_[0] = ${$_[0]} - 1 },
1106	fallback => 1;	1481	fallback => 1;
1107		1482
1108	1;	1483	1;
1109		1484
		1485	=head1 SEE ALSO
		1486
		1487	The F<json_xs> command line utility for quick experiments.
		1488
1110	=head1 AUTHOR	1489	=head1 AUTHOR
1111		1490
1112	Marc Lehmann <schmorp@schmorp.de>	1491	Marc Lehmann <schmorp@schmorp.de>
1113	http://home.schmorp.de/	1492	http://home.schmorp.de/
1114		1493

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Comparing JSON-XS/XS.pm (file contents): Revision 1.82 by root, Sun Dec 30 21:24:57 2007 UTC vs. Revision 1.141 by root, Fri Oct 25 19:53:08 2013 UTC

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Revision 1.82 by root, Sun Dec 30 21:24:57 2007 UTC vs.
Revision 1.141 by root, Fri Oct 25 19:53:08 2013 UTC