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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.79 by root, Wed Dec 19 11:42:52 2007 UTC vs.
Revision 1.144 by root, Mon Oct 28 23:19:54 2013 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	3	JSON::XS - JSON serialising/deserialising, done correctly and fast
		4
		5	=encoding utf-8
4		6
5	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ	7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
6	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)	8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
7		9
8	=head1 SYNOPSIS	10	=head1 SYNOPSIS
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
		114	use Types::Serialiser ();
		115
123	=head1 FUNCTIONAL INTERFACE	116	=head1 FUNCTIONAL INTERFACE
124		117
125	The following convenience methods are provided by this module. They are	118	The following convenience methods are provided by this module. They are
126	exported by default:	119	exported by default:
127		120
…		…
134		127
135	This function call is functionally identical to:	128	This function call is functionally identical to:
136		129
137	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	130	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
138		131
139	except being faster.	132	Except being faster.
140		133
141	=item $perl_scalar = decode_json $json_text	134	=item $perl_scalar = decode_json $json_text
142		135
143	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries	136	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	137	to parse that as an UTF-8 encoded JSON text, returning the resulting
…		…
146		139
147	This function call is functionally identical to:	140	This function call is functionally identical to:
148		141
149	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	142	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
150		143
151	except being faster.	144	Except being faster.
152
153	=item $is_boolean = JSON::XS::is_bool $scalar
154
155	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
157	and are used to represent JSON C<true> and C<false> values in Perl.
158
159	See MAPPING, below, for more information on how JSON values are mapped to
160	Perl.
161		145
162	=back	146	=back
163		147
164		148
165	=head1 A FEW NOTES ON UNICODE AND PERL	149	=head1 A FEW NOTES ON UNICODE AND PERL
…		…
174	This enables you to store Unicode characters as single characters in a	158	This enables you to store Unicode characters as single characters in a
175	Perl string - very natural.	159	Perl string - very natural.
176		160
177	=item 2. Perl does I<not> associate an encoding with your strings.	161	=item 2. Perl does I<not> associate an encoding with your strings.
178		162
179	Unless you force it to, e.g. when matching it against a regex, or printing	163	... 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	164	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	165	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	166	on various settings. In no case is an encoding stored together with your
183	I<use> that decides encoding, not any magical metadata.	167	data, it is I<use> that decides encoding, not any magical meta data.
184		168
185	=item 3. The internal utf-8 flag has no meaning with regards to the	169	=item 3. The internal utf-8 flag has no meaning with regards to the
186	encoding of your string.	170	encoding of your string.
187		171
188	Just ignore that flag unless you debug a Perl bug, a module written in	172	Just ignore that flag unless you debug a Perl bug, a module written in
…		…
194		178
195	If you didn't know about that flag, just the better, pretend it doesn't	179	If you didn't know about that flag, just the better, pretend it doesn't
196	exist.	180	exist.
197		181
198	=item 4. A "Unicode String" is simply a string where each character can be	182	=item 4. A "Unicode String" is simply a string where each character can be
199	validly interpreted as a Unicode codepoint.	183	validly interpreted as a Unicode code point.
200		184
201	If you have UTF-8 encoded data, it is no longer a Unicode string, but a	185	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.	186	Unicode string encoded in UTF-8, giving you a binary string.
203		187
204	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.	188	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
…		…
242		226
243	If C<$enable> is false, then the C<encode> method will not escape Unicode	227	If C<$enable> is false, then the C<encode> method will not escape Unicode
244	characters unless required by the JSON syntax or other flags. This results	228	characters unless required by the JSON syntax or other flags. This results
245	in a faster and more compact format.	229	in a faster and more compact format.
246		230
		231	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		232	document.
		233
247	The main use for this flag is to produce JSON texts that can be	234	The main use for this flag is to produce JSON texts that can be
248	transmitted over a 7-bit channel, as the encoded JSON texts will not	235	transmitted over a 7-bit channel, as the encoded JSON texts will not
249	contain any 8 bit characters.	236	contain any 8 bit characters.
250		237
251	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	238	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
…		…
262	will not be affected in any way by this flag, as C<decode> by default	249	will not be affected in any way by this flag, as C<decode> by default
263	expects Unicode, which is a strict superset of latin1.	250	expects Unicode, which is a strict superset of latin1.
264		251
265	If C<$enable> is false, then the C<encode> method will not escape Unicode	252	If C<$enable> is false, then the C<encode> method will not escape Unicode
266	characters unless required by the JSON syntax or other flags.	253	characters unless required by the JSON syntax or other flags.
		254
		255	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		256	document.
267		257
268	The main use for this flag is efficiently encoding binary data as JSON	258	The main use for this flag is efficiently encoding binary data as JSON
269	text, as most octets will not be escaped, resulting in a smaller encoded	259	text, as most octets will not be escaped, resulting in a smaller encoded
270	size. The disadvantage is that the resulting JSON text is encoded	260	size. The disadvantage is that the resulting JSON text is encoded
271	in latin1 (and must correctly be treated as such when storing and	261	in latin1 (and must correctly be treated as such when storing and
…		…
290		280
291	If C<$enable> is false, then the C<encode> method will return the JSON	281	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	282	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	283	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.	284	to be done yourself, e.g. using the Encode module.
		285
		286	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		287	document.
295		288
296	Example, output UTF-16BE-encoded JSON:	289	Example, output UTF-16BE-encoded JSON:
297		290
298	use Encode;	291	use Encode;
299	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	292	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
422	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	415	If C<$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.	416	by sorting their keys. This is adding a comparatively high overhead.
424		417
425	If C<$enable> is false, then the C<encode> method will output key-value	418	If C<$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	419	pairs in the order Perl stores them (which will likely change between runs
427	of the same script).	420	of the same script, and can change even within the same run from 5.18
		421	onwards).
428		422
429	This option is useful if you want the same data structure to be encoded as	423	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,	424	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,	425	the same hash might be encoded differently even if contains the same data,
432	as key-value pairs have no inherent ordering in Perl.	426	as key-value pairs have no inherent ordering in Perl.
433		427
434	This setting has no effect when decoding JSON texts.	428	This setting has no effect when decoding JSON texts.
435		429
		430	This setting has currently no effect on tied hashes.
		431
436	=item $json = $json->allow_nonref ([$enable])	432	=item $json = $json->allow_nonref ([$enable])
437		433
438	=item $enabled = $json->get_allow_nonref	434	=item $enabled = $json->get_allow_nonref
439		435
440	If C<$enable> is true (or missing), then the C<encode> method can convert a	436	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>,	446	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
451	resulting in an invalid JSON text:	447	resulting in an invalid JSON text:
452		448
453	JSON::XS->new->allow_nonref->encode ("Hello, World!")	449	JSON::XS->new->allow_nonref->encode ("Hello, World!")
454	=> "Hello, World!"	450	=> "Hello, World!"
		451
		452	=item $json = $json->allow_unknown ([$enable])
		453
		454	=item $enabled = $json->get_allow_unknown
		455
		456	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		457	exception when it encounters values it cannot represent in JSON (for
		458	example, filehandles) but instead will encode a JSON C<null> value. Note
		459	that blessed objects are not included here and are handled separately by
		460	c<allow_nonref>.
		461
		462	If C<$enable> is false (the default), then C<encode> will throw an
		463	exception when it encounters anything it cannot encode as JSON.
		464
		465	This option does not affect C<decode> in any way, and it is recommended to
		466	leave it off unless you know your communications partner.
455		467
456	=item $json = $json->allow_blessed ([$enable])	468	=item $json = $json->allow_blessed ([$enable])
457		469
458	=item $enabled = $json->get_allow_blessed	470	=item $enabled = $json->get_allow_blessed
459		471
…		…
600	=item $json = $json->max_depth ([$maximum_nesting_depth])	612	=item $json = $json->max_depth ([$maximum_nesting_depth])
601		613
602	=item $max_depth = $json->get_max_depth	614	=item $max_depth = $json->get_max_depth
603		615
604	Sets the maximum nesting level (default C<512>) accepted while encoding	616	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	617	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	618	data structure, then the encoder and decoder will stop and croak at that
607	stop and croak at that point.	619	point.
608		620
609	Nesting level is defined by number of hash- or arrayrefs that the encoder	621	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<[>	622	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	623	characters without their matching closing parenthesis crossed to reach a
612	given character in a string.	624	given character in a string.
613		625
614	Setting the maximum depth to one disallows any nesting, so that ensures	626	Setting the maximum depth to one disallows any nesting, so that ensures
615	that the object is only a single hash/object or array.	627	that the object is only a single hash/object or array.
616		628
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	629	If no argument is given, the highest possible setting will be used, which
619	used, which is rarely useful.	630	is rarely useful.
		631
		632	Note that nesting is implemented by recursion in C. The default value has
		633	been chosen to be as large as typical operating systems allow without
		634	crashing.
620		635
621	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	636	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
622		637
623	=item $json = $json->max_size ([$maximum_string_size])	638	=item $json = $json->max_size ([$maximum_string_size])
624		639
625	=item $max_size = $json->get_max_size	640	=item $max_size = $json->get_max_size
626		641
627	Set the maximum length a JSON text may have (in bytes) where decoding is	642	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>	643	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	644	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	645	attempt to decode the string but throw an exception. This setting has no
631	effect on C<encode> (yet).	646	effect on C<encode> (yet).
632		647
633	The argument to C<max_size> will be rounded up to the next B<highest>	648	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	649	C<0> is specified).
635	limit check will be deactivated (same as when C<0> is specified).
636		650
637	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	651	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
638		652
639	=item $json_text = $json->encode ($perl_scalar)	653	=item $json_text = $json->encode ($perl_scalar)
640		654
641	Converts the given Perl data structure (a simple scalar or a reference	655	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	656	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		657
648	=item $perl_scalar = $json->decode ($json_text)	658	=item $perl_scalar = $json->decode ($json_text)
649		659
650	The opposite of C<encode>: expects a JSON text and tries to parse it,	660	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.	661	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		662
657	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)	663	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
658		664
659	This works like the C<decode> method, but instead of raising an exception	665	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	666	when there is trailing garbage after the first JSON object, it will
661	silently stop parsing there and return the number of characters consumed	667	silently stop parsing there and return the number of characters consumed
662	so far.	668	so far.
663		669
664	This is useful if your JSON texts are not delimited by an outer protocol	670	This is useful if your JSON texts are not delimited by an outer protocol
665	(which is not the brightest thing to do in the first place) and you need
666	to know where the JSON text ends.	671	and you need to know where the JSON text ends.
667		672
668	JSON::XS->new->decode_prefix ("[1] the tail")	673	JSON::XS->new->decode_prefix ("[1] the tail")
669	=> ([], 3)	674	=> ([], 3)
670		675
671	=back	676	=back
		677
		678
		679	=head1 INCREMENTAL PARSING
		680
		681	In some cases, there is the need for incremental parsing of JSON
		682	texts. While this module always has to keep both JSON text and resulting
		683	Perl data structure in memory at one time, it does allow you to parse a
		684	JSON stream incrementally. It does so by accumulating text until it has
		685	a full JSON object, which it then can decode. This process is similar to
		686	using C<decode_prefix> to see if a full JSON object is available, but
		687	is much more efficient (and can be implemented with a minimum of method
		688	calls).
		689
		690	JSON::XS will only attempt to parse the JSON text once it is sure it
		691	has enough text to get a decisive result, using a very simple but
		692	truly incremental parser. This means that it sometimes won't stop as
		693	early as the full parser, for example, it doesn't detect mismatched
		694	parentheses. The only thing it guarantees is that it starts decoding as
		695	soon as a syntactically valid JSON text has been seen. This means you need
		696	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		697	parsing in the presence if syntax errors.
		698
		699	The following methods implement this incremental parser.
		700
		701	=over 4
		702
		703	=item [void, scalar or list context] = $json->incr_parse ([$string])
		704
		705	This is the central parsing function. It can both append new text and
		706	extract objects from the stream accumulated so far (both of these
		707	functions are optional).
		708
		709	If C<$string> is given, then this string is appended to the already
		710	existing JSON fragment stored in the C<$json> object.
		711
		712	After that, if the function is called in void context, it will simply
		713	return without doing anything further. This can be used to add more text
		714	in as many chunks as you want.
		715
		716	If the method is called in scalar context, then it will try to extract
		717	exactly I<one> JSON object. If that is successful, it will return this
		718	object, otherwise it will return C<undef>. If there is a parse error,
		719	this method will croak just as C<decode> would do (one can then use
		720	C<incr_skip> to skip the erroneous part). This is the most common way of
		721	using the method.
		722
		723	And finally, in list context, it will try to extract as many objects
		724	from the stream as it can find and return them, or the empty list
		725	otherwise. For this to work, there must be no separators between the JSON
		726	objects or arrays, instead they must be concatenated back-to-back. If
		727	an error occurs, an exception will be raised as in the scalar context
		728	case. Note that in this case, any previously-parsed JSON texts will be
		729	lost.
		730
		731	Example: Parse some JSON arrays/objects in a given string and return
		732	them.
		733
		734	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		735
		736	=item $lvalue_string = $json->incr_text
		737
		738	This method returns the currently stored JSON fragment as an lvalue, that
		739	is, you can manipulate it. This I<only> works when a preceding call to
		740	C<incr_parse> in I<scalar context> successfully returned an object. Under
		741	all other circumstances you must not call this function (I mean it.
		742	although in simple tests it might actually work, it I<will> fail under
		743	real world conditions). As a special exception, you can also call this
		744	method before having parsed anything.
		745
		746	This function is useful in two cases: a) finding the trailing text after a
		747	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		748	(such as commas).
		749
		750	=item $json->incr_skip
		751
		752	This will reset the state of the incremental parser and will remove
		753	the parsed text from the input buffer so far. This is useful after
		754	C<incr_parse> died, in which case the input buffer and incremental parser
		755	state is left unchanged, to skip the text parsed so far and to reset the
		756	parse state.
		757
		758	The difference to C<incr_reset> is that only text until the parse error
		759	occurred is removed.
		760
		761	=item $json->incr_reset
		762
		763	This completely resets the incremental parser, that is, after this call,
		764	it will be as if the parser had never parsed anything.
		765
		766	This is useful if you want to repeatedly parse JSON objects and want to
		767	ignore any trailing data, which means you have to reset the parser after
		768	each successful decode.
		769
		770	=back
		771
		772	=head2 LIMITATIONS
		773
		774	All options that affect decoding are supported, except
		775	C<allow_nonref>. The reason for this is that it cannot be made to work
		776	sensibly: JSON objects and arrays are self-delimited, i.e. you can
		777	concatenate them back to back and still decode them perfectly. This does
		778	not hold true for JSON numbers, however.
		779
		780	For example, is the string C<1> a single JSON number, or is it simply the
		781	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		782	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		783	takes the conservative route and disallows this case.
		784
		785	=head2 EXAMPLES
		786
		787	Some examples will make all this clearer. First, a simple example that
		788	works similarly to C<decode_prefix>: We want to decode the JSON object at
		789	the start of a string and identify the portion after the JSON object:
		790
		791	my $text = "[1,2,3] hello";
		792
		793	my $json = new JSON::XS;
		794
		795	my $obj = $json->incr_parse ($text)
		796	or die "expected JSON object or array at beginning of string";
		797
		798	my $tail = $json->incr_text;
		799	# $tail now contains " hello"
		800
		801	Easy, isn't it?
		802
		803	Now for a more complicated example: Imagine a hypothetical protocol where
		804	you read some requests from a TCP stream, and each request is a JSON
		805	array, without any separation between them (in fact, it is often useful to
		806	use newlines as "separators", as these get interpreted as whitespace at
		807	the start of the JSON text, which makes it possible to test said protocol
		808	with C<telnet>...).
		809
		810	Here is how you'd do it (it is trivial to write this in an event-based
		811	manner):
		812
		813	my $json = new JSON::XS;
		814
		815	# read some data from the socket
		816	while (sysread $socket, my $buf, 4096) {
		817
		818	# split and decode as many requests as possible
		819	for my $request ($json->incr_parse ($buf)) {
		820	# act on the $request
		821	}
		822	}
		823
		824	Another complicated example: Assume you have a string with JSON objects
		825	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		826	[3]>). To parse them, we have to skip the commas between the JSON texts,
		827	and here is where the lvalue-ness of C<incr_text> comes in useful:
		828
		829	my $text = "[1],[2], [3]";
		830	my $json = new JSON::XS;
		831
		832	# void context, so no parsing done
		833	$json->incr_parse ($text);
		834
		835	# now extract as many objects as possible. note the
		836	# use of scalar context so incr_text can be called.
		837	while (my $obj = $json->incr_parse) {
		838	# do something with $obj
		839
		840	# now skip the optional comma
		841	$json->incr_text =~ s/^ \s* , //x;
		842	}
		843
		844	Now lets go for a very complex example: Assume that you have a gigantic
		845	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		846	but you cannot load it into memory fully (this has actually happened in
		847	the real world :).
		848
		849	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		850	can still help you: You implement a (very simple) array parser and let
		851	JSON decode the array elements, which are all full JSON objects on their
		852	own (this wouldn't work if the array elements could be JSON numbers, for
		853	example):
		854
		855	my $json = new JSON::XS;
		856
		857	# open the monster
		858	open my $fh, "<bigfile.json"
		859	or die "bigfile: $!";
		860
		861	# first parse the initial "["
		862	for (;;) {
		863	sysread $fh, my $buf, 65536
		864	or die "read error: $!";
		865	$json->incr_parse ($buf); # void context, so no parsing
		866
		867	# Exit the loop once we found and removed(!) the initial "[".
		868	# In essence, we are (ab-)using the $json object as a simple scalar
		869	# we append data to.
		870	last if $json->incr_text =~ s/^ \s* \[ //x;
		871	}
		872
		873	# now we have the skipped the initial "[", so continue
		874	# parsing all the elements.
		875	for (;;) {
		876	# in this loop we read data until we got a single JSON object
		877	for (;;) {
		878	if (my $obj = $json->incr_parse) {
		879	# do something with $obj
		880	last;
		881	}
		882
		883	# add more data
		884	sysread $fh, my $buf, 65536
		885	or die "read error: $!";
		886	$json->incr_parse ($buf); # void context, so no parsing
		887	}
		888
		889	# in this loop we read data until we either found and parsed the
		890	# separating "," between elements, or the final "]"
		891	for (;;) {
		892	# first skip whitespace
		893	$json->incr_text =~ s/^\s*//;
		894
		895	# if we find "]", we are done
		896	if ($json->incr_text =~ s/^\]//) {
		897	print "finished.\n";
		898	exit;
		899	}
		900
		901	# if we find ",", we can continue with the next element
		902	if ($json->incr_text =~ s/^,//) {
		903	last;
		904	}
		905
		906	# if we find anything else, we have a parse error!
		907	if (length $json->incr_text) {
		908	die "parse error near ", $json->incr_text;
		909	}
		910
		911	# else add more data
		912	sysread $fh, my $buf, 65536
		913	or die "read error: $!";
		914	$json->incr_parse ($buf); # void context, so no parsing
		915	}
		916
		917	This is a complex example, but most of the complexity comes from the fact
		918	that we are trying to be correct (bear with me if I am wrong, I never ran
		919	the above example :).
		920
672		921
673		922
674	=head1 MAPPING	923	=head1 MAPPING
675		924
676	This section describes how JSON::XS maps Perl values to JSON values and	925	This section describes how JSON::XS maps Perl values to JSON values and
…		…
706		955
707	A JSON number becomes either an integer, numeric (floating point) or	956	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	957	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	958	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	959	the conversion details, but an integer may take slightly less memory and
711	might represent more values exactly than (floating point) numbers.	960	might represent more values exactly than floating point numbers.
712		961
713	If the number consists of digits only, JSON::XS will try to represent	962	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	963	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	964	a numeric (floating point) value if that is possible without loss of
716	precision. Otherwise it will preserve the number as a string value.	965	precision. Otherwise it will preserve the number as a string value (in
		966	which case you lose roundtripping ability, as the JSON number will be
		967	re-encoded to a JSON string).
717		968
718	Numbers containing a fractional or exponential part will always be	969	Numbers containing a fractional or exponential part will always be
719	represented as numeric (floating point) values, possibly at a loss of	970	represented as numeric (floating point) values, possibly at a loss of
720	precision.	971	precision (in which case you might lose perfect roundtripping ability, but
		972	the JSON number will still be re-encoded as a JSON number).
721		973
722	This might create round-tripping problems as numbers might become strings,	974	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.	975	represent most decimal fractions exactly, and when converting from and to
		976	floating point, JSON::XS only guarantees precision up to but not including
		977	the least significant bit.
724		978
725	=item true, false	979	=item true, false
726		980
727	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	981	These JSON atoms become C<Types::Serialiser::true> and
728	respectively. They are overloaded to act almost exactly like the numbers	982	C<Types::Serialiser::false>, respectively. They are overloaded to act
729	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using	983	almost exactly like the numbers C<1> and C<0>. You can check whether
730	the C<JSON::XS::is_bool> function.	984	a scalar is a JSON boolean by using the C<Types::Serialiser::is_bool>
		985	function (after C<use Types::Serialier>, of course).
731		986
732	=item null	987	=item null
733		988
734	A JSON null atom becomes C<undef> in Perl.	989	A JSON null atom becomes C<undef> in Perl.
735		990
…		…
744		999
745	=over 4	1000	=over 4
746		1001
747	=item hash references	1002	=item hash references
748		1003
749	Perl hash references become JSON objects. As there is no inherent ordering	1004	Perl hash references become JSON objects. As there is no inherent
750	in hash keys (or JSON objects), they will usually be encoded in a	1005	ordering in hash keys (or JSON objects), they will usually be encoded
751	pseudo-random order that can change between runs of the same program but	1006	in a pseudo-random order. JSON::XS can optionally sort the hash keys
752	stays generally the same within a single run of a program. JSON::XS can	1007	(determined by the I<canonical> flag), so the same datastructure will
753	optionally sort the hash keys (determined by the I<canonical> flag), so	1008	serialise to the same JSON text (given same settings and version of
754	the same datastructure will serialise to the same JSON text (given same	1009	JSON::XS), but this incurs a runtime overhead and is only rarely useful,
755	settings and version of JSON::XS), but this incurs a runtime overhead	1010	e.g. when you want to compare some JSON text against another for equality.
756	and is only rarely useful, e.g. when you want to compare some JSON text
757	against another for equality.
758		1011
759	=item array references	1012	=item array references
760		1013
761	Perl array references become JSON arrays.	1014	Perl array references become JSON arrays.
762		1015
763	=item other references	1016	=item other references
764		1017
765	Other unblessed references are generally not allowed and will cause an	1018	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	1019	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	1020	C<1>, which get turned into C<false> and C<true> atoms in JSON.
768	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
769		1021
		1022	Since C<JSON::XS> uses the boolean model from L<Types::Serialiser>, you
		1023	can also C<use Types::Serialiser> and then use C<Types::Serialiser::false>
		1024	and C<Types::Serialiser::true> to improve readability.
		1025
		1026	use Types::Serialiser;
770	encode_json [\0,JSON::XS::true] # yields [false,true]	1027	encode_json [\0, Types::Serialiser::true] # yields [false,true]
771		1028
772	=item JSON::XS::true, JSON::XS::false	1029	=item Types::Serialiser::true, Types::Serialiser::false
773		1030
774	These special values become JSON true and JSON false values,	1031	These special values from the L<Types::Serialiser> module become JSON true
775	respectively. You can also use C<\1> and C<\0> directly if you want.	1032	and JSON false values, respectively. You can also use C<\1> and C<\0>
		1033	directly if you want.
776		1034
777	=item blessed objects	1035	=item blessed objects
778		1036
779	Blessed objects are not allowed. JSON::XS currently tries to encode their	1037	Blessed objects are not directly representable in JSON. See the
780	underlying representation (hash- or arrayref), but this behaviour might	1038	C<allow_blessed> and C<convert_blessed> methods on various options on
781	change in future versions.	1039	how to deal with this: basically, you can choose between throwing an
		1040	exception, encoding the reference as if it weren't blessed, or provide
		1041	your own serialiser method.
782		1042
783	=item simple scalars	1043	=item simple scalars
784		1044
785	Simple Perl scalars (any scalar that is not a reference) are the most	1045	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	1046	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	1047	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:	1048	before encoding as JSON strings, and anything else as number value:
789		1049
790	# dump as number	1050	# dump as number
791	encode_json [2] # yields [2]	1051	encode_json [2] # yields [2]
792	encode_json [-3.0e17] # yields [-3e+17]	1052	encode_json [-3.0e17] # yields [-3e+17]
793	my $value = 5; encode_json [$value] # yields [5]	1053	my $value = 5; encode_json [$value] # yields [5]
…		…
811	my $x = "3"; # some variable containing a string	1071	my $x = "3"; # some variable containing a string
812	$x += 0; # numify it, ensuring it will be dumped as a number	1072	$x += 0; # numify it, ensuring it will be dumped as a number
813	$x *= 1; # same thing, the choice is yours.	1073	$x *= 1; # same thing, the choice is yours.
814		1074
815	You can not currently force the type in other, less obscure, ways. Tell me	1075	You can not currently force the type in other, less obscure, ways. Tell me
816	if you need this capability.	1076	if you need this capability (but don't forget to explain why it's needed
		1077	:).
		1078
		1079	Note that numerical precision has the same meaning as under Perl (so
		1080	binary to decimal conversion follows the same rules as in Perl, which
		1081	can differ to other languages). Also, your perl interpreter might expose
		1082	extensions to the floating point numbers of your platform, such as
		1083	infinities or NaN's - these cannot be represented in JSON, and it is an
		1084	error to pass those in.
817		1085
818	=back	1086	=back
819		1087
820		1088
821	=head1 COMPARISON	1089	=head1 ENCODING/CODESET FLAG NOTES
822		1090
823	As already mentioned, this module was created because none of the existing	1091	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	1092	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,	1093	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	1094
827	from any of these problems or limitations.	1095	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1096	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1097	control whether C<encode> escapes character values outside their respective
		1098	codeset range. Neither of these flags conflict with each other, although
		1099	some combinations make less sense than others.
		1100
		1101	Care has been taken to make all flags symmetrical with respect to
		1102	C<encode> and C<decode>, that is, texts encoded with any combination of
		1103	these flag values will be correctly decoded when the same flags are used
		1104	- in general, if you use different flag settings while encoding vs. when
		1105	decoding you likely have a bug somewhere.
		1106
		1107	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1108	simply an abstract set of character-codepoint pairs, while an encoding
		1109	takes those codepoint numbers and I<encodes> them, in our case into
		1110	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1111	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1112	the same time, which can be confusing.
828		1113
829	=over 4	1114	=over 4
830		1115
831	=item JSON 1.07	1116	=item C<utf8> flag disabled
832		1117
833	Slow (but very portable, as it is written in pure Perl).	1118	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1119	and expect Unicode strings, that is, characters with high ordinal Unicode
		1120	values (> 255) will be encoded as such characters, and likewise such
		1121	characters are decoded as-is, no changes to them will be done, except
		1122	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1123	respectively (to Perl, these are the same thing in strings unless you do
		1124	funny/weird/dumb stuff).
834		1125
835	Undocumented/buggy Unicode handling (how JSON handles Unicode values is	1126	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	1127	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).	1128	the encoding for you (for example, when printing to a terminal using a
		1129	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1130	to UTF-8 encode your data first and have Perl encode it another time).
838		1131
839	No round-tripping (strings get clobbered if they look like numbers, e.g.	1132	=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		1133
843	=item JSON::PC 0.01	1134	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1135	characters using the corresponding UTF-8 multi-byte sequence, and will
		1136	expect your input strings to be encoded as UTF-8, that is, no "character"
		1137	of the input string must have any value > 255, as UTF-8 does not allow
		1138	that.
844		1139
845	Very fast.	1140	The C<utf8> flag therefore switches between two modes: disabled means you
		1141	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1142	octet/binary string in Perl.
846		1143
847	Undocumented/buggy Unicode handling.	1144	=item C<latin1> or C<ascii> flags enabled
848		1145
849	No round-tripping.	1146	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1147	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1148	characters as specified by the C<utf8> flag.
850		1149
851	Has problems handling many Perl values (e.g. regex results and other magic	1150	If C<utf8> is disabled, then the result is also correctly encoded in those
852	values will make it croak).	1151	character sets (as both are proper subsets of Unicode, meaning that a
		1152	Unicode string with all character values < 256 is the same thing as a
		1153	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1154	the same thing as an ASCII string in Perl).
853		1155
854	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1156	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
855	which is not a valid JSON text.	1157	regardless of these flags, just some more characters will be escaped using
		1158	C<\uXXXX> then before.
856		1159
857	Unmaintained (maintainer unresponsive for many months, bugs are not	1160	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
858	getting fixed).	1161	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1162	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1163	a subset of Unicode), while ASCII is.
859		1164
860	=item JSON::Syck 0.21	1165	Surprisingly, C<decode> will ignore these flags and so treat all input
		1166	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1167	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1168	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
861		1169
862	Very buggy (often crashes).	1170	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1171	they only govern when the JSON output engine escapes a character or not.
863		1172
864	Very inflexible (no human-readable format supported, format pretty much	1173	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	1174	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		1175
869	Completely broken (and confusingly documented) Unicode handling (Unicode	1176	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	1177	with values > 127, which means you can interpret the resulting string
871	I<different> values on en- and decoding to get symmetric behaviour).	1178	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
872		1179	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	1180	when your channel for JSON transfer is not 8-bit clean or the encoding
874	value was used in a numeric context or not).	1181	might be mangled in between (e.g. in mail), and works because ASCII is a
875		1182	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		1183
905	=back	1184	=back
906		1185
907		1186
		1187	=head2 JSON and ECMAscript
		1188
		1189	JSON syntax is based on how literals are represented in javascript (the
		1190	not-standardised predecessor of ECMAscript) which is presumably why it is
		1191	called "JavaScript Object Notation".
		1192
		1193	However, JSON is not a subset (and also not a superset of course) of
		1194	ECMAscript (the standard) or javascript (whatever browsers actually
		1195	implement).
		1196
		1197	If you want to use javascript's C<eval> function to "parse" JSON, you
		1198	might run into parse errors for valid JSON texts, or the resulting data
		1199	structure might not be queryable:
		1200
		1201	One of the problems is that U+2028 and U+2029 are valid characters inside
		1202	JSON strings, but are not allowed in ECMAscript string literals, so the
		1203	following Perl fragment will not output something that can be guaranteed
		1204	to be parsable by javascript's C<eval>:
		1205
		1206	use JSON::XS;
		1207
		1208	print encode_json [chr 0x2028];
		1209
		1210	The right fix for this is to use a proper JSON parser in your javascript
		1211	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1212	F<json2.js> parser).
		1213
		1214	If this is not an option, you can, as a stop-gap measure, simply encode to
		1215	ASCII-only JSON:
		1216
		1217	use JSON::XS;
		1218
		1219	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1220
		1221	Note that this will enlarge the resulting JSON text quite a bit if you
		1222	have many non-ASCII characters. You might be tempted to run some regexes
		1223	to only escape U+2028 and U+2029, e.g.:
		1224
		1225	# DO NOT USE THIS!
		1226	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1227	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1228	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1229	print $json;
		1230
		1231	Note that I<this is a bad idea>: the above only works for U+2028 and
		1232	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1233	javascript implementations, however, have issues with other characters as
		1234	well - using C<eval> naively simply I<will> cause problems.
		1235
		1236	Another problem is that some javascript implementations reserve
		1237	some property names for their own purposes (which probably makes
		1238	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1239	C<__proto__> property name for its own purposes.
		1240
		1241	If that is a problem, you could parse try to filter the resulting JSON
		1242	output for these property strings, e.g.:
		1243
		1244	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1245
		1246	This works because C<__proto__> is not valid outside of strings, so every
		1247	occurrence of C<"__proto__"\s*:> must be a string used as property name.
		1248
		1249	If you know of other incompatibilities, please let me know.
		1250
		1251
908	=head2 JSON and YAML	1252	=head2 JSON and YAML
909		1253
910	You often hear that JSON is a subset (or a close subset) of YAML. This is,	1254	You often hear that JSON is a subset of YAML. This is, however, a mass
911	however, a mass hysteria and very far from the truth. In general, there is	1255	hysteria(*) and very far from the truth (as of the time of this writing),
912	no way to configure JSON::XS to output a data structure as valid YAML.	1256	so let me state it clearly: I<in general, there is no way to configure
		1257	JSON::XS to output a data structure as valid YAML> that works in all
		1258	cases.
913		1259
914	If you really must use JSON::XS to generate YAML, you should use this	1260	If you really must use JSON::XS to generate YAML, you should use this
915	algorithm (subject to change in future versions):	1261	algorithm (subject to change in future versions):
916		1262
917	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1263	my $to_yaml = JSON::XS->new->utf8->space_after (1);
918	my $yaml = $to_yaml->encode ($ref) . "\n";	1264	my $yaml = $to_yaml->encode ($ref) . "\n";
919		1265
920	This will usually generate JSON texts that also parse as valid	1266	This will I<usually> generate JSON texts that also parse as valid
921	YAML. Please note that YAML has hardcoded limits on (simple) object key	1267	YAML. Please note that YAML has hardcoded limits on (simple) object key
922	lengths that JSON doesn't have, so you should make sure that your hash	1268	lengths that JSON doesn't have and also has different and incompatible
		1269	unicode character escape syntax, so you should make sure that your hash
923	keys are noticeably shorter than the 1024 characters YAML allows.	1270	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1271	and that you do not have characters with codepoint values outside the
		1272	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1273	sequences in strings (which JSON::XS does not I<currently> generate, but
		1274	other JSON generators might).
924		1275
925	There might be other incompatibilities that I am not aware of. In general	1276	There might be other incompatibilities that I am not aware of (or the YAML
		1277	specification has been changed yet again - it does so quite often). In
926	you should not try to generate YAML with a JSON generator or vice versa,	1278	general you should not try to generate YAML with a JSON generator or vice
927	or try to parse JSON with a YAML parser or vice versa: chances are high	1279	versa, or try to parse JSON with a YAML parser or vice versa: chances are
928	that you will run into severe interoperability problems.	1280	high that you will run into severe interoperability problems when you
		1281	least expect it.
		1282
		1283	=over 4
		1284
		1285	=item (*)
		1286
		1287	I have been pressured multiple times by Brian Ingerson (one of the
		1288	authors of the YAML specification) to remove this paragraph, despite him
		1289	acknowledging that the actual incompatibilities exist. As I was personally
		1290	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1291	educate people about these issues, so others do not run into the same
		1292	problem again and again. After this, Brian called me a (quote)I<complete
		1293	and worthless idiot>(unquote).
		1294
		1295	In my opinion, instead of pressuring and insulting people who actually
		1296	clarify issues with YAML and the wrong statements of some of its
		1297	proponents, I would kindly suggest reading the JSON spec (which is not
		1298	that difficult or long) and finally make YAML compatible to it, and
		1299	educating users about the changes, instead of spreading lies about the
		1300	real compatibility for many I<years> and trying to silence people who
		1301	point out that it isn't true.
		1302
		1303	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1304	though the incompatibilities have been documented (and are known to Brian)
		1305	for many years and the spec makes explicit claims that YAML is a superset
		1306	of JSON. It would be so easy to fix, but apparently, bullying people and
		1307	corrupting userdata is so much easier.
		1308
		1309	=back
929		1310
930		1311
931	=head2 SPEED	1312	=head2 SPEED
932		1313
933	It seems that JSON::XS is surprisingly fast, as shown in the following	1314	It seems that JSON::XS is surprisingly fast, as shown in the following
934	tables. They have been generated with the help of the C<eg/bench> program	1315	tables. They have been generated with the help of the C<eg/bench> program
935	in the JSON::XS distribution, to make it easy to compare on your own	1316	in the JSON::XS distribution, to make it easy to compare on your own
936	system.	1317	system.
937		1318
938	First comes a comparison between various modules using a very short	1319	First comes a comparison between various modules using
939	single-line JSON string:	1320	a very short single-line JSON string (also available at
		1321	L<http://dist.schmorp.de/misc/json/short.json>).
940		1322
941	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1323	{"method": "handleMessage", "params": ["user1",
942	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1324	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1325	1, 0]}
943		1326
944	It shows the number of encodes/decodes per second (JSON::XS uses	1327	It shows the number of encodes/decodes per second (JSON::XS uses
945	the functional interface, while JSON::XS/2 uses the OO interface	1328	the functional interface, while JSON::XS/2 uses the OO interface
946	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1329	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
947	shrink). Higher is better:	1330	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1331	uses the from_json method). Higher is better:
948		1332
949	module \| encode \| decode \|	1333	module \| encode \| decode \|
950	-----------\|------------\|------------\|	1334	--------------\|------------\|------------\|
951	JSON 1.x \| 4990.842 \| 4088.813 \|	1335	JSON::DWIW/DS \| 86302.551 \| 102300.098 \|
952	JSON::DWIW \| 51653.990 \| 71575.154 \|	1336	JSON::DWIW/FJ \| 86302.551 \| 75983.768 \|
953	JSON::PC \| 65948.176 \| 74631.744 \|	1337	JSON::PP \| 15827.562 \| 6638.658 \|
954	JSON::PP \| 8931.652 \| 3817.168 \|	1338	JSON::Syck \| 63358.066 \| 47662.545 \|
955	JSON::Syck \| 24877.248 \| 27776.848 \|	1339	JSON::XS \| 511500.488 \| 511500.488 \|
956	JSON::XS \| 388361.481 \| 227951.304 \|	1340	JSON::XS/2 \| 291271.111 \| 388361.481 \|
957	JSON::XS/2 \| 227951.304 \| 218453.333 \|	1341	JSON::XS/3 \| 361577.931 \| 361577.931 \|
958	JSON::XS/3 \| 338250.323 \| 218453.333 \|	1342	Storable \| 66788.280 \| 265462.278 \|
959	Storable \| 16500.016 \| 135300.129 \|
960	-----------+------------+------------+	1343	--------------+------------+------------+
961		1344
962	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,	1345	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
963	about three times faster on decoding, and over forty times faster	1346	about five times faster on decoding, and over thirty to seventy times
964	than JSON, even with pretty-printing and key sorting. It also compares	1347	faster than JSON's pure perl implementation. It also compares favourably
965	favourably to Storable for small amounts of data.	1348	to Storable for small amounts of data.
966		1349
967	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1350	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
968	search API (http://nanoref.com/yahooapis/mgPdGg):	1351	search API (L<http://dist.schmorp.de/misc/json/long.json>).
969		1352
970	module \| encode \| decode \|	1353	module \| encode \| decode \|
971	-----------\|------------\|------------\|	1354	--------------\|------------\|------------\|
972	JSON 1.x \| 55.260 \| 34.971 \|	1355	JSON::DWIW/DS \| 1647.927 \| 2673.916 \|
973	JSON::DWIW \| 825.228 \| 1082.513 \|	1356	JSON::DWIW/FJ \| 1630.249 \| 2596.128 \|
974	JSON::PC \| 3571.444 \| 2394.829 \|
975	JSON::PP \| 210.987 \| 32.574 \|	1357	JSON::PP \| 400.640 \| 62.311 \|
976	JSON::Syck \| 552.551 \| 787.544 \|	1358	JSON::Syck \| 1481.040 \| 1524.869 \|
977	JSON::XS \| 5780.463 \| 4854.519 \|	1359	JSON::XS \| 20661.596 \| 9541.183 \|
978	JSON::XS/2 \| 3869.998 \| 4798.975 \|	1360	JSON::XS/2 \| 10683.403 \| 9416.938 \|
979	JSON::XS/3 \| 5862.880 \| 4798.975 \|	1361	JSON::XS/3 \| 20661.596 \| 9400.054 \|
980	Storable \| 4445.002 \| 5235.027 \|	1362	Storable \| 19765.806 \| 10000.725 \|
981	-----------+------------+------------+	1363	--------------+------------+------------+
982		1364
983	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1365	Again, JSON::XS leads by far (except for Storable which non-surprisingly
984	decodes faster).	1366	decodes a bit faster).
985		1367
986	On large strings containing lots of high Unicode characters, some modules	1368	On large strings containing lots of high Unicode characters, some modules
987	(such as JSON::PC) seem to decode faster than JSON::XS, but the result	1369	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
988	will be broken due to missing (or wrong) Unicode handling. Others refuse	1370	will be broken due to missing (or wrong) Unicode handling. Others refuse
989	to decode or encode properly, so it was impossible to prepare a fair	1371	to decode or encode properly, so it was impossible to prepare a fair
…		…
1015	to free the temporary). If that is exceeded, the program crashes. To be	1397	to free the temporary). If that is exceeded, the program crashes. To be
1016	conservative, the default nesting limit is set to 512. If your process	1398	conservative, the default nesting limit is set to 512. If your process
1017	has a smaller stack, you should adjust this setting accordingly with the	1399	has a smaller stack, you should adjust this setting accordingly with the
1018	C<max_depth> method.	1400	C<max_depth> method.
1019		1401
1020	And last but least, something else could bomb you that I forgot to think	1402	Something else could bomb you, too, that I forgot to think of. In that
1021	of. In that case, you get to keep the pieces. I am always open for hints,	1403	case, you get to keep the pieces. I am always open for hints, though...
1022	though...	1404
		1405	Also keep in mind that JSON::XS might leak contents of your Perl data
		1406	structures in its error messages, so when you serialise sensitive
		1407	information you might want to make sure that exceptions thrown by JSON::XS
		1408	will not end up in front of untrusted eyes.
1023		1409
1024	If you are using JSON::XS to return packets to consumption	1410	If you are using JSON::XS to return packets to consumption
1025	by JavaScript scripts in a browser you should have a look at	1411	by JavaScript scripts in a browser you should have a look at
1026	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether	1412	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
1027	you are vulnerable to some common attack vectors (which really are browser	1413	see whether you are vulnerable to some common attack vectors (which really
1028	design bugs, but it is still you who will have to deal with it, as major	1414	are browser design bugs, but it is still you who will have to deal with
1029	browser developers care only for features, not about getting security	1415	it, as major browser developers care only for features, not about getting
1030	right).	1416	security right).
		1417
		1418
		1419	=head1 INTEROPERABILITY WITH OTHER MODULES
		1420
		1421	C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean
		1422	constants. That means that the JSON true and false values will be
		1423	comaptible to true and false values of iother modules that do the same,
		1424	such as L<JSON::PP> and L<CBOR::XS>.
1031		1425
1032		1426
1033	=head1 THREADS	1427	=head1 THREADS
1034		1428
1035	This module is I<not> guaranteed to be thread safe and there are no	1429	This module is I<not> guaranteed to be thread safe and there are no
1036	plans to change this until Perl gets thread support (as opposed to the	1430	plans to change this until Perl gets thread support (as opposed to the
1037	horribly slow so-called "threads" which are simply slow and bloated	1431	horribly slow so-called "threads" which are simply slow and bloated
1038	process simulations - use fork, its I<much> faster, cheaper, better).	1432	process simulations - use fork, it's I<much> faster, cheaper, better).
1039		1433
1040	(It might actually work, but you have been warned).	1434	(It might actually work, but you have been warned).
1041		1435
1042		1436
		1437	=head1 THE PERILS OF SETLOCALE
		1438
		1439	Sometimes people avoid the Perl locale support and directly call the
		1440	system's setlocale function with C<LC_ALL>.
		1441
		1442	This breaks both perl and modules such as JSON::XS, as stringification of
		1443	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1444	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1445	perl to stringify numbers).
		1446
		1447	The solution is simple: don't call C<setlocale>, or use it for only those
		1448	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1449
		1450	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1451	actually needs it (avoiding stringification of numbers), and restore it
		1452	afterwards.
		1453
		1454
1043	=head1 BUGS	1455	=head1 BUGS
1044		1456
1045	While the goal of this module is to be correct, that unfortunately does	1457	While the goal of this module is to be correct, that unfortunately does
1046	not mean its bug-free, only that I think its design is bug-free. It is	1458	not mean it's bug-free, only that I think its design is bug-free. If you
1047	still relatively early in its development. If you keep reporting bugs they	1459	keep reporting bugs they will be fixed swiftly, though.
1048	will be fixed swiftly, though.
1049		1460
1050	Please refrain from using rt.cpan.org or any other bug reporting	1461	Please refrain from using rt.cpan.org or any other bug reporting
1051	service. I put the contact address into my modules for a reason.	1462	service. I put the contact address into my modules for a reason.
1052		1463
1053	=cut	1464	=cut
1054		1465
1055	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };	1466	BEGIN {
1056	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };	1467	*true = \$Types::Serialiser::true;
		1468	*true = \&Types::Serialiser::true;
		1469	*false = \$Types::Serialiser::false;
		1470	*false = \&Types::Serialiser::false;
		1471	*is_bool = \&Types::Serialiser::is_bool;
1057		1472
1058	sub true() { $true }	1473	JSON::XS::Boolean:: = Types::Serialiser::Boolean::;
1059	sub false() { $false }
1060
1061	sub is_bool($) {
1062	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
1063	# or UNIVERSAL::isa $_[0], "JSON::Literal"
1064	}	1474	}
1065		1475
1066	XSLoader::load "JSON::XS", $VERSION;	1476	XSLoader::load "JSON::XS", $VERSION;
1067		1477
1068	package JSON::XS::Boolean;	1478	=head1 SEE ALSO
1069		1479
1070	use overload	1480	The F<json_xs> command line utility for quick experiments.
1071	"0+" => sub { ${$_[0]} },
1072	"++" => sub { $_[0] = ${$_[0]} + 1 },
1073	"--" => sub { $_[0] = ${$_[0]} - 1 },
1074	fallback => 1;
1075
1076	1;
1077		1481
1078	=head1 AUTHOR	1482	=head1 AUTHOR
1079		1483
1080	Marc Lehmann <schmorp@schmorp.de>	1484	Marc Lehmann <schmorp@schmorp.de>
1081	http://home.schmorp.de/	1485	http://home.schmorp.de/
1082		1486
1083	=cut	1487	=cut
1084		1488
		1489	1
		1490

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Comparing JSON-XS/XS.pm (file contents): Revision 1.79 by root, Wed Dec 19 11:42:52 2007 UTC vs. Revision 1.144 by root, Mon Oct 28 23:19:54 2013 UTC

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Comparing JSON-XS/XS.pm (file contents):
Revision 1.79 by root, Wed Dec 19 11:42:52 2007 UTC vs.
Revision 1.144 by root, Mon Oct 28 23:19:54 2013 UTC