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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.80 by root, Sat Dec 29 17:22:39 2007 UTC vs.
Revision 1.145 by root, Tue Oct 29 00:06:40 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 $VERSION = '3.0';
106	our @ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
107		108
108	our @EXPORT = qw(encode_json decode_json to_json from_json);	109	our @EXPORT = qw(encode_json decode_json);
109
110	sub to_json($) {
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.
		990
		991	=item shell-style comments (C<< # I<text> >>)
		992
		993	As a nonstandard extension to the JSON syntax that is enabled by the
		994	C<relaxed> setting, shell-style comments are allowed. They can start
		995	anywhere outside strings and go till the end of the line.
		996
		997	=item tagged values (C<< (I<tag>)I<value> >>).
		998
		999	Another nonstandard extension to the JSON syntax, enabled with the
		1000	C<allow_tags> setting, are tagged values. In this implementation, the
		1001	I<tag> must be a perl package/class name encoded as a JSON string, and the
		1002	I<value> must be a JSON array encoding optional constructor arguments.
		1003
		1004	See "OBJECT SERIALISATION", below, for details.
735		1005
736	=back	1006	=back
737		1007
738		1008
739	=head2 PERL -> JSON	1009	=head2 PERL -> JSON
…		…
744		1014
745	=over 4	1015	=over 4
746		1016
747	=item hash references	1017	=item hash references
748		1018
749	Perl hash references become JSON objects. As there is no inherent ordering	1019	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	1020	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	1021	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	1022	(determined by the I<canonical> flag), so the same datastructure will
753	optionally sort the hash keys (determined by the I<canonical> flag), so	1023	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	1024	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	1025	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		1026
759	=item array references	1027	=item array references
760		1028
761	Perl array references become JSON arrays.	1029	Perl array references become JSON arrays.
762		1030
763	=item other references	1031	=item other references
764		1032
765	Other unblessed references are generally not allowed and will cause an	1033	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	1034	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	1035	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		1036
		1037	Since C<JSON::XS> uses the boolean model from L<Types::Serialiser>, you
		1038	can also C<use Types::Serialiser> and then use C<Types::Serialiser::false>
		1039	and C<Types::Serialiser::true> to improve readability.
		1040
		1041	use Types::Serialiser;
770	encode_json [\0,JSON::XS::true] # yields [false,true]	1042	encode_json [\0, Types::Serialiser::true] # yields [false,true]
771		1043
772	=item JSON::XS::true, JSON::XS::false	1044	=item Types::Serialiser::true, Types::Serialiser::false
773		1045
774	These special values become JSON true and JSON false values,	1046	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.	1047	and JSON false values, respectively. You can also use C<\1> and C<\0>
		1048	directly if you want.
776		1049
777	=item blessed objects	1050	=item blessed objects
778		1051
779	Blessed objects are not allowed. JSON::XS currently tries to encode their	1052	Blessed objects are not directly representable in JSON, but C<JSON::XS>
780	underlying representation (hash- or arrayref), but this behaviour might	1053	allows various ways of handling objects. See "OBJECT SERIALISATION",
781	change in future versions.	1054	below, for details.
782		1055
783	=item simple scalars	1056	=item simple scalars
784		1057
785	Simple Perl scalars (any scalar that is not a reference) are the most	1058	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	1059	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	1060	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:	1061	before encoding as JSON strings, and anything else as number value:
789		1062
790	# dump as number	1063	# dump as number
791	encode_json [2] # yields [2]	1064	encode_json [2] # yields [2]
792	encode_json [-3.0e17] # yields [-3e+17]	1065	encode_json [-3.0e17] # yields [-3e+17]
793	my $value = 5; encode_json [$value] # yields [5]	1066	my $value = 5; encode_json [$value] # yields [5]
…		…
811	my $x = "3"; # some variable containing a string	1084	my $x = "3"; # some variable containing a string
812	$x += 0; # numify it, ensuring it will be dumped as a number	1085	$x += 0; # numify it, ensuring it will be dumped as a number
813	$x *= 1; # same thing, the choice is yours.	1086	$x *= 1; # same thing, the choice is yours.
814		1087
815	You can not currently force the type in other, less obscure, ways. Tell me	1088	You can not currently force the type in other, less obscure, ways. Tell me
816	if you need this capability.	1089	if you need this capability (but don't forget to explain why it's needed
		1090	:).
		1091
		1092	Note that numerical precision has the same meaning as under Perl (so
		1093	binary to decimal conversion follows the same rules as in Perl, which
		1094	can differ to other languages). Also, your perl interpreter might expose
		1095	extensions to the floating point numbers of your platform, such as
		1096	infinities or NaN's - these cannot be represented in JSON, and it is an
		1097	error to pass those in.
817		1098
818	=back	1099	=back
819		1100
		1101	=head2 OBJECT SERIALISATION
820		1102
821	=head1 COMPARISON	1103	As JSON cannot directly represent Perl objects, you have to choose between
		1104	a pure JSON representation (without the ability to deserialise the object
		1105	automatically again), and a nonstandard extension to the JSON syntax,
		1106	tagged values.
822		1107
823	As already mentioned, this module was created because none of the existing	1108	=head3 SERIALISATION
824	JSON modules could be made to work correctly. First I will describe the	1109
825	problems (or pleasures) I encountered with various existing JSON modules,	1110	What happens when C<JSON::XS> encounters a Perl object depends on the
826	followed by some benchmark values. JSON::XS was designed not to suffer	1111	C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are
827	from any of these problems or limitations.	1112	used in this order:
828		1113
829	=over 4	1114	=over 4
830		1115
831	=item JSON 1.07	1116	=item 1. C<allow_tags> is enabled and object has a C<FREEZE> method.
832		1117
833	Slow (but very portable, as it is written in pure Perl).	1118	In this case, C<JSON::XS> uses the L<Types::Serialiser> object
		1119	serialisation protocol to create a tagged JSON value, using a nonstandard
		1120	extension to the JSON syntax.
834		1121
835	Undocumented/buggy Unicode handling (how JSON handles Unicode values is	1122	This works by invoking the C<FREEZE> method on the object, with the first
836	undocumented. One can get far by feeding it Unicode strings and doing	1123	argument being the object to serialise, and the second argument being the
837	en-/decoding oneself, but Unicode escapes are not working properly).	1124	constant string C<JSON> to distinguish it from other serialisers.
838		1125
839	No round-tripping (strings get clobbered if they look like numbers, e.g.	1126	The C<FREEZE> method can return any number of values (i.e. zero or
840	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	1127	more). These values and the paclkage/classname of the object will then be
841	decode into the number 2.	1128	encoded as a tagged JSON value in the following format:
842		1129
843	=item JSON::PC 0.01	1130	("classname")[FREEZE return values...]
844		1131
845	Very fast.	1132	For example, the hypothetical C<My::Object> C<FREEZE> method might use the
		1133	objects C<type> and C<id> members to encode the object:
846		1134
847	Undocumented/buggy Unicode handling.	1135	sub My::Object::FREEZE {
		1136	my ($self, $serialiser) = @_;
848		1137
849	No round-tripping.	1138	($self->{type}, $self->{id})
		1139	}
850		1140
851	Has problems handling many Perl values (e.g. regex results and other magic	1141	=item 2. C<convert_blessed> is enabled and object has a C<TO_JSON> method.
852	values will make it croak).
853		1142
854	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1143	In this case, the C<TO_JSON> method of the object is invoked in scalar
855	which is not a valid JSON text.	1144	context. It must return a single scalar that can be directly encoded into
		1145	JSON. This scalar replaces the object in the JSON text.
856		1146
857	Unmaintained (maintainer unresponsive for many months, bugs are not	1147	For example, the following C<TO_JSON> method will convert all L<URI>
858	getting fixed).	1148	objects to JSON strings when serialised. The fatc that these values
		1149	originally were L<URI> objects is lost.
859		1150
860	=item JSON::Syck 0.21	1151	sub URI::TO_JSON {
		1152	my ($uri) = @_;
		1153	$uri->as_string
		1154	}
861		1155
862	Very buggy (often crashes).	1156	=item 3. C<allow_blessed> is enabled.
863		1157
864	Very inflexible (no human-readable format supported, format pretty much	1158	The object will be serialised as a JSON null value.
865	undocumented. I need at least a format for easy reading by humans and a
866	single-line compact format for use in a protocol, and preferably a way to
867	generate ASCII-only JSON texts).
868		1159
869	Completely broken (and confusingly documented) Unicode handling (Unicode	1160	=item 4. none of the above
870	escapes are not working properly, you need to set ImplicitUnicode to
871	I<different> values on en- and decoding to get symmetric behaviour).
872		1161
873	No round-tripping (simple cases work, but this depends on whether the scalar	1162	If none of the settings are enabled or the respective methods are missing,
874	value was used in a numeric context or not).	1163	C<JSON::XS> throws an exception.
875
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		1164
905	=back	1165	=back
906		1166
		1167	=head3 DESERIALISATION
		1168
		1169	For deserialisation there are only two cases to consider: either
		1170	nonstandard tagging was used, in which case C<allow_tags> decides,
		1171	or objects cannot be automatically be deserialised, in which
		1172	case you can use postprocessing or the C<filter_json_object> or
		1173	C<filter_json_single_key_object> callbacks to get some real objects our of
		1174	your JSON.
		1175
		1176	This section only considers the tagged value case: I a tagged JSON object
		1177	is encountered during decoding and C<allow_tags> is disabled, a parse
		1178	error will result (as if tagged values were not part of the grammar).
		1179
		1180	If C<allow_tags> is enabled, C<JSON::XS> will look up the C<THAW> method
		1181	of the package/classname used during serialisation. If there is no such
		1182	method, the decoding will fail with an error.
		1183
		1184	Otherwise, the C<THAW> method is invoked with the classname as first
		1185	argument, the constant string C<JSON> as second argument, and all the
		1186	values from the JSON array (the values originally returned by the
		1187	C<FREEZE> method) as remaining arguments.
		1188
		1189	The method must then return the object. While technically you can return
		1190	any Perl scalar, you might have to enable the C<enable_nonref> setting to
		1191	make that work in all cases, so better return an actual blessed reference.
		1192
		1193	As an example, let's implement a C<THAW> function that regenerates the
		1194	C<My::Object> from the C<FREEZE> example earlier:
		1195
		1196	sub My::Object::THAW {
		1197	my ($class, $serialiser, $type, $id) = @_;
		1198
		1199	$class->new (type => $type, id => $id)
		1200	}
		1201
		1202
		1203	=head1 ENCODING/CODESET FLAG NOTES
		1204
		1205	The interested reader might have seen a number of flags that signify
		1206	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1207	some confusion on what these do, so here is a short comparison:
		1208
		1209	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1210	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1211	control whether C<encode> escapes character values outside their respective
		1212	codeset range. Neither of these flags conflict with each other, although
		1213	some combinations make less sense than others.
		1214
		1215	Care has been taken to make all flags symmetrical with respect to
		1216	C<encode> and C<decode>, that is, texts encoded with any combination of
		1217	these flag values will be correctly decoded when the same flags are used
		1218	- in general, if you use different flag settings while encoding vs. when
		1219	decoding you likely have a bug somewhere.
		1220
		1221	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1222	simply an abstract set of character-codepoint pairs, while an encoding
		1223	takes those codepoint numbers and I<encodes> them, in our case into
		1224	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1225	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1226	the same time, which can be confusing.
		1227
		1228	=over 4
		1229
		1230	=item C<utf8> flag disabled
		1231
		1232	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1233	and expect Unicode strings, that is, characters with high ordinal Unicode
		1234	values (> 255) will be encoded as such characters, and likewise such
		1235	characters are decoded as-is, no changes to them will be done, except
		1236	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1237	respectively (to Perl, these are the same thing in strings unless you do
		1238	funny/weird/dumb stuff).
		1239
		1240	This is useful when you want to do the encoding yourself (e.g. when you
		1241	want to have UTF-16 encoded JSON texts) or when some other layer does
		1242	the encoding for you (for example, when printing to a terminal using a
		1243	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1244	to UTF-8 encode your data first and have Perl encode it another time).
		1245
		1246	=item C<utf8> flag enabled
		1247
		1248	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1249	characters using the corresponding UTF-8 multi-byte sequence, and will
		1250	expect your input strings to be encoded as UTF-8, that is, no "character"
		1251	of the input string must have any value > 255, as UTF-8 does not allow
		1252	that.
		1253
		1254	The C<utf8> flag therefore switches between two modes: disabled means you
		1255	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1256	octet/binary string in Perl.
		1257
		1258	=item C<latin1> or C<ascii> flags enabled
		1259
		1260	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1261	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1262	characters as specified by the C<utf8> flag.
		1263
		1264	If C<utf8> is disabled, then the result is also correctly encoded in those
		1265	character sets (as both are proper subsets of Unicode, meaning that a
		1266	Unicode string with all character values < 256 is the same thing as a
		1267	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1268	the same thing as an ASCII string in Perl).
		1269
		1270	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1271	regardless of these flags, just some more characters will be escaped using
		1272	C<\uXXXX> then before.
		1273
		1274	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1275	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1276	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1277	a subset of Unicode), while ASCII is.
		1278
		1279	Surprisingly, C<decode> will ignore these flags and so treat all input
		1280	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1281	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1282	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1283
		1284	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1285	they only govern when the JSON output engine escapes a character or not.
		1286
		1287	The main use for C<latin1> is to relatively efficiently store binary data
		1288	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1289
		1290	The main use for C<ascii> is to force the output to not contain characters
		1291	with values > 127, which means you can interpret the resulting string
		1292	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1293	8-bit-encoding, and still get the same data structure back. This is useful
		1294	when your channel for JSON transfer is not 8-bit clean or the encoding
		1295	might be mangled in between (e.g. in mail), and works because ASCII is a
		1296	proper subset of most 8-bit and multibyte encodings in use in the world.
		1297
		1298	=back
		1299
		1300
		1301	=head2 JSON and ECMAscript
		1302
		1303	JSON syntax is based on how literals are represented in javascript (the
		1304	not-standardised predecessor of ECMAscript) which is presumably why it is
		1305	called "JavaScript Object Notation".
		1306
		1307	However, JSON is not a subset (and also not a superset of course) of
		1308	ECMAscript (the standard) or javascript (whatever browsers actually
		1309	implement).
		1310
		1311	If you want to use javascript's C<eval> function to "parse" JSON, you
		1312	might run into parse errors for valid JSON texts, or the resulting data
		1313	structure might not be queryable:
		1314
		1315	One of the problems is that U+2028 and U+2029 are valid characters inside
		1316	JSON strings, but are not allowed in ECMAscript string literals, so the
		1317	following Perl fragment will not output something that can be guaranteed
		1318	to be parsable by javascript's C<eval>:
		1319
		1320	use JSON::XS;
		1321
		1322	print encode_json [chr 0x2028];
		1323
		1324	The right fix for this is to use a proper JSON parser in your javascript
		1325	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1326	F<json2.js> parser).
		1327
		1328	If this is not an option, you can, as a stop-gap measure, simply encode to
		1329	ASCII-only JSON:
		1330
		1331	use JSON::XS;
		1332
		1333	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1334
		1335	Note that this will enlarge the resulting JSON text quite a bit if you
		1336	have many non-ASCII characters. You might be tempted to run some regexes
		1337	to only escape U+2028 and U+2029, e.g.:
		1338
		1339	# DO NOT USE THIS!
		1340	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1341	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1342	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1343	print $json;
		1344
		1345	Note that I<this is a bad idea>: the above only works for U+2028 and
		1346	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1347	javascript implementations, however, have issues with other characters as
		1348	well - using C<eval> naively simply I<will> cause problems.
		1349
		1350	Another problem is that some javascript implementations reserve
		1351	some property names for their own purposes (which probably makes
		1352	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1353	C<__proto__> property name for its own purposes.
		1354
		1355	If that is a problem, you could parse try to filter the resulting JSON
		1356	output for these property strings, e.g.:
		1357
		1358	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1359
		1360	This works because C<__proto__> is not valid outside of strings, so every
		1361	occurrence of C<"__proto__"\s*:> must be a string used as property name.
		1362
		1363	If you know of other incompatibilities, please let me know.
		1364
907		1365
908	=head2 JSON and YAML	1366	=head2 JSON and YAML
909		1367
910	You often hear that JSON is a subset of YAML. This is, however, a mass	1368	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	1369	hysteria(*) and very far from the truth (as of the time of this writing),
		1370	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	1371	JSON::XS to output a data structure as valid YAML> that works in all
913	all cases.	1372	cases.
914		1373
915	If you really must use JSON::XS to generate YAML, you should use this	1374	If you really must use JSON::XS to generate YAML, you should use this
916	algorithm (subject to change in future versions):	1375	algorithm (subject to change in future versions):
917		1376
918	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1377	my $to_yaml = JSON::XS->new->utf8->space_after (1);
919	my $yaml = $to_yaml->encode ($ref) . "\n";	1378	my $yaml = $to_yaml->encode ($ref) . "\n";
920		1379
921	This will usually generate JSON texts that also parse as valid	1380	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	1381	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	1382	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	1383	unicode character escape syntax, so you should make sure that your hash
925	noticeably shorter than the 1024 "stream characters" YAML allows and that	1384	keys are noticeably shorter than the 1024 "stream characters" YAML allows
926	you do not have codepoints with values outside the Unicode BMP (basic	1385	and that you do not have characters with codepoint values outside the
927	multilingual page).	1386	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1387	sequences in strings (which JSON::XS does not I<currently> generate, but
		1388	other JSON generators might).
928		1389
929	There might be other incompatibilities that I am not aware of. In general	1390	There might be other incompatibilities that I am not aware of (or the YAML
		1391	specification has been changed yet again - it does so quite often). In
930	you should not try to generate YAML with a JSON generator or vice versa,	1392	general you should not try to generate YAML with a JSON generator or vice
931	or try to parse JSON with a YAML parser or vice versa: chances are high	1393	versa, or try to parse JSON with a YAML parser or vice versa: chances are
932	that you will run into severe interoperability problems when you least	1394	high that you will run into severe interoperability problems when you
933	expect it.	1395	least expect it.
		1396
		1397	=over 4
		1398
		1399	=item (*)
		1400
		1401	I have been pressured multiple times by Brian Ingerson (one of the
		1402	authors of the YAML specification) to remove this paragraph, despite him
		1403	acknowledging that the actual incompatibilities exist. As I was personally
		1404	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1405	educate people about these issues, so others do not run into the same
		1406	problem again and again. After this, Brian called me a (quote)I<complete
		1407	and worthless idiot>(unquote).
		1408
		1409	In my opinion, instead of pressuring and insulting people who actually
		1410	clarify issues with YAML and the wrong statements of some of its
		1411	proponents, I would kindly suggest reading the JSON spec (which is not
		1412	that difficult or long) and finally make YAML compatible to it, and
		1413	educating users about the changes, instead of spreading lies about the
		1414	real compatibility for many I<years> and trying to silence people who
		1415	point out that it isn't true.
		1416
		1417	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1418	though the incompatibilities have been documented (and are known to Brian)
		1419	for many years and the spec makes explicit claims that YAML is a superset
		1420	of JSON. It would be so easy to fix, but apparently, bullying people and
		1421	corrupting userdata is so much easier.
		1422
		1423	=back
934		1424
935		1425
936	=head2 SPEED	1426	=head2 SPEED
937		1427
938	It seems that JSON::XS is surprisingly fast, as shown in the following	1428	It seems that JSON::XS is surprisingly fast, as shown in the following
939	tables. They have been generated with the help of the C<eg/bench> program	1429	tables. They have been generated with the help of the C<eg/bench> program
940	in the JSON::XS distribution, to make it easy to compare on your own	1430	in the JSON::XS distribution, to make it easy to compare on your own
941	system.	1431	system.
942		1432
943	First comes a comparison between various modules using a very short	1433	First comes a comparison between various modules using
944	single-line JSON string:	1434	a very short single-line JSON string (also available at
		1435	L<http://dist.schmorp.de/misc/json/short.json>).
945		1436
946	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1437	{"method": "handleMessage", "params": ["user1",
947	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1438	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1439	1, 0]}
948		1440
949	It shows the number of encodes/decodes per second (JSON::XS uses	1441	It shows the number of encodes/decodes per second (JSON::XS uses
950	the functional interface, while JSON::XS/2 uses the OO interface	1442	the functional interface, while JSON::XS/2 uses the OO interface
951	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1443	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
952	shrink). Higher is better:	1444	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1445	uses the from_json method). Higher is better:
953		1446
954	module \| encode \| decode \|	1447	module \| encode \| decode \|
955	-----------\|------------\|------------\|	1448	--------------\|------------\|------------\|
956	JSON 1.x \| 4990.842 \| 4088.813 \|	1449	JSON::DWIW/DS \| 86302.551 \| 102300.098 \|
957	JSON::DWIW \| 51653.990 \| 71575.154 \|	1450	JSON::DWIW/FJ \| 86302.551 \| 75983.768 \|
958	JSON::PC \| 65948.176 \| 74631.744 \|	1451	JSON::PP \| 15827.562 \| 6638.658 \|
959	JSON::PP \| 8931.652 \| 3817.168 \|	1452	JSON::Syck \| 63358.066 \| 47662.545 \|
960	JSON::Syck \| 24877.248 \| 27776.848 \|	1453	JSON::XS \| 511500.488 \| 511500.488 \|
961	JSON::XS \| 388361.481 \| 227951.304 \|	1454	JSON::XS/2 \| 291271.111 \| 388361.481 \|
962	JSON::XS/2 \| 227951.304 \| 218453.333 \|	1455	JSON::XS/3 \| 361577.931 \| 361577.931 \|
963	JSON::XS/3 \| 338250.323 \| 218453.333 \|	1456	Storable \| 66788.280 \| 265462.278 \|
964	Storable \| 16500.016 \| 135300.129 \|
965	-----------+------------+------------+	1457	--------------+------------+------------+
966		1458
967	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,	1459	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
968	about three times faster on decoding, and over forty times faster	1460	about five times faster on decoding, and over thirty to seventy times
969	than JSON, even with pretty-printing and key sorting. It also compares	1461	faster than JSON's pure perl implementation. It also compares favourably
970	favourably to Storable for small amounts of data.	1462	to Storable for small amounts of data.
971		1463
972	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1464	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
973	search API (http://nanoref.com/yahooapis/mgPdGg):	1465	search API (L<http://dist.schmorp.de/misc/json/long.json>).
974		1466
975	module \| encode \| decode \|	1467	module \| encode \| decode \|
976	-----------\|------------\|------------\|	1468	--------------\|------------\|------------\|
977	JSON 1.x \| 55.260 \| 34.971 \|	1469	JSON::DWIW/DS \| 1647.927 \| 2673.916 \|
978	JSON::DWIW \| 825.228 \| 1082.513 \|	1470	JSON::DWIW/FJ \| 1630.249 \| 2596.128 \|
979	JSON::PC \| 3571.444 \| 2394.829 \|
980	JSON::PP \| 210.987 \| 32.574 \|	1471	JSON::PP \| 400.640 \| 62.311 \|
981	JSON::Syck \| 552.551 \| 787.544 \|	1472	JSON::Syck \| 1481.040 \| 1524.869 \|
982	JSON::XS \| 5780.463 \| 4854.519 \|	1473	JSON::XS \| 20661.596 \| 9541.183 \|
983	JSON::XS/2 \| 3869.998 \| 4798.975 \|	1474	JSON::XS/2 \| 10683.403 \| 9416.938 \|
984	JSON::XS/3 \| 5862.880 \| 4798.975 \|	1475	JSON::XS/3 \| 20661.596 \| 9400.054 \|
985	Storable \| 4445.002 \| 5235.027 \|	1476	Storable \| 19765.806 \| 10000.725 \|
986	-----------+------------+------------+	1477	--------------+------------+------------+
987		1478
988	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1479	Again, JSON::XS leads by far (except for Storable which non-surprisingly
989	decodes faster).	1480	decodes a bit faster).
990		1481
991	On large strings containing lots of high Unicode characters, some modules	1482	On large strings containing lots of high Unicode characters, some modules
992	(such as JSON::PC) seem to decode faster than JSON::XS, but the result	1483	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
993	will be broken due to missing (or wrong) Unicode handling. Others refuse	1484	will be broken due to missing (or wrong) Unicode handling. Others refuse
994	to decode or encode properly, so it was impossible to prepare a fair	1485	to decode or encode properly, so it was impossible to prepare a fair
…		…
1020	to free the temporary). If that is exceeded, the program crashes. To be	1511	to free the temporary). If that is exceeded, the program crashes. To be
1021	conservative, the default nesting limit is set to 512. If your process	1512	conservative, the default nesting limit is set to 512. If your process
1022	has a smaller stack, you should adjust this setting accordingly with the	1513	has a smaller stack, you should adjust this setting accordingly with the
1023	C<max_depth> method.	1514	C<max_depth> method.
1024		1515
1025	And last but least, something else could bomb you that I forgot to think	1516	Something else could bomb you, too, that I forgot to think of. In that
1026	of. In that case, you get to keep the pieces. I am always open for hints,	1517	case, you get to keep the pieces. I am always open for hints, though...
1027	though...	1518
		1519	Also keep in mind that JSON::XS might leak contents of your Perl data
		1520	structures in its error messages, so when you serialise sensitive
		1521	information you might want to make sure that exceptions thrown by JSON::XS
		1522	will not end up in front of untrusted eyes.
1028		1523
1029	If you are using JSON::XS to return packets to consumption	1524	If you are using JSON::XS to return packets to consumption
1030	by JavaScript scripts in a browser you should have a look at	1525	by JavaScript scripts in a browser you should have a look at
1031	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether	1526	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
1032	you are vulnerable to some common attack vectors (which really are browser	1527	see whether you are vulnerable to some common attack vectors (which really
1033	design bugs, but it is still you who will have to deal with it, as major	1528	are browser design bugs, but it is still you who will have to deal with
1034	browser developers care only for features, not about getting security	1529	it, as major browser developers care only for features, not about getting
1035	right).	1530	security right).
		1531
		1532
		1533	=head1 INTEROPERABILITY WITH OTHER MODULES
		1534
		1535	C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean
		1536	constants. That means that the JSON true and false values will be
		1537	comaptible to true and false values of iother modules that do the same,
		1538	such as L<JSON::PP> and L<CBOR::XS>.
1036		1539
1037		1540
1038	=head1 THREADS	1541	=head1 THREADS
1039		1542
1040	This module is I<not> guaranteed to be thread safe and there are no	1543	This module is I<not> guaranteed to be thread safe and there are no
1041	plans to change this until Perl gets thread support (as opposed to the	1544	plans to change this until Perl gets thread support (as opposed to the
1042	horribly slow so-called "threads" which are simply slow and bloated	1545	horribly slow so-called "threads" which are simply slow and bloated
1043	process simulations - use fork, its I<much> faster, cheaper, better).	1546	process simulations - use fork, it's I<much> faster, cheaper, better).
1044		1547
1045	(It might actually work, but you have been warned).	1548	(It might actually work, but you have been warned).
1046		1549
1047		1550
		1551	=head1 THE PERILS OF SETLOCALE
		1552
		1553	Sometimes people avoid the Perl locale support and directly call the
		1554	system's setlocale function with C<LC_ALL>.
		1555
		1556	This breaks both perl and modules such as JSON::XS, as stringification of
		1557	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1558	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1559	perl to stringify numbers).
		1560
		1561	The solution is simple: don't call C<setlocale>, or use it for only those
		1562	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1563
		1564	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1565	actually needs it (avoiding stringification of numbers), and restore it
		1566	afterwards.
		1567
		1568
1048	=head1 BUGS	1569	=head1 BUGS
1049		1570
1050	While the goal of this module is to be correct, that unfortunately does	1571	While the goal of this module is to be correct, that unfortunately does
1051	not mean its bug-free, only that I think its design is bug-free. It is	1572	not mean it's bug-free, only that I think its design is bug-free. If you
1052	still relatively early in its development. If you keep reporting bugs they	1573	keep reporting bugs they will be fixed swiftly, though.
1053	will be fixed swiftly, though.
1054		1574
1055	Please refrain from using rt.cpan.org or any other bug reporting	1575	Please refrain from using rt.cpan.org or any other bug reporting
1056	service. I put the contact address into my modules for a reason.	1576	service. I put the contact address into my modules for a reason.
1057		1577
1058	=cut	1578	=cut
1059		1579
1060	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };	1580	BEGIN {
1061	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };	1581	*true = \$Types::Serialiser::true;
		1582	*true = \&Types::Serialiser::true;
		1583	*false = \$Types::Serialiser::false;
		1584	*false = \&Types::Serialiser::false;
		1585	*is_bool = \&Types::Serialiser::is_bool;
1062		1586
1063	sub true() { $true }	1587	JSON::XS::Boolean:: = Types::Serialiser::Boolean::;
1064	sub false() { $false }
1065
1066	sub is_bool($) {
1067	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
1068	# or UNIVERSAL::isa $_[0], "JSON::Literal"
1069	}	1588	}
1070		1589
1071	XSLoader::load "JSON::XS", $VERSION;	1590	XSLoader::load "JSON::XS", $VERSION;
1072		1591
1073	package JSON::XS::Boolean;	1592	=head1 SEE ALSO
1074		1593
1075	use overload	1594	The F<json_xs> command line utility for quick experiments.
1076	"0+" => sub { ${$_[0]} },
1077	"++" => sub { $_[0] = ${$_[0]} + 1 },
1078	"--" => sub { $_[0] = ${$_[0]} - 1 },
1079	fallback => 1;
1080
1081	1;
1082		1595
1083	=head1 AUTHOR	1596	=head1 AUTHOR
1084		1597
1085	Marc Lehmann <schmorp@schmorp.de>	1598	Marc Lehmann <schmorp@schmorp.de>
1086	http://home.schmorp.de/	1599	http://home.schmorp.de/
1087		1600
1088	=cut	1601	=cut
1089		1602
		1603	1
		1604

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing JSON-XS/XS.pm (file contents): Revision 1.80 by root, Sat Dec 29 17:22:39 2007 UTC vs. Revision 1.145 by root, Tue Oct 29 00:06:40 2013 UTC

Diff Legend

Comparing JSON-XS/XS.pm (file contents):
Revision 1.80 by root, Sat Dec 29 17:22:39 2007 UTC vs.
Revision 1.145 by root, Tue Oct 29 00:06:40 2013 UTC