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Revision 1.17 by root, Sat Mar 24 19:42:14 2007 UTC vs.
Revision 1.99 by root, Thu Mar 27 06:37:35 2008 UTC

1	=head1 NAME	1	=head1 NAME
2		2
		3	=encoding utf-8
		4
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	5	JSON::XS - JSON serialising/deserialising, done correctly and fast
4		6
		7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
		8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
		9
5	=head1 SYNOPSIS	10	=head1 SYNOPSIS
6		11
7	use JSON::XS;	12	use JSON::XS;
8		13
9	# exported functions, croak on error	14	# exported functions, they croak on error
		15	# and expect/generate UTF-8
10		16
11	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
12	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
13		19
14	# oo-interface	20	# OO-interface
15		21
16	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
17	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
18	$perl_scalar = $coder->decode ($unicode_json_text);	24	$perl_scalar = $coder->decode ($unicode_json_text);
19		25
		26	# Note that JSON version 2.0 and above will automatically use JSON::XS
		27	# if available, at virtually no speed overhead either, so you should
		28	# be able to just:
		29
		30	use JSON;
		31
		32	# and do the same things, except that you have a pure-perl fallback now.
		33
20	=head1 DESCRIPTION	34	=head1 DESCRIPTION
21		35
22	This module converts Perl data structures to JSON and vice versa. Its	36	This module converts Perl data structures to JSON and vice versa. Its
23	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
24	I<fast>. To reach the latter goal it was written in C.	38	I<fast>. To reach the latter goal it was written in C.
		39
		40	Beginning with version 2.0 of the JSON module, when both JSON and
		41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
		42	overriden) with no overhead due to emulation (by inheritign constructor
		43	and methods). If JSON::XS is not available, it will fall back to the
		44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
		45	gives you a portable JSON API that can be fast when you need and doesn't
		46	require a C compiler when that is a problem.
25		47
26	As this is the n-th-something JSON module on CPAN, what was the reason	48	As this is the n-th-something JSON module on CPAN, what was the reason
27	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
28	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
29	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
…		…
36		58
37	=head2 FEATURES	59	=head2 FEATURES
38		60
39	=over 4	61	=over 4
40		62
41	=item * correct handling of unicode issues	63	=item * correct Unicode handling
42		64
43	This module knows how to handle Unicode, and even documents how and when	65	This module knows how to handle Unicode, documents how and when it does
44	it does so.	66	so, and even documents what "correct" means.
45		67
46	=item * round-trip integrity	68	=item * round-trip integrity
47		69
48	When you serialise a perl data structure using only datatypes supported	70	When you serialise a perl data structure using only datatypes supported
49	by JSON, the deserialised data structure is identical on the Perl level.	71	by JSON, the deserialised data structure is identical on the Perl level.
50	(e.g. the string "2.0" doesn't suddenly become "2").	72	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
		73	like a number). There minor I<are> exceptions to this, read the MAPPING
		74	section below to learn about those.
51		75
52	=item * strict checking of JSON correctness	76	=item * strict checking of JSON correctness
53		77
54	There is no guessing, no generating of illegal JSON texts by default,	78	There is no guessing, no generating of illegal JSON texts by default,
55	and only JSON is accepted as input by default (the latter is a security	79	and only JSON is accepted as input by default (the latter is a security
56	feature).	80	feature).
57		81
58	=item * fast	82	=item * fast
59		83
60	Compared to other JSON modules, this module compares favourably in terms	84	Compared to other JSON modules and other serialisers such as Storable,
61	of speed, too.	85	this module usually compares favourably in terms of speed, too.
62		86
63	=item * simple to use	87	=item * simple to use
64		88
65	This module has both a simple functional interface as well as an OO	89	This module has both a simple functional interface as well as an objetc
66	interface.	90	oriented interface interface.
67		91
68	=item * reasonably versatile output formats	92	=item * reasonably versatile output formats
69		93
70	You can choose between the most compact guarenteed single-line format	94	You can choose between the most compact guaranteed-single-line format
71	possible (nice for simple line-based protocols), a pure-ascii format (for	95	possible (nice for simple line-based protocols), a pure-ascii format
72	when your transport is not 8-bit clean), or a pretty-printed format (for	96	(for when your transport is not 8-bit clean, still supports the whole
73	when you want to read that stuff). Or you can combine those features in	97	Unicode range), or a pretty-printed format (for when you want to read that
74	whatever way you like.	98	stuff). Or you can combine those features in whatever way you like.
75		99
76	=back	100	=back
77		101
78	=cut	102	=cut
79		103
80	package JSON::XS;	104	package JSON::XS;
81		105
82	BEGIN {	106	use strict;
		107
83	$VERSION = '0.5';	108	our $VERSION = '2.2';
84	@ISA = qw(Exporter);	109	our @ISA = qw(Exporter);
85		110
86	@EXPORT = qw(to_json from_json);	111	our @EXPORT = qw(encode_json decode_json to_json from_json);
87	require Exporter;
88		112
		113	sub to_json($) {
89	require XSLoader;	114	require Carp;
90	XSLoader::load JSON::XS::, $VERSION;	115	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
91	}	116	}
92		117
		118	sub from_json($) {
		119	require Carp;
		120	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");
		121	}
		122
		123	use Exporter;
		124	use XSLoader;
		125
93	=head1 FUNCTIONAL INTERFACE	126	=head1 FUNCTIONAL INTERFACE
94		127
95	The following convinience methods are provided by this module. They are	128	The following convenience methods are provided by this module. They are
96	exported by default:	129	exported by default:
97		130
98	=over 4	131	=over 4
99		132
100	=item $json_text = to_json $perl_scalar	133	=item $json_text = encode_json $perl_scalar
101		134
102	Converts the given Perl data structure (a simple scalar or a reference to	135	Converts the given Perl data structure to a UTF-8 encoded, binary string
103	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	136	(that is, the string contains octets only). Croaks on error.
104	octets only). Croaks on error.
105		137
106	This function call is functionally identical to:	138	This function call is functionally identical to:
107		139
108	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	140	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
109		141
110	except being faster.	142	except being faster.
111		143
112	=item $perl_scalar = from_json $json_text	144	=item $perl_scalar = decode_json $json_text
113		145
114	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	146	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
115	parse that as an UTF-8 encoded JSON text, returning the resulting simple	147	to parse that as an UTF-8 encoded JSON text, returning the resulting
116	scalar or reference. Croaks on error.	148	reference. Croaks on error.
117		149
118	This function call is functionally identical to:	150	This function call is functionally identical to:
119		151
120	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	152	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
121		153
122	except being faster.	154	except being faster.
123		155
		156	=item $is_boolean = JSON::XS::is_bool $scalar
		157
		158	Returns true if the passed scalar represents either JSON::XS::true or
		159	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
		160	and are used to represent JSON C<true> and C<false> values in Perl.
		161
		162	See MAPPING, below, for more information on how JSON values are mapped to
		163	Perl.
		164
124	=back	165	=back
		166
		167
		168	=head1 A FEW NOTES ON UNICODE AND PERL
		169
		170	Since this often leads to confusion, here are a few very clear words on
		171	how Unicode works in Perl, modulo bugs.
		172
		173	=over 4
		174
		175	=item 1. Perl strings can store characters with ordinal values > 255.
		176
		177	This enables you to store Unicode characters as single characters in a
		178	Perl string - very natural.
		179
		180	=item 2. Perl does I<not> associate an encoding with your strings.
		181
		182	... until you force it to, e.g. when matching it against a regex, or
		183	printing the scalar to a file, in which case Perl either interprets your
		184	string as locale-encoded text, octets/binary, or as Unicode, depending
		185	on various settings. In no case is an encoding stored together with your
		186	data, it is I<use> that decides encoding, not any magical meta data.
		187
		188	=item 3. The internal utf-8 flag has no meaning with regards to the
		189	encoding of your string.
		190
		191	Just ignore that flag unless you debug a Perl bug, a module written in
		192	XS or want to dive into the internals of perl. Otherwise it will only
		193	confuse you, as, despite the name, it says nothing about how your string
		194	is encoded. You can have Unicode strings with that flag set, with that
		195	flag clear, and you can have binary data with that flag set and that flag
		196	clear. Other possibilities exist, too.
		197
		198	If you didn't know about that flag, just the better, pretend it doesn't
		199	exist.
		200
		201	=item 4. A "Unicode String" is simply a string where each character can be
		202	validly interpreted as a Unicode codepoint.
		203
		204	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		205	Unicode string encoded in UTF-8, giving you a binary string.
		206
		207	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		208
		209	It's a fact. Learn to live with it.
		210
		211	=back
		212
		213	I hope this helps :)
		214
125		215
126	=head1 OBJECT-ORIENTED INTERFACE	216	=head1 OBJECT-ORIENTED INTERFACE
127		217
128	The object oriented interface lets you configure your own encoding or	218	The object oriented interface lets you configure your own encoding or
129	decoding style, within the limits of supported formats.	219	decoding style, within the limits of supported formats.
…		…
141	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})	231	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
142	=> {"a": [1, 2]}	232	=> {"a": [1, 2]}
143		233
144	=item $json = $json->ascii ([$enable])	234	=item $json = $json->ascii ([$enable])
145		235
		236	=item $enabled = $json->get_ascii
		237
146	If C<$enable> is true (or missing), then the C<encode> method will not	238	If C<$enable> is true (or missing), then the C<encode> method will not
147	generate characters outside the code range C<0..127> (which is ASCII). Any	239	generate characters outside the code range C<0..127> (which is ASCII). Any
148	unicode characters outside that range will be escaped using either a	240	Unicode characters outside that range will be escaped using either a
149	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,	241	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
150	as per RFC4627.	242	as per RFC4627. The resulting encoded JSON text can be treated as a native
		243	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		244	or any other superset of ASCII.
151		245
152	If C<$enable> is false, then the C<encode> method will not escape Unicode	246	If C<$enable> is false, then the C<encode> method will not escape Unicode
153	characters unless required by the JSON syntax. This results in a faster	247	characters unless required by the JSON syntax or other flags. This results
154	and more compact format.	248	in a faster and more compact format.
		249
		250	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		251	document.
		252
		253	The main use for this flag is to produce JSON texts that can be
		254	transmitted over a 7-bit channel, as the encoded JSON texts will not
		255	contain any 8 bit characters.
155		256
156	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	257	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
157	=> ["\ud801\udc01"]	258	=> ["\ud801\udc01"]
158		259
		260	=item $json = $json->latin1 ([$enable])
		261
		262	=item $enabled = $json->get_latin1
		263
		264	If C<$enable> is true (or missing), then the C<encode> method will encode
		265	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		266	outside the code range C<0..255>. The resulting string can be treated as a
		267	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		268	will not be affected in any way by this flag, as C<decode> by default
		269	expects Unicode, which is a strict superset of latin1.
		270
		271	If C<$enable> is false, then the C<encode> method will not escape Unicode
		272	characters unless required by the JSON syntax or other flags.
		273
		274	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		275	document.
		276
		277	The main use for this flag is efficiently encoding binary data as JSON
		278	text, as most octets will not be escaped, resulting in a smaller encoded
		279	size. The disadvantage is that the resulting JSON text is encoded
		280	in latin1 (and must correctly be treated as such when storing and
		281	transferring), a rare encoding for JSON. It is therefore most useful when
		282	you want to store data structures known to contain binary data efficiently
		283	in files or databases, not when talking to other JSON encoders/decoders.
		284
		285	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		286	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
		287
159	=item $json = $json->utf8 ([$enable])	288	=item $json = $json->utf8 ([$enable])
		289
		290	=item $enabled = $json->get_utf8
160		291
161	If C<$enable> is true (or missing), then the C<encode> method will encode	292	If C<$enable> is true (or missing), then the C<encode> method will encode
162	the JSON result into UTF-8, as required by many protocols, while the	293	the JSON result into UTF-8, as required by many protocols, while the
163	C<decode> method expects to be handled an UTF-8-encoded string. Please	294	C<decode> method expects to be handled an UTF-8-encoded string. Please
164	note that UTF-8-encoded strings do not contain any characters outside the	295	note that UTF-8-encoded strings do not contain any characters outside the
165	range C<0..255>, they are thus useful for bytewise/binary I/O. In future	296	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
166	versions, enabling this option might enable autodetection of the UTF-16	297	versions, enabling this option might enable autodetection of the UTF-16
167	and UTF-32 encoding families, as described in RFC4627.	298	and UTF-32 encoding families, as described in RFC4627.
168		299
169	If C<$enable> is false, then the C<encode> method will return the JSON	300	If C<$enable> is false, then the C<encode> method will return the JSON
170	string as a (non-encoded) unicode string, while C<decode> expects thus a	301	string as a (non-encoded) Unicode string, while C<decode> expects thus a
171	unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	302	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
172	to be done yourself, e.g. using the Encode module.	303	to be done yourself, e.g. using the Encode module.
		304
		305	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		306	document.
173		307
174	Example, output UTF-16BE-encoded JSON:	308	Example, output UTF-16BE-encoded JSON:
175		309
176	use Encode;	310	use Encode;
177	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	311	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
198	]	332	]
199	}	333	}
200		334
201	=item $json = $json->indent ([$enable])	335	=item $json = $json->indent ([$enable])
202		336
		337	=item $enabled = $json->get_indent
		338
203	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	339	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
204	format as output, putting every array member or object/hash key-value pair	340	format as output, putting every array member or object/hash key-value pair
205	into its own line, identing them properly.	341	into its own line, indenting them properly.
206		342
207	If C<$enable> is false, no newlines or indenting will be produced, and the	343	If C<$enable> is false, no newlines or indenting will be produced, and the
208	resulting JSON text is guarenteed not to contain any C<newlines>.	344	resulting JSON text is guaranteed not to contain any C<newlines>.
209		345
210	This setting has no effect when decoding JSON texts.	346	This setting has no effect when decoding JSON texts.
211		347
212	=item $json = $json->space_before ([$enable])	348	=item $json = $json->space_before ([$enable])
		349
		350	=item $enabled = $json->get_space_before
213		351
214	If C<$enable> is true (or missing), then the C<encode> method will add an extra	352	If C<$enable> is true (or missing), then the C<encode> method will add an extra
215	optional space before the C<:> separating keys from values in JSON objects.	353	optional space before the C<:> separating keys from values in JSON objects.
216		354
217	If C<$enable> is false, then the C<encode> method will not add any extra	355	If C<$enable> is false, then the C<encode> method will not add any extra
…		…
223	Example, space_before enabled, space_after and indent disabled:	361	Example, space_before enabled, space_after and indent disabled:
224		362
225	{"key" :"value"}	363	{"key" :"value"}
226		364
227	=item $json = $json->space_after ([$enable])	365	=item $json = $json->space_after ([$enable])
		366
		367	=item $enabled = $json->get_space_after
228		368
229	If C<$enable> is true (or missing), then the C<encode> method will add an extra	369	If C<$enable> is true (or missing), then the C<encode> method will add an extra
230	optional space after the C<:> separating keys from values in JSON objects	370	optional space after the C<:> separating keys from values in JSON objects
231	and extra whitespace after the C<,> separating key-value pairs and array	371	and extra whitespace after the C<,> separating key-value pairs and array
232	members.	372	members.
…		…
238		378
239	Example, space_before and indent disabled, space_after enabled:	379	Example, space_before and indent disabled, space_after enabled:
240		380
241	{"key": "value"}	381	{"key": "value"}
242		382
		383	=item $json = $json->relaxed ([$enable])
		384
		385	=item $enabled = $json->get_relaxed
		386
		387	If C<$enable> is true (or missing), then C<decode> will accept some
		388	extensions to normal JSON syntax (see below). C<encode> will not be
		389	affected in anyway. I<Be aware that this option makes you accept invalid
		390	JSON texts as if they were valid!>. I suggest only to use this option to
		391	parse application-specific files written by humans (configuration files,
		392	resource files etc.)
		393
		394	If C<$enable> is false (the default), then C<decode> will only accept
		395	valid JSON texts.
		396
		397	Currently accepted extensions are:
		398
		399	=over 4
		400
		401	=item * list items can have an end-comma
		402
		403	JSON I<separates> array elements and key-value pairs with commas. This
		404	can be annoying if you write JSON texts manually and want to be able to
		405	quickly append elements, so this extension accepts comma at the end of
		406	such items not just between them:
		407
		408	[
		409	1,
		410	2, <- this comma not normally allowed
		411	]
		412	{
		413	"k1": "v1",
		414	"k2": "v2", <- this comma not normally allowed
		415	}
		416
		417	=item * shell-style '#'-comments
		418
		419	Whenever JSON allows whitespace, shell-style comments are additionally
		420	allowed. They are terminated by the first carriage-return or line-feed
		421	character, after which more white-space and comments are allowed.
		422
		423	[
		424	1, # this comment not allowed in JSON
		425	# neither this one...
		426	]
		427
		428	=back
		429
243	=item $json = $json->canonical ([$enable])	430	=item $json = $json->canonical ([$enable])
		431
		432	=item $enabled = $json->get_canonical
244		433
245	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	434	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
246	by sorting their keys. This is adding a comparatively high overhead.	435	by sorting their keys. This is adding a comparatively high overhead.
247		436
248	If C<$enable> is false, then the C<encode> method will output key-value	437	If C<$enable> is false, then the C<encode> method will output key-value
249	pairs in the order Perl stores them (which will likely change between runs	438	pairs in the order Perl stores them (which will likely change between runs
250	of the same script).	439	of the same script).
251		440
252	This option is useful if you want the same data structure to be encoded as	441	This option is useful if you want the same data structure to be encoded as
253	the same JSON text (given the same overall settings). If it is disabled,	442	the same JSON text (given the same overall settings). If it is disabled,
254	the same hash migh be encoded differently even if contains the same data,	443	the same hash might be encoded differently even if contains the same data,
255	as key-value pairs have no inherent ordering in Perl.	444	as key-value pairs have no inherent ordering in Perl.
256		445
257	This setting has no effect when decoding JSON texts.	446	This setting has no effect when decoding JSON texts.
258		447
259	=item $json = $json->allow_nonref ([$enable])	448	=item $json = $json->allow_nonref ([$enable])
		449
		450	=item $enabled = $json->get_allow_nonref
260		451
261	If C<$enable> is true (or missing), then the C<encode> method can convert a	452	If C<$enable> is true (or missing), then the C<encode> method can convert a
262	non-reference into its corresponding string, number or null JSON value,	453	non-reference into its corresponding string, number or null JSON value,
263	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	454	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
264	values instead of croaking.	455	values instead of croaking.
…		…
272	resulting in an invalid JSON text:	463	resulting in an invalid JSON text:
273		464
274	JSON::XS->new->allow_nonref->encode ("Hello, World!")	465	JSON::XS->new->allow_nonref->encode ("Hello, World!")
275	=> "Hello, World!"	466	=> "Hello, World!"
276		467
		468	=item $json = $json->allow_unknown ([$enable])
		469
		470	=item $enabled = $json->get_allow_unknown
		471
		472	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		473	exception when it encounters values it cannot represent in JSON (for
		474	example, filehandles) but instead will encode a JSON C<null> value. Note
		475	that blessed objects are not included here and are handled separately by
		476	c<allow_nonref>.
		477
		478	If C<$enable> is false (the default), then C<encode> will throw an
		479	exception when it encounters anything it cannot encode as JSON.
		480
		481	This option does not affect C<decode> in any way, and it is recommended to
		482	leave it off unless you know your communications partner.
		483
		484	=item $json = $json->allow_blessed ([$enable])
		485
		486	=item $enabled = $json->get_allow_blessed
		487
		488	If C<$enable> is true (or missing), then the C<encode> method will not
		489	barf when it encounters a blessed reference. Instead, the value of the
		490	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
		491	disabled or no C<TO_JSON> method found) or a representation of the
		492	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
		493	encoded. Has no effect on C<decode>.
		494
		495	If C<$enable> is false (the default), then C<encode> will throw an
		496	exception when it encounters a blessed object.
		497
		498	=item $json = $json->convert_blessed ([$enable])
		499
		500	=item $enabled = $json->get_convert_blessed
		501
		502	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		503	blessed object, will check for the availability of the C<TO_JSON> method
		504	on the object's class. If found, it will be called in scalar context
		505	and the resulting scalar will be encoded instead of the object. If no
		506	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
		507	to do.
		508
		509	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		510	returns other blessed objects, those will be handled in the same
		511	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		512	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		513	methods called by the Perl core (== not by the user of the object) are
		514	usually in upper case letters and to avoid collisions with any C<to_json>
		515	function or method.
		516
		517	This setting does not yet influence C<decode> in any way, but in the
		518	future, global hooks might get installed that influence C<decode> and are
		519	enabled by this setting.
		520
		521	If C<$enable> is false, then the C<allow_blessed> setting will decide what
		522	to do when a blessed object is found.
		523
		524	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		525
		526	When C<$coderef> is specified, it will be called from C<decode> each
		527	time it decodes a JSON object. The only argument is a reference to the
		528	newly-created hash. If the code references returns a single scalar (which
		529	need not be a reference), this value (i.e. a copy of that scalar to avoid
		530	aliasing) is inserted into the deserialised data structure. If it returns
		531	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		532	original deserialised hash will be inserted. This setting can slow down
		533	decoding considerably.
		534
		535	When C<$coderef> is omitted or undefined, any existing callback will
		536	be removed and C<decode> will not change the deserialised hash in any
		537	way.
		538
		539	Example, convert all JSON objects into the integer 5:
		540
		541	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		542	# returns [5]
		543	$js->decode ('[{}]')
		544	# throw an exception because allow_nonref is not enabled
		545	# so a lone 5 is not allowed.
		546	$js->decode ('{"a":1, "b":2}');
		547
		548	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		549
		550	Works remotely similar to C<filter_json_object>, but is only called for
		551	JSON objects having a single key named C<$key>.
		552
		553	This C<$coderef> is called before the one specified via
		554	C<filter_json_object>, if any. It gets passed the single value in the JSON
		555	object. If it returns a single value, it will be inserted into the data
		556	structure. If it returns nothing (not even C<undef> but the empty list),
		557	the callback from C<filter_json_object> will be called next, as if no
		558	single-key callback were specified.
		559
		560	If C<$coderef> is omitted or undefined, the corresponding callback will be
		561	disabled. There can only ever be one callback for a given key.
		562
		563	As this callback gets called less often then the C<filter_json_object>
		564	one, decoding speed will not usually suffer as much. Therefore, single-key
		565	objects make excellent targets to serialise Perl objects into, especially
		566	as single-key JSON objects are as close to the type-tagged value concept
		567	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		568	support this in any way, so you need to make sure your data never looks
		569	like a serialised Perl hash.
		570
		571	Typical names for the single object key are C<__class_whatever__>, or
		572	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		573	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		574	with real hashes.
		575
		576	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		577	into the corresponding C<< $WIDGET{<id>} >> object:
		578
		579	# return whatever is in $WIDGET{5}:
		580	JSON::XS
		581	->new
		582	->filter_json_single_key_object (__widget__ => sub {
		583	$WIDGET{ $_[0] }
		584	})
		585	->decode ('{"__widget__": 5')
		586
		587	# this can be used with a TO_JSON method in some "widget" class
		588	# for serialisation to json:
		589	sub WidgetBase::TO_JSON {
		590	my ($self) = @_;
		591
		592	unless ($self->{id}) {
		593	$self->{id} = ..get..some..id..;
		594	$WIDGET{$self->{id}} = $self;
		595	}
		596
		597	{ __widget__ => $self->{id} }
		598	}
		599
277	=item $json = $json->shrink ([$enable])	600	=item $json = $json->shrink ([$enable])
278		601
		602	=item $enabled = $json->get_shrink
		603
279	Perl usually over-allocates memory a bit when allocating space for	604	Perl usually over-allocates memory a bit when allocating space for
280	strings. This flag optionally resizes strings generated by either	605	strings. This flag optionally resizes strings generated by either
281	C<encode> or C<decode> to their minimum size possible. This can save	606	C<encode> or C<decode> to their minimum size possible. This can save
282	memory when your JSON texts are either very very long or you have many	607	memory when your JSON texts are either very very long or you have many
283	short strings. It will also try to downgrade any strings to octet-form	608	short strings. It will also try to downgrade any strings to octet-form
284	if possible: perl stores strings internally either in an encoding called	609	if possible: perl stores strings internally either in an encoding called
285	UTF-X or in octet-form. The latter cannot store everything but uses less	610	UTF-X or in octet-form. The latter cannot store everything but uses less
286	space in general.	611	space in general (and some buggy Perl or C code might even rely on that
		612	internal representation being used).
287		613
		614	The actual definition of what shrink does might change in future versions,
		615	but it will always try to save space at the expense of time.
		616
288	If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit,	617	If C<$enable> is true (or missing), the string returned by C<encode> will
289	while all strings generated by C<decode> will also be shrunk-to-fit.	618	be shrunk-to-fit, while all strings generated by C<decode> will also be
		619	shrunk-to-fit.
290		620
291	If C<$enable> is false, then the normal perl allocation algorithms are used.	621	If C<$enable> is false, then the normal perl allocation algorithms are used.
292	If you work with your data, then this is likely to be faster.	622	If you work with your data, then this is likely to be faster.
293		623
294	In the future, this setting might control other things, such as converting	624	In the future, this setting might control other things, such as converting
295	strings that look like integers or floats into integers or floats	625	strings that look like integers or floats into integers or floats
296	internally (there is no difference on the Perl level), saving space.	626	internally (there is no difference on the Perl level), saving space.
		627
		628	=item $json = $json->max_depth ([$maximum_nesting_depth])
		629
		630	=item $max_depth = $json->get_max_depth
		631
		632	Sets the maximum nesting level (default C<512>) accepted while encoding
		633	or decoding. If the JSON text or Perl data structure has an equal or
		634	higher nesting level then this limit, then the encoder and decoder will
		635	stop and croak at that point.
		636
		637	Nesting level is defined by number of hash- or arrayrefs that the encoder
		638	needs to traverse to reach a given point or the number of C<{> or C<[>
		639	characters without their matching closing parenthesis crossed to reach a
		640	given character in a string.
		641
		642	Setting the maximum depth to one disallows any nesting, so that ensures
		643	that the object is only a single hash/object or array.
		644
		645	The argument to C<max_depth> will be rounded up to the next highest power
		646	of two. If no argument is given, the highest possible setting will be
		647	used, which is rarely useful.
		648
		649	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		650
		651	=item $json = $json->max_size ([$maximum_string_size])
		652
		653	=item $max_size = $json->get_max_size
		654
		655	Set the maximum length a JSON text may have (in bytes) where decoding is
		656	being attempted. The default is C<0>, meaning no limit. When C<decode>
		657	is called on a string longer then this number of characters it will not
		658	attempt to decode the string but throw an exception. This setting has no
		659	effect on C<encode> (yet).
		660
		661	The argument to C<max_size> will be rounded up to the next B<highest>
		662	power of two (so may be more than requested). If no argument is given, the
		663	limit check will be deactivated (same as when C<0> is specified).
		664
		665	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
297		666
298	=item $json_text = $json->encode ($perl_scalar)	667	=item $json_text = $json->encode ($perl_scalar)
299		668
300	Converts the given Perl data structure (a simple scalar or a reference	669	Converts the given Perl data structure (a simple scalar or a reference
301	to a hash or array) to its JSON representation. Simple scalars will be	670	to a hash or array) to its JSON representation. Simple scalars will be
…		…
311		680
312	JSON numbers and strings become simple Perl scalars. JSON arrays become	681	JSON numbers and strings become simple Perl scalars. JSON arrays become
313	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	682	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
314	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.	683	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
315		684
		685	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		686
		687	This works like the C<decode> method, but instead of raising an exception
		688	when there is trailing garbage after the first JSON object, it will
		689	silently stop parsing there and return the number of characters consumed
		690	so far.
		691
		692	This is useful if your JSON texts are not delimited by an outer protocol
		693	(which is not the brightest thing to do in the first place) and you need
		694	to know where the JSON text ends.
		695
		696	JSON::XS->new->decode_prefix ("[1] the tail")
		697	=> ([], 3)
		698
316	=back	699	=back
		700
		701
		702	=head1 INCREMENTAL PARSING
		703
		704	[This section and the API it details is still EXPERIMENTAL]
		705
		706	In some cases, there is the need for incremental parsing of JSON
		707	texts. While this module always has to keep both JSON text and resulting
		708	Perl data structure in memory at one time, it does allow you to parse a
		709	JSON stream incrementally. It does so by accumulating text until it has
		710	a full JSON object, which it then can decode. This process is similar to
		711	using C<decode_prefix> to see if a full JSON object is available, but is
		712	much more efficient (JSON::XS will only attempt to parse the JSON text
		713	once it is sure it has enough text to get a decisive result, using a very
		714	simple but truly incremental parser).
		715
		716	The following two methods deal with this.
		717
		718	=over 4
		719
		720	=item [void, scalar or list context] = $json->incr_parse ([$string])
		721
		722	This is the central parsing function. It can both append new text and
		723	extract objects from the stream accumulated so far (both of these
		724	functions are optional).
		725
		726	If C<$string> is given, then this string is appended to the already
		727	existing JSON fragment stored in the C<$json> object.
		728
		729	After that, if the function is called in void context, it will simply
		730	return without doing anything further. This can be used to add more text
		731	in as many chunks as you want.
		732
		733	If the method is called in scalar context, then it will try to extract
		734	exactly I<one> JSON object. If that is successful, it will return this
		735	object, otherwise it will return C<undef>. If there is a parse error,
		736	this method will croak just as C<decode> would do (one can then use
		737	C<incr_skip> to skip the errornous part). This is the most common way of
		738	using the method.
		739
		740	And finally, in list context, it will try to extract as many objects
		741	from the stream as it can find and return them, or the empty list
		742	otherwise. For this to work, there must be no separators between the JSON
		743	objects or arrays, instead they must be concatenated back-to-back. If
		744	an error occurs, an exception will be raised as in the scalar context
		745	case. Note that in this case, any previously-parsed JSON texts will be
		746	lost.
		747
		748	=item $lvalue_string = $json->incr_text
		749
		750	This method returns the currently stored JSON fragment as an lvalue, that
		751	is, you can manipulate it. This I<only> works when a preceding call to
		752	C<incr_parse> in I<scalar context> successfully returned an object. Under
		753	all other circumstances you must not call this function (I mean it.
		754	although in simple tests it might actually work, it I<will> fail under
		755	real world conditions). As a special exception, you can also call this
		756	method before having parsed anything.
		757
		758	This function is useful in two cases: a) finding the trailing text after a
		759	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		760	(such as commas).
		761
		762	=item $json->incr_skip
		763
		764	This will reset the state of the incremental parser and will remove the
		765	parsed text from the input buffer. This is useful after C<incr_parse>
		766	died, in which case the input buffer and incremental parser state is left
		767	unchanged, to skip the text parsed so far and to reset the parse state.
		768
		769	=back
		770
		771	=head2 LIMITATIONS
		772
		773	All options that affect decoding are supported, except
		774	C<allow_nonref>. The reason for this is that it cannot be made to
		775	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		776	them back to back and still decode them perfectly. This does not hold true
		777	for JSON numbers, however.
		778
		779	For example, is the string C<1> a single JSON number, or is it simply the
		780	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		781	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		782	takes the conservative route and disallows this case.
		783
		784	=head2 EXAMPLES
		785
		786	Some examples will make all this clearer. First, a simple example that
		787	works similarly to C<decode_prefix>: We want to decode the JSON object at
		788	the start of a string and identify the portion after the JSON object:
		789
		790	my $text = "[1,2,3] hello";
		791
		792	my $json = new JSON::XS;
		793
		794	my $obj = $json->incr_parse ($text)
		795	or die "expected JSON object or array at beginning of string";
		796
		797	my $tail = $json->incr_text;
		798	# $tail now contains " hello"
		799
		800	Easy, isn't it?
		801
		802	Now for a more complicated example: Imagine a hypothetical protocol where
		803	you read some requests from a TCP stream, and each request is a JSON
		804	array, without any separation between them (in fact, it is often useful to
		805	use newlines as "separators", as these get interpreted as whitespace at
		806	the start of the JSON text, which makes it possible to test said protocol
		807	with C<telnet>...).
		808
		809	Here is how you'd do it (it is trivial to write this in an event-based
		810	manner):
		811
		812	my $json = new JSON::XS;
		813
		814	# read some data from the socket
		815	while (sysread $socket, my $buf, 4096) {
		816
		817	# split and decode as many requests as possible
		818	for my $request ($json->incr_parse ($buf)) {
		819	# act on the $request
		820	}
		821	}
		822
		823	Another complicated example: Assume you have a string with JSON objects
		824	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		825	[3]>). To parse them, we have to skip the commas between the JSON texts,
		826	and here is where the lvalue-ness of C<incr_text> comes in useful:
		827
		828	my $text = "[1],[2], [3]";
		829	my $json = new JSON::XS;
		830
		831	# void context, so no parsing done
		832	$json->incr_parse ($text);
		833
		834	# now extract as many objects as possible. note the
		835	# use of scalar context so incr_text can be called.
		836	while (my $obj = $json->incr_parse) {
		837	# do something with $obj
		838
		839	# now skip the optional comma
		840	$json->incr_text =~ s/^ \s* , //x;
		841	}
		842
		843	Now lets go for a very complex example: Assume that you have a gigantic
		844	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		845	but you cannot load it into memory fully (this has actually happened in
		846	the real world :).
		847
		848	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		849	can still help you: You implement a (very simple) array parser and let
		850	JSON decode the array elements, which are all full JSON objects on their
		851	own (this wouldn't work if the array elements could be JSON numbers, for
		852	example):
		853
		854	my $json = new JSON::XS;
		855
		856	# open the monster
		857	open my $fh, "<bigfile.json"
		858	or die "bigfile: $!";
		859
		860	# first parse the initial "["
		861	for (;;) {
		862	sysread $fh, my $buf, 65536
		863	or die "read error: $!";
		864	$json->incr_parse ($buf); # void context, so no parsing
		865
		866	# Exit the loop once we found and removed(!) the initial "[".
		867	# In essence, we are (ab-)using the $json object as a simple scalar
		868	# we append data to.
		869	last if $json->incr_text =~ s/^ \s* \[ //x;
		870	}
		871
		872	# now we have the skipped the initial "[", so continue
		873	# parsing all the elements.
		874	for (;;) {
		875	# in this loop we read data until we got a single JSON object
		876	for (;;) {
		877	if (my $obj = $json->incr_parse) {
		878	# do something with $obj
		879	last;
		880	}
		881
		882	# add more data
		883	sysread $fh, my $buf, 65536
		884	or die "read error: $!";
		885	$json->incr_parse ($buf); # void context, so no parsing
		886	}
		887
		888	# in this loop we read data until we either found and parsed the
		889	# separating "," between elements, or the final "]"
		890	for (;;) {
		891	# first skip whitespace
		892	$json->incr_text =~ s/^\s*//;
		893
		894	# if we find "]", we are done
		895	if ($json->incr_text =~ s/^\]//) {
		896	print "finished.\n";
		897	exit;
		898	}
		899
		900	# if we find ",", we can continue with the next element
		901	if ($json->incr_text =~ s/^,//) {
		902	last;
		903	}
		904
		905	# if we find anything else, we have a parse error!
		906	if (length $json->incr_text) {
		907	die "parse error near ", $json->incr_text;
		908	}
		909
		910	# else add more data
		911	sysread $fh, my $buf, 65536
		912	or die "read error: $!";
		913	$json->incr_parse ($buf); # void context, so no parsing
		914	}
		915
		916	This is a complex example, but most of the complexity comes from the fact
		917	that we are trying to be correct (bear with me if I am wrong, I never ran
		918	the above example :).
		919
		920
317		921
318	=head1 MAPPING	922	=head1 MAPPING
319		923
320	This section describes how JSON::XS maps Perl values to JSON values and	924	This section describes how JSON::XS maps Perl values to JSON values and
321	vice versa. These mappings are designed to "do the right thing" in most	925	vice versa. These mappings are designed to "do the right thing" in most
322	circumstances automatically, preserving round-tripping characteristics	926	circumstances automatically, preserving round-tripping characteristics
323	(what you put in comes out as something equivalent).	927	(what you put in comes out as something equivalent).
324		928
325	For the more enlightened: note that in the following descriptions,	929	For the more enlightened: note that in the following descriptions,
326	lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>	930	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
327	refers to the abstract Perl language itself.	931	refers to the abstract Perl language itself.
328		932
		933
329	=head2 JSON -> PERL	934	=head2 JSON -> PERL
330		935
331	=over 4	936	=over 4
332		937
333	=item object	938	=item object
334		939
335	A JSON object becomes a reference to a hash in Perl. No ordering of object	940	A JSON object becomes a reference to a hash in Perl. No ordering of object
336	keys is preserved (JSON does not preserver object key ordering itself).	941	keys is preserved (JSON does not preserve object key ordering itself).
337		942
338	=item array	943	=item array
339		944
340	A JSON array becomes a reference to an array in Perl.	945	A JSON array becomes a reference to an array in Perl.
341		946
…		…
345	are represented by the same codepoints in the Perl string, so no manual	950	are represented by the same codepoints in the Perl string, so no manual
346	decoding is necessary.	951	decoding is necessary.
347		952
348	=item number	953	=item number
349		954
350	A JSON number becomes either an integer or numeric (floating point)	955	A JSON number becomes either an integer, numeric (floating point) or
351	scalar in perl, depending on its range and any fractional parts. On the	956	string scalar in perl, depending on its range and any fractional parts. On
352	Perl level, there is no difference between those as Perl handles all the	957	the Perl level, there is no difference between those as Perl handles all
353	conversion details, but an integer may take slightly less memory and might	958	the conversion details, but an integer may take slightly less memory and
354	represent more values exactly than (floating point) numbers.	959	might represent more values exactly than floating point numbers.
		960
		961	If the number consists of digits only, JSON::XS will try to represent
		962	it as an integer value. If that fails, it will try to represent it as
		963	a numeric (floating point) value if that is possible without loss of
		964	precision. Otherwise it will preserve the number as a string value (in
		965	which case you lose roundtripping ability, as the JSON number will be
		966	re-encoded toa JSON string).
		967
		968	Numbers containing a fractional or exponential part will always be
		969	represented as numeric (floating point) values, possibly at a loss of
		970	precision (in which case you might lose perfect roundtripping ability, but
		971	the JSON number will still be re-encoded as a JSON number).
355		972
356	=item true, false	973	=item true, false
357		974
358	These JSON atoms become C<0>, C<1>, respectively. Information is lost in	975	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
359	this process. Future versions might represent those values differently,	976	respectively. They are overloaded to act almost exactly like the numbers
360	but they will be guarenteed to act like these integers would normally in	977	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
361	Perl.	978	the C<JSON::XS::is_bool> function.
362		979
363	=item null	980	=item null
364		981
365	A JSON null atom becomes C<undef> in Perl.	982	A JSON null atom becomes C<undef> in Perl.
366		983
367	=back	984	=back
		985
368		986
369	=head2 PERL -> JSON	987	=head2 PERL -> JSON
370		988
371	The mapping from Perl to JSON is slightly more difficult, as Perl is a	989	The mapping from Perl to JSON is slightly more difficult, as Perl is a
372	truly typeless language, so we can only guess which JSON type is meant by	990	truly typeless language, so we can only guess which JSON type is meant by
…		…
375	=over 4	993	=over 4
376		994
377	=item hash references	995	=item hash references
378		996
379	Perl hash references become JSON objects. As there is no inherent ordering	997	Perl hash references become JSON objects. As there is no inherent ordering
380	in hash keys, they will usually be encoded in a pseudo-random order that	998	in hash keys (or JSON objects), they will usually be encoded in a
381	can change between runs of the same program but stays generally the same	999	pseudo-random order that can change between runs of the same program but
382	within a single run of a program. JSON::XS can optionally sort the hash	1000	stays generally the same within a single run of a program. JSON::XS can
383	keys (determined by the I<canonical> flag), so the same datastructure	1001	optionally sort the hash keys (determined by the I<canonical> flag), so
384	will serialise to the same JSON text (given same settings and version of	1002	the same datastructure will serialise to the same JSON text (given same
385	JSON::XS), but this incurs a runtime overhead.	1003	settings and version of JSON::XS), but this incurs a runtime overhead
		1004	and is only rarely useful, e.g. when you want to compare some JSON text
		1005	against another for equality.
386		1006
387	=item array references	1007	=item array references
388		1008
389	Perl array references become JSON arrays.	1009	Perl array references become JSON arrays.
390		1010
		1011	=item other references
		1012
		1013	Other unblessed references are generally not allowed and will cause an
		1014	exception to be thrown, except for references to the integers C<0> and
		1015	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
		1016	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
		1017
		1018	encode_json [\0,JSON::XS::true] # yields [false,true]
		1019
		1020	=item JSON::XS::true, JSON::XS::false
		1021
		1022	These special values become JSON true and JSON false values,
		1023	respectively. You can also use C<\1> and C<\0> directly if you want.
		1024
391	=item blessed objects	1025	=item blessed objects
392		1026
393	Blessed objects are not allowed. JSON::XS currently tries to encode their	1027	Blessed objects are not directly representable in JSON. See the
394	underlying representation (hash- or arrayref), but this behaviour might	1028	C<allow_blessed> and C<convert_blessed> methods on various options on
395	change in future versions.	1029	how to deal with this: basically, you can choose between throwing an
		1030	exception, encoding the reference as if it weren't blessed, or provide
		1031	your own serialiser method.
396		1032
397	=item simple scalars	1033	=item simple scalars
398		1034
399	Simple Perl scalars (any scalar that is not a reference) are the most	1035	Simple Perl scalars (any scalar that is not a reference) are the most
400	difficult objects to encode: JSON::XS will encode undefined scalars as	1036	difficult objects to encode: JSON::XS will encode undefined scalars as
401	JSON null value, scalars that have last been used in a string context	1037	JSON C<null> values, scalars that have last been used in a string context
402	before encoding as JSON strings and anything else as number value:	1038	before encoding as JSON strings, and anything else as number value:
403		1039
404	# dump as number	1040	# dump as number
405	to_json [2] # yields [2]	1041	encode_json [2] # yields [2]
406	to_json [-3.0e17] # yields [-3e+17]	1042	encode_json [-3.0e17] # yields [-3e+17]
407	my $value = 5; to_json [$value] # yields [5]	1043	my $value = 5; encode_json [$value] # yields [5]
408		1044
409	# used as string, so dump as string	1045	# used as string, so dump as string
410	print $value;	1046	print $value;
411	to_json [$value] # yields ["5"]	1047	encode_json [$value] # yields ["5"]
412		1048
413	# undef becomes null	1049	# undef becomes null
414	to_json [undef] # yields [null]	1050	encode_json [undef] # yields [null]
415		1051
416	You can force the type to be a string by stringifying it:	1052	You can force the type to be a JSON string by stringifying it:
417		1053
418	my $x = 3.1; # some variable containing a number	1054	my $x = 3.1; # some variable containing a number
419	"$x"; # stringified	1055	"$x"; # stringified
420	$x .= ""; # another, more awkward way to stringify	1056	$x .= ""; # another, more awkward way to stringify
421	print $x; # perl does it for you, too, quite often	1057	print $x; # perl does it for you, too, quite often
422		1058
423	You can force the type to be a number by numifying it:	1059	You can force the type to be a JSON number by numifying it:
424		1060
425	my $x = "3"; # some variable containing a string	1061	my $x = "3"; # some variable containing a string
426	$x += 0; # numify it, ensuring it will be dumped as a number	1062	$x += 0; # numify it, ensuring it will be dumped as a number
427	$x *= 1; # same thing, the choise is yours.	1063	$x *= 1; # same thing, the choice is yours.
428		1064
429	You can not currently output JSON booleans or force the type in other,	1065	You can not currently force the type in other, less obscure, ways. Tell me
430	less obscure, ways. Tell me if you need this capability.	1066	if you need this capability (but don't forget to explain why it's needed
431		1067	:).
432	=item circular data structures
433
434	Those will be encoded until memory or stackspace runs out.
435		1068
436	=back	1069	=back
437		1070
438	=head1 COMPARISON
439		1071
440	As already mentioned, this module was created because none of the existing	1072	=head1 ENCODING/CODESET FLAG NOTES
441	JSON modules could be made to work correctly. First I will describe the	1073
442	problems (or pleasures) I encountered with various existing JSON modules,	1074	The interested reader might have seen a number of flags that signify
443	followed by some benchmark values. JSON::XS was designed not to suffer	1075	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
444	from any of these problems or limitations.	1076	some confusion on what these do, so here is a short comparison:
		1077
		1078	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1079	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1080	control whether C<encode> escapes character values outside their respective
		1081	codeset range. Neither of these flags conflict with each other, although
		1082	some combinations make less sense than others.
		1083
		1084	Care has been taken to make all flags symmetrical with respect to
		1085	C<encode> and C<decode>, that is, texts encoded with any combination of
		1086	these flag values will be correctly decoded when the same flags are used
		1087	- in general, if you use different flag settings while encoding vs. when
		1088	decoding you likely have a bug somewhere.
		1089
		1090	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1091	simply an abstract set of character-codepoint pairs, while an encoding
		1092	takes those codepoint numbers and I<encodes> them, in our case into
		1093	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1094	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1095	the same time, which can be confusing.
445		1096
446	=over 4	1097	=over 4
447		1098
448	=item JSON 1.07	1099	=item C<utf8> flag disabled
449		1100
450	Slow (but very portable, as it is written in pure Perl).	1101	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1102	and expect Unicode strings, that is, characters with high ordinal Unicode
		1103	values (> 255) will be encoded as such characters, and likewise such
		1104	characters are decoded as-is, no canges to them will be done, except
		1105	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1106	respectively (to Perl, these are the same thing in strings unless you do
		1107	funny/weird/dumb stuff).
451		1108
452	Undocumented/buggy Unicode handling (how JSON handles unicode values is	1109	This is useful when you want to do the encoding yourself (e.g. when you
453	undocumented. One can get far by feeding it unicode strings and doing	1110	want to have UTF-16 encoded JSON texts) or when some other layer does
454	en-/decoding oneself, but unicode escapes are not working properly).	1111	the encoding for you (for example, when printing to a terminal using a
		1112	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1113	to UTF-8 encode your data first and have Perl encode it another time).
455		1114
456	No roundtripping (strings get clobbered if they look like numbers, e.g.	1115	=item C<utf8> flag enabled
457	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
458	decode into the number 2.
459		1116
460	=item JSON::PC 0.01	1117	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1118	characters using the corresponding UTF-8 multi-byte sequence, and will
		1119	expect your input strings to be encoded as UTF-8, that is, no "character"
		1120	of the input string must have any value > 255, as UTF-8 does not allow
		1121	that.
461		1122
462	Very fast.	1123	The C<utf8> flag therefore switches between two modes: disabled means you
		1124	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1125	octet/binary string in Perl.
463		1126
464	Undocumented/buggy Unicode handling.	1127	=item C<latin1> or C<ascii> flags enabled
465		1128
466	No roundtripping.	1129	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1130	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1131	characters as specified by the C<utf8> flag.
467		1132
468	Has problems handling many Perl values (e.g. regex results and other magic	1133	If C<utf8> is disabled, then the result is also correctly encoded in those
469	values will make it croak).	1134	character sets (as both are proper subsets of Unicode, meaning that a
		1135	Unicode string with all character values < 256 is the same thing as a
		1136	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1137	the same thing as an ASCII string in Perl).
470		1138
471	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1139	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
472	which is not a valid JSON text.	1140	regardless of these flags, just some more characters will be escaped using
		1141	C<\uXXXX> then before.
473		1142
474	Unmaintained (maintainer unresponsive for many months, bugs are not	1143	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
475	getting fixed).	1144	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1145	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1146	a subset of Unicode), while ASCII is.
476		1147
477	=item JSON::Syck 0.21	1148	Surprisingly, C<decode> will ignore these flags and so treat all input
		1149	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1150	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1151	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
478		1152
479	Very buggy (often crashes).	1153	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1154	they only govern when the JSON output engine escapes a character or not.
480		1155
481	Very inflexible (no human-readable format supported, format pretty much	1156	The main use for C<latin1> is to relatively efficiently store binary data
482	undocumented. I need at least a format for easy reading by humans and a	1157	as JSON, at the expense of breaking compatibility with most JSON decoders.
483	single-line compact format for use in a protocol, and preferably a way to
484	generate ASCII-only JSON texts).
485		1158
486	Completely broken (and confusingly documented) Unicode handling (unicode	1159	The main use for C<ascii> is to force the output to not contain characters
487	escapes are not working properly, you need to set ImplicitUnicode to	1160	with values > 127, which means you can interpret the resulting string
488	I<different> values on en- and decoding to get symmetric behaviour).	1161	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
489		1162	8-bit-encoding, and still get the same data structure back. This is useful
490	No roundtripping (simple cases work, but this depends on wether the scalar	1163	when your channel for JSON transfer is not 8-bit clean or the encoding
491	value was used in a numeric context or not).	1164	might be mangled in between (e.g. in mail), and works because ASCII is a
492		1165	proper subset of most 8-bit and multibyte encodings in use in the world.
493	Dumping hashes may skip hash values depending on iterator state.
494
495	Unmaintained (maintainer unresponsive for many months, bugs are not
496	getting fixed).
497
498	Does not check input for validity (i.e. will accept non-JSON input and
499	return "something" instead of raising an exception. This is a security
500	issue: imagine two banks transfering money between each other using
501	JSON. One bank might parse a given non-JSON request and deduct money,
502	while the other might reject the transaction with a syntax error. While a
503	good protocol will at least recover, that is extra unnecessary work and
504	the transaction will still not succeed).
505
506	=item JSON::DWIW 0.04
507
508	Very fast. Very natural. Very nice.
509
510	Undocumented unicode handling (but the best of the pack. Unicode escapes
511	still don't get parsed properly).
512
513	Very inflexible.
514
515	No roundtripping.
516
517	Does not generate valid JSON texts (key strings are often unquoted, empty keys
518	result in nothing being output)
519
520	Does not check input for validity.
521		1166
522	=back	1167	=back
		1168
		1169
		1170	=head2 JSON and YAML
		1171
		1172	You often hear that JSON is a subset of YAML. This is, however, a mass
		1173	hysteria(*) and very far from the truth (as of the time of this writing),
		1174	so let me state it clearly: I<in general, there is no way to configure
		1175	JSON::XS to output a data structure as valid YAML> that works in all
		1176	cases.
		1177
		1178	If you really must use JSON::XS to generate YAML, you should use this
		1179	algorithm (subject to change in future versions):
		1180
		1181	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1182	my $yaml = $to_yaml->encode ($ref) . "\n";
		1183
		1184	This will I<usually> generate JSON texts that also parse as valid
		1185	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1186	lengths that JSON doesn't have and also has different and incompatible
		1187	unicode handling, so you should make sure that your hash keys are
		1188	noticeably shorter than the 1024 "stream characters" YAML allows and that
		1189	you do not have characters with codepoint values outside the Unicode BMP
		1190	(basic multilingual page). YAML also does not allow C<\/> sequences in
		1191	strings (which JSON::XS does not I<currently> generate, but other JSON
		1192	generators might).
		1193
		1194	There might be other incompatibilities that I am not aware of (or the YAML
		1195	specification has been changed yet again - it does so quite often). In
		1196	general you should not try to generate YAML with a JSON generator or vice
		1197	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1198	high that you will run into severe interoperability problems when you
		1199	least expect it.
		1200
		1201	=over 4
		1202
		1203	=item (*)
		1204
		1205	I have been pressured multiple times by Brian Ingerson (one of the
		1206	authors of the YAML specification) to remove this paragraph, despite him
		1207	acknowledging that the actual incompatibilities exist. As I was personally
		1208	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1209	educate people about these issues, so others do not run into the same
		1210	problem again and again. After this, Brian called me a (quote)I<complete
		1211	and worthless idiot>(unquote).
		1212
		1213	In my opinion, instead of pressuring and insulting people who actually
		1214	clarify issues with YAML and the wrong statements of some of its
		1215	proponents, I would kindly suggest reading the JSON spec (which is not
		1216	that difficult or long) and finally make YAML compatible to it, and
		1217	educating users about the changes, instead of spreading lies about the
		1218	real compatibility for many I<years> and trying to silence people who
		1219	point out that it isn't true.
		1220
		1221	=back
		1222
523		1223
524	=head2 SPEED	1224	=head2 SPEED
525		1225
526	It seems that JSON::XS is surprisingly fast, as shown in the following	1226	It seems that JSON::XS is surprisingly fast, as shown in the following
527	tables. They have been generated with the help of the C<eg/bench> program	1227	tables. They have been generated with the help of the C<eg/bench> program
528	in the JSON::XS distribution, to make it easy to compare on your own	1228	in the JSON::XS distribution, to make it easy to compare on your own
529	system.	1229	system.
530		1230
531	First comes a comparison between various modules using a very short JSON	1231	First comes a comparison between various modules using
532	string (83 bytes), showing the number of encodes/decodes per second	1232	a very short single-line JSON string (also available at
		1233	L<http://dist.schmorp.de/misc/json/short.json>).
		1234
		1235	{"method": "handleMessage", "params": ["user1", "we were just talking"], \
		1236	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
		1237
		1238	It shows the number of encodes/decodes per second (JSON::XS uses
533	(JSON::XS is the functional interface, while JSON::XS/2 is the OO	1239	the functional interface, while JSON::XS/2 uses the OO interface
534	interface with pretty-printing and hashkey sorting enabled). Higher is	1240	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
535	better:	1241	shrink). Higher is better:
536		1242
537	module | encode | decode |	1243	module | encode | decode |
538	-----------|------------|------------|	1244	-----------|------------|------------|
539	JSON | 14006 | 6820 |	1245	JSON 1.x | 4990.842 | 4088.813 |
540	JSON::DWIW | 200937 | 120386 |	1246	JSON::DWIW | 51653.990 | 71575.154 |
541	JSON::PC | 85065 | 129366 |	1247	JSON::PC | 65948.176 | 74631.744 |
542	JSON::Syck | 59898 | 44232 |	1248	JSON::PP | 8931.652 | 3817.168 |
543	JSON::XS | 1171478 | 342435 |	1249	JSON::Syck | 24877.248 | 27776.848 |
544	JSON::XS/2 | 730760 | 328714 |	1250	JSON::XS | 388361.481 | 227951.304 |
		1251	JSON::XS/2 | 227951.304 | 218453.333 |
		1252	JSON::XS/3 | 338250.323 | 218453.333 |
		1253	Storable | 16500.016 | 135300.129 |
545	-----------+------------+------------+	1254	-----------+------------+------------+
546		1255
547	That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80	1256	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
		1257	about three times faster on decoding, and over forty times faster
548	times faster than JSON, even with pretty-printing and key sorting.	1258	than JSON, even with pretty-printing and key sorting. It also compares
		1259	favourably to Storable for small amounts of data.
549		1260
550	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1261	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
551	search API (http://nanoref.com/yahooapis/mgPdGg):	1262	search API (L<http://dist.schmorp.de/misc/json/long.json>).
552		1263
553	module | encode | decode |	1264	module | encode | decode |
554	-----------|------------|------------|	1265	-----------|------------|------------|
555	JSON | 673 | 38 |	1266	JSON 1.x | 55.260 | 34.971 |
556	JSON::DWIW | 5271 | 770 |	1267	JSON::DWIW | 825.228 | 1082.513 |
557	JSON::PC | 9901 | 2491 |	1268	JSON::PC | 3571.444 | 2394.829 |
558	JSON::Syck | 2360 | 786 |	1269	JSON::PP | 210.987 | 32.574 |
559	JSON::XS | 37398 | 3202 |	1270	JSON::Syck | 552.551 | 787.544 |
560	JSON::XS/2 | 13765 | 3153 |	1271	JSON::XS | 5780.463 | 4854.519 |
		1272	JSON::XS/2 | 3869.998 | 4798.975 |
		1273	JSON::XS/3 | 5862.880 | 4798.975 |
		1274	Storable | 4445.002 | 5235.027 |
561	-----------+------------+------------+	1275	-----------+------------+------------+
562		1276
563	Again, JSON::XS leads by far in the encoding case, while still beating	1277	Again, JSON::XS leads by far (except for Storable which non-surprisingly
564	every other module in the decoding case.	1278	decodes faster).
565		1279
566	On large strings containing lots of unicode characters, some modules	1280	On large strings containing lots of high Unicode characters, some modules
567	(such as JSON::PC) decode faster than JSON::XS, but the result will be	1281	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
568	broken due to missing unicode handling. Others refuse to decode or encode	1282	will be broken due to missing (or wrong) Unicode handling. Others refuse
569	properly, so it was impossible to prepare a fair comparison table for that	1283	to decode or encode properly, so it was impossible to prepare a fair
570	case.	1284	comparison table for that case.
571		1285
572	=head1 RESOURCE LIMITS
573		1286
574	JSON::XS does not impose any limits on the size of JSON texts or Perl	1287	=head1 SECURITY CONSIDERATIONS
575	values they represent - if your machine can handle it, JSON::XS will	1288
576	encode or decode it. Future versions might optionally impose structure	1289	When you are using JSON in a protocol, talking to untrusted potentially
577	depth and memory use resource limits.	1290	hostile creatures requires relatively few measures.
		1291
		1292	First of all, your JSON decoder should be secure, that is, should not have
		1293	any buffer overflows. Obviously, this module should ensure that and I am
		1294	trying hard on making that true, but you never know.
		1295
		1296	Second, you need to avoid resource-starving attacks. That means you should
		1297	limit the size of JSON texts you accept, or make sure then when your
		1298	resources run out, that's just fine (e.g. by using a separate process that
		1299	can crash safely). The size of a JSON text in octets or characters is
		1300	usually a good indication of the size of the resources required to decode
		1301	it into a Perl structure. While JSON::XS can check the size of the JSON
		1302	text, it might be too late when you already have it in memory, so you
		1303	might want to check the size before you accept the string.
		1304
		1305	Third, JSON::XS recurses using the C stack when decoding objects and
		1306	arrays. The C stack is a limited resource: for instance, on my amd64
		1307	machine with 8MB of stack size I can decode around 180k nested arrays but
		1308	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		1309	to free the temporary). If that is exceeded, the program crashes. To be
		1310	conservative, the default nesting limit is set to 512. If your process
		1311	has a smaller stack, you should adjust this setting accordingly with the
		1312	C<max_depth> method.
		1313
		1314	Something else could bomb you, too, that I forgot to think of. In that
		1315	case, you get to keep the pieces. I am always open for hints, though...
		1316
		1317	Also keep in mind that JSON::XS might leak contents of your Perl data
		1318	structures in its error messages, so when you serialise sensitive
		1319	information you might want to make sure that exceptions thrown by JSON::XS
		1320	will not end up in front of untrusted eyes.
		1321
		1322	If you are using JSON::XS to return packets to consumption
		1323	by JavaScript scripts in a browser you should have a look at
		1324	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1325	you are vulnerable to some common attack vectors (which really are browser
		1326	design bugs, but it is still you who will have to deal with it, as major
		1327	browser developers care only for features, not about getting security
		1328	right).
		1329
		1330
		1331	=head1 THREADS
		1332
		1333	This module is I<not> guaranteed to be thread safe and there are no
		1334	plans to change this until Perl gets thread support (as opposed to the
		1335	horribly slow so-called "threads" which are simply slow and bloated
		1336	process simulations - use fork, it's I<much> faster, cheaper, better).
		1337
		1338	(It might actually work, but you have been warned).
		1339
578		1340
579	=head1 BUGS	1341	=head1 BUGS
580		1342
581	While the goal of this module is to be correct, that unfortunately does	1343	While the goal of this module is to be correct, that unfortunately does
582	not mean its bug-free, only that I think its design is bug-free. It is	1344	not mean it's bug-free, only that I think its design is bug-free. It is
583	still very young and not well-tested. If you keep reporting bugs they will	1345	still relatively early in its development. If you keep reporting bugs they
584	be fixed swiftly, though.	1346	will be fixed swiftly, though.
		1347
		1348	Please refrain from using rt.cpan.org or any other bug reporting
		1349	service. I put the contact address into my modules for a reason.
585		1350
586	=cut	1351	=cut
587		1352
		1353	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
		1354	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
		1355
		1356	sub true() { $true }
		1357	sub false() { $false }
		1358
		1359	sub is_bool($) {
		1360	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
		1361	# or UNIVERSAL::isa $_[0], "JSON::Literal"
		1362	}
		1363
		1364	XSLoader::load "JSON::XS", $VERSION;
		1365
		1366	package JSON::XS::Boolean;
		1367
		1368	use overload
		1369	"0+" => sub { ${$_[0]} },
		1370	"++" => sub { $_[0] = ${$_[0]} + 1 },
		1371	"--" => sub { $_[0] = ${$_[0]} - 1 },
		1372	fallback => 1;
		1373
588	1;	1374	1;
		1375
		1376	=head1 SEE ALSO
		1377
		1378	The F<json_xs> command line utility for quick experiments.
589		1379
590	=head1 AUTHOR	1380	=head1 AUTHOR
591		1381
592	Marc Lehmann <schmorp@schmorp.de>	1382	Marc Lehmann <schmorp@schmorp.de>
593	http://home.schmorp.de/	1383	http://home.schmorp.de/

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