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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.19 by root, Sat Mar 24 22:57:12 2007 UTC vs.
Revision 1.95 by root, Tue Mar 25 16:56:09 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 = '0.7';	108	our $VERSION = '2.1';
84	@ISA = qw(Exporter);	109	our @ISA = qw(Exporter);
85		110
86	@EXPORT = qw(to_json from_json);	111	our @EXPORT = qw(encode_json decode_json to_json from_json);
87	require Exporter;
88		112
		113	sub to_json($) {
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 = $json->allow_blessed ([$enable])
		469
		470	=item $enabled = $json->get_allow_blessed
		471
		472	If C<$enable> is true (or missing), then the C<encode> method will not
		473	barf when it encounters a blessed reference. Instead, the value of the
		474	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
		475	disabled or no C<TO_JSON> method found) or a representation of the
		476	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
		477	encoded. Has no effect on C<decode>.
		478
		479	If C<$enable> is false (the default), then C<encode> will throw an
		480	exception when it encounters a blessed object.
		481
		482	=item $json = $json->convert_blessed ([$enable])
		483
		484	=item $enabled = $json->get_convert_blessed
		485
		486	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		487	blessed object, will check for the availability of the C<TO_JSON> method
		488	on the object's class. If found, it will be called in scalar context
		489	and the resulting scalar will be encoded instead of the object. If no
		490	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
		491	to do.
		492
		493	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		494	returns other blessed objects, those will be handled in the same
		495	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		496	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		497	methods called by the Perl core (== not by the user of the object) are
		498	usually in upper case letters and to avoid collisions with any C<to_json>
		499	function or method.
		500
		501	This setting does not yet influence C<decode> in any way, but in the
		502	future, global hooks might get installed that influence C<decode> and are
		503	enabled by this setting.
		504
		505	If C<$enable> is false, then the C<allow_blessed> setting will decide what
		506	to do when a blessed object is found.
		507
		508	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		509
		510	When C<$coderef> is specified, it will be called from C<decode> each
		511	time it decodes a JSON object. The only argument is a reference to the
		512	newly-created hash. If the code references returns a single scalar (which
		513	need not be a reference), this value (i.e. a copy of that scalar to avoid
		514	aliasing) is inserted into the deserialised data structure. If it returns
		515	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		516	original deserialised hash will be inserted. This setting can slow down
		517	decoding considerably.
		518
		519	When C<$coderef> is omitted or undefined, any existing callback will
		520	be removed and C<decode> will not change the deserialised hash in any
		521	way.
		522
		523	Example, convert all JSON objects into the integer 5:
		524
		525	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		526	# returns [5]
		527	$js->decode ('[{}]')
		528	# throw an exception because allow_nonref is not enabled
		529	# so a lone 5 is not allowed.
		530	$js->decode ('{"a":1, "b":2}');
		531
		532	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		533
		534	Works remotely similar to C<filter_json_object>, but is only called for
		535	JSON objects having a single key named C<$key>.
		536
		537	This C<$coderef> is called before the one specified via
		538	C<filter_json_object>, if any. It gets passed the single value in the JSON
		539	object. If it returns a single value, it will be inserted into the data
		540	structure. If it returns nothing (not even C<undef> but the empty list),
		541	the callback from C<filter_json_object> will be called next, as if no
		542	single-key callback were specified.
		543
		544	If C<$coderef> is omitted or undefined, the corresponding callback will be
		545	disabled. There can only ever be one callback for a given key.
		546
		547	As this callback gets called less often then the C<filter_json_object>
		548	one, decoding speed will not usually suffer as much. Therefore, single-key
		549	objects make excellent targets to serialise Perl objects into, especially
		550	as single-key JSON objects are as close to the type-tagged value concept
		551	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		552	support this in any way, so you need to make sure your data never looks
		553	like a serialised Perl hash.
		554
		555	Typical names for the single object key are C<__class_whatever__>, or
		556	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		557	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		558	with real hashes.
		559
		560	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		561	into the corresponding C<< $WIDGET{<id>} >> object:
		562
		563	# return whatever is in $WIDGET{5}:
		564	JSON::XS
		565	->new
		566	->filter_json_single_key_object (__widget__ => sub {
		567	$WIDGET{ $_[0] }
		568	})
		569	->decode ('{"__widget__": 5')
		570
		571	# this can be used with a TO_JSON method in some "widget" class
		572	# for serialisation to json:
		573	sub WidgetBase::TO_JSON {
		574	my ($self) = @_;
		575
		576	unless ($self->{id}) {
		577	$self->{id} = ..get..some..id..;
		578	$WIDGET{$self->{id}} = $self;
		579	}
		580
		581	{ __widget__ => $self->{id} }
		582	}
		583
277	=item $json = $json->shrink ([$enable])	584	=item $json = $json->shrink ([$enable])
278		585
		586	=item $enabled = $json->get_shrink
		587
279	Perl usually over-allocates memory a bit when allocating space for	588	Perl usually over-allocates memory a bit when allocating space for
280	strings. This flag optionally resizes strings generated by either	589	strings. This flag optionally resizes strings generated by either
281	C<encode> or C<decode> to their minimum size possible. This can save	590	C<encode> or C<decode> to their minimum size possible. This can save
282	memory when your JSON texts are either very very long or you have many	591	memory when your JSON texts are either very very long or you have many
283	short strings. It will also try to downgrade any strings to octet-form	592	short strings. It will also try to downgrade any strings to octet-form
284	if possible: perl stores strings internally either in an encoding called	593	if possible: perl stores strings internally either in an encoding called
285	UTF-X or in octet-form. The latter cannot store everything but uses less	594	UTF-X or in octet-form. The latter cannot store everything but uses less
286	space in general.	595	space in general (and some buggy Perl or C code might even rely on that
		596	internal representation being used).
287		597
		598	The actual definition of what shrink does might change in future versions,
		599	but it will always try to save space at the expense of time.
		600
288	If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit,	601	If C<$enable> is true (or missing), the string returned by C<encode> will
289	while all strings generated by C<decode> will also be shrunk-to-fit.	602	be shrunk-to-fit, while all strings generated by C<decode> will also be
		603	shrunk-to-fit.
290		604
291	If C<$enable> is false, then the normal perl allocation algorithms are used.	605	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.	606	If you work with your data, then this is likely to be faster.
293		607
294	In the future, this setting might control other things, such as converting	608	In the future, this setting might control other things, such as converting
295	strings that look like integers or floats into integers or floats	609	strings that look like integers or floats into integers or floats
296	internally (there is no difference on the Perl level), saving space.	610	internally (there is no difference on the Perl level), saving space.
		611
		612	=item $json = $json->max_depth ([$maximum_nesting_depth])
		613
		614	=item $max_depth = $json->get_max_depth
		615
		616	Sets the maximum nesting level (default C<512>) accepted while encoding
		617	or decoding. If the JSON text or Perl data structure has an equal or
		618	higher nesting level then this limit, then the encoder and decoder will
		619	stop and croak at that point.
		620
		621	Nesting level is defined by number of hash- or arrayrefs that the encoder
		622	needs to traverse to reach a given point or the number of C<{> or C<[>
		623	characters without their matching closing parenthesis crossed to reach a
		624	given character in a string.
		625
		626	Setting the maximum depth to one disallows any nesting, so that ensures
		627	that the object is only a single hash/object or array.
		628
		629	The argument to C<max_depth> will be rounded up to the next highest power
		630	of two. If no argument is given, the highest possible setting will be
		631	used, which is rarely useful.
		632
		633	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		634
		635	=item $json = $json->max_size ([$maximum_string_size])
		636
		637	=item $max_size = $json->get_max_size
		638
		639	Set the maximum length a JSON text may have (in bytes) where decoding is
		640	being attempted. The default is C<0>, meaning no limit. When C<decode>
		641	is called on a string longer then this number of characters it will not
		642	attempt to decode the string but throw an exception. This setting has no
		643	effect on C<encode> (yet).
		644
		645	The argument to C<max_size> will be rounded up to the next B<highest>
		646	power of two (so may be more than requested). If no argument is given, the
		647	limit check will be deactivated (same as when C<0> is specified).
		648
		649	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
297		650
298	=item $json_text = $json->encode ($perl_scalar)	651	=item $json_text = $json->encode ($perl_scalar)
299		652
300	Converts the given Perl data structure (a simple scalar or a reference	653	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	654	to a hash or array) to its JSON representation. Simple scalars will be
…		…
311		664
312	JSON numbers and strings become simple Perl scalars. JSON arrays become	665	JSON numbers and strings become simple Perl scalars. JSON arrays become
313	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	666	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>.	667	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
315		668
		669	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		670
		671	This works like the C<decode> method, but instead of raising an exception
		672	when there is trailing garbage after the first JSON object, it will
		673	silently stop parsing there and return the number of characters consumed
		674	so far.
		675
		676	This is useful if your JSON texts are not delimited by an outer protocol
		677	(which is not the brightest thing to do in the first place) and you need
		678	to know where the JSON text ends.
		679
		680	JSON::XS->new->decode_prefix ("[1] the tail")
		681	=> ([], 3)
		682
316	=back	683	=back
		684
		685
		686	=head1 INCREMENTAL PARSING
		687
		688	[This section is still EXPERIMENTAL]
		689
		690	In some cases, there is the need for incremental parsing of JSON
		691	texts. While this module always has to keep both JSON text and resulting
		692	Perl data structure in memory at one time, it does allow you to parse a
		693	JSON stream incrementally. It does so by accumulating text until it has
		694	a full JSON object, which it then can decode. This process is similar to
		695	using C<decode_prefix> to see if a full JSON object is available, but is
		696	much more efficient (JSON::XS will only attempt to parse the JSON text
		697	once it is sure it has enough text to get a decisive result, using a very
		698	simple but truly incremental parser).
		699
		700	The following two methods deal with this.
		701
		702	=over 4
		703
		704	=item [void, scalar or list context] = $json->incr_parse ([$string])
		705
		706	This is the central parsing function. It can both append new text and
		707	extract objects from the stream accumulated so far (both of these
		708	functions are optional).
		709
		710	If C<$string> is given, then this string is appended to the already
		711	existing JSON fragment stored in the C<$json> object.
		712
		713	After that, if the function is called in void context, it will simply
		714	return without doing anything further. This can be used to add more text
		715	in as many chunks as you want.
		716
		717	If the method is called in scalar context, then it will try to extract
		718	exactly I<one> JSON object. If that is successful, it will return this
		719	object, otherwise it will return C<undef>. This is the most common way of
		720	using the method.
		721
		722	And finally, in list context, it will try to extract as many objects
		723	from the stream as it can find and return them, or the empty list
		724	otherwise. For this to work, there must be no separators between the JSON
		725	objects or arrays, instead they must be concatenated back-to-back.
		726
		727	=item $lvalue_string = $json->incr_text
		728
		729	This method returns the currently stored JSON fragment as an lvalue, that
		730	is, you can manipulate it. This I<only> works when a preceding call to
		731	C<incr_parse> in I<scalar context> successfully returned an object. Under
		732	all other circumstances you must not call this function (I mean it.
		733	although in simple tests it might actually work, it I<will> fail under
		734	real world conditions). As a special exception, you can also call this
		735	method before having parsed anything.
		736
		737	This function is useful in two cases: a) finding the trailing text after a
		738	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		739	(such as commas).
		740
		741	=back
		742
		743	=head2 LIMITATIONS
		744
		745	All options that affect decoding are supported, except
		746	C<allow_nonref>. The reason for this is that it cannot be made to
		747	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		748	them back to back and still decode them perfectly. This does not hold true
		749	for JSON numbers, however.
		750
		751	For example, is the string C<1> a single JSON number, or is it simply the
		752	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		753	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		754	takes the conservative route and disallows this case.
		755
		756	=head2 EXAMPLES
		757
		758	Some examples will make all this clearer. First, a simple example that
		759	works similarly to C<decode_prefix>: We want to decode the JSON object at
		760	the start of a string and identify the portion after the JSON object:
		761
		762	my $text = "[1,2,3] hello";
		763
		764	my $json = new JSON::XS;
		765
		766	my $obj = $json->incr_parse ($text)
		767	or die "expected JSON object or array at beginning of string";
		768
		769	my $tail = $json->incr_text;
		770	# $tail now contains " hello"
		771
		772	Easy, isn't it?
		773
		774	Now for a more complicated example: Imagine a hypothetical protocol where
		775	you read some requests from a TCP stream, and each request is a JSON
		776	array, without any separation between them (in fact, it is often useful to
		777	use newlines as "separators", as these get interpreted as whitespace at
		778	the start of the JSON text, which makes it possible to test said protocol
		779	with C<telnet>...).
		780
		781	Here is how you'd do it (it is trivial to write this in an event-based
		782	manner):
		783
		784	my $json = new JSON::XS;
		785
		786	# read some data from the socket
		787	while (sysread $socket, my $buf, 4096) {
		788
		789	# split and decode as many requests as possible
		790	for my $request ($json->incr_parse ($buf)) {
		791	# act on the $request
		792	}
		793	}
		794
		795	Another complicated example: Assume you have a string with JSON objects
		796	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		797	[3]>). To parse them, we have to skip the commas between the JSON texts,
		798	and here is where the lvalue-ness of C<incr_text> comes in useful:
		799
		800	my $text = "[1],[2], [3]";
		801	my $json = new JSON::XS;
		802
		803	# void context, so no parsing done
		804	$json->incr_parse ($text);
		805
		806	# now extract as many objects as possible. note the
		807	# use of scalar context so incr_text can be called.
		808	while (my $obj = $json->incr_parse) {
		809	# do something with $obj
		810
		811	# now skip the optional comma
		812	$json->incr_text =~ s/^ \s* , //x;
		813	}
		814
		815	Now lets go for a very complex example: Assume that you have a gigantic
		816	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		817	but you cannot load it into memory fully (this has actually happened in
		818	the real world :).
		819
		820	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		821	can still help you: You implement a (very simple) array parser and let
		822	JSON decode the array elements, which are all full JSON objects on their
		823	own (this wouldn't work if the array elements could be JSON numbers, for
		824	example):
		825
		826	my $json = new JSON::XS;
		827
		828	# open the monster
		829	open my $fh, "<bigfile.json"
		830	or die "bigfile: $!";
		831
		832	# first parse the initial "["
		833	for (;;) {
		834	sysread $fh, my $buf, 65536
		835	or die "read error: $!";
		836	$json->incr_parse ($buf); # void context, so no parsing
		837
		838	# Exit the loop once we found and removed(!) the initial "[".
		839	# In essence, we are (ab-)using the $json object as a simple scalar
		840	# we append data to.
		841	last if $json->incr_text =~ s/^ \s* \[ //x;
		842	}
		843
		844	# now we have the skipped the initial "[", so continue
		845	# parsing all the elements.
		846	for (;;) {
		847	# in this loop we read data until we got a single JSON object
		848	for (;;) {
		849	if (my $obj = $json->incr_parse) {
		850	# do something with $obj
		851	last;
		852	}
		853
		854	# add more data
		855	sysread $fh, my $buf, 65536
		856	or die "read error: $!";
		857	$json->incr_parse ($buf); # void context, so no parsing
		858	}
		859
		860	# in this loop we read data until we either found and parsed the
		861	# separating "," between elements, or the final "]"
		862	for (;;) {
		863	# first skip whitespace
		864	$json->incr_text =~ s/^\s*//;
		865
		866	# if we find "]", we are done
		867	if ($json->incr_text =~ s/^\]//) {
		868	print "finished.\n";
		869	exit;
		870	}
		871
		872	# if we find ",", we can continue with the next element
		873	if ($json->incr_text =~ s/^,//) {
		874	last;
		875	}
		876
		877	# if we find anything else, we have a parse error!
		878	if (length $json->incr_text) {
		879	die "parse error near ", $json->incr_text;
		880	}
		881
		882	# else 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	This is a complex example, but most of the complexity comes from the fact
		889	that we are trying to be correct (bear with me if I am wrong, I never ran
		890	the above example :).
		891
		892
317		893
318	=head1 MAPPING	894	=head1 MAPPING
319		895
320	This section describes how JSON::XS maps Perl values to JSON values and	896	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	897	vice versa. These mappings are designed to "do the right thing" in most
322	circumstances automatically, preserving round-tripping characteristics	898	circumstances automatically, preserving round-tripping characteristics
323	(what you put in comes out as something equivalent).	899	(what you put in comes out as something equivalent).
324		900
325	For the more enlightened: note that in the following descriptions,	901	For the more enlightened: note that in the following descriptions,
326	lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>	902	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
327	refers to the abstract Perl language itself.	903	refers to the abstract Perl language itself.
328		904
		905
329	=head2 JSON -> PERL	906	=head2 JSON -> PERL
330		907
331	=over 4	908	=over 4
332		909
333	=item object	910	=item object
334		911
335	A JSON object becomes a reference to a hash in Perl. No ordering of object	912	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).	913	keys is preserved (JSON does not preserve object key ordering itself).
337		914
338	=item array	915	=item array
339		916
340	A JSON array becomes a reference to an array in Perl.	917	A JSON array becomes a reference to an array in Perl.
341		918
…		…
345	are represented by the same codepoints in the Perl string, so no manual	922	are represented by the same codepoints in the Perl string, so no manual
346	decoding is necessary.	923	decoding is necessary.
347		924
348	=item number	925	=item number
349		926
350	A JSON number becomes either an integer or numeric (floating point)	927	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	928	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	929	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	930	the conversion details, but an integer may take slightly less memory and
354	represent more values exactly than (floating point) numbers.	931	might represent more values exactly than floating point numbers.
		932
		933	If the number consists of digits only, JSON::XS will try to represent
		934	it as an integer value. If that fails, it will try to represent it as
		935	a numeric (floating point) value if that is possible without loss of
		936	precision. Otherwise it will preserve the number as a string value (in
		937	which case you lose roundtripping ability, as the JSON number will be
		938	re-encoded toa JSON string).
		939
		940	Numbers containing a fractional or exponential part will always be
		941	represented as numeric (floating point) values, possibly at a loss of
		942	precision (in which case you might lose perfect roundtripping ability, but
		943	the JSON number will still be re-encoded as a JSON number).
355		944
356	=item true, false	945	=item true, false
357		946
358	These JSON atoms become C<0>, C<1>, respectively. Information is lost in	947	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
359	this process. Future versions might represent those values differently,	948	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	949	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
361	Perl.	950	the C<JSON::XS::is_bool> function.
362		951
363	=item null	952	=item null
364		953
365	A JSON null atom becomes C<undef> in Perl.	954	A JSON null atom becomes C<undef> in Perl.
366		955
367	=back	956	=back
		957
368		958
369	=head2 PERL -> JSON	959	=head2 PERL -> JSON
370		960
371	The mapping from Perl to JSON is slightly more difficult, as Perl is a	961	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	962	truly typeless language, so we can only guess which JSON type is meant by
…		…
375	=over 4	965	=over 4
376		966
377	=item hash references	967	=item hash references
378		968
379	Perl hash references become JSON objects. As there is no inherent ordering	969	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	970	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	971	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	972	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	973	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	974	the same datastructure will serialise to the same JSON text (given same
385	JSON::XS), but this incurs a runtime overhead.	975	settings and version of JSON::XS), but this incurs a runtime overhead
		976	and is only rarely useful, e.g. when you want to compare some JSON text
		977	against another for equality.
386		978
387	=item array references	979	=item array references
388		980
389	Perl array references become JSON arrays.	981	Perl array references become JSON arrays.
390		982
		983	=item other references
		984
		985	Other unblessed references are generally not allowed and will cause an
		986	exception to be thrown, except for references to the integers C<0> and
		987	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
		988	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
		989
		990	encode_json [\0,JSON::XS::true] # yields [false,true]
		991
		992	=item JSON::XS::true, JSON::XS::false
		993
		994	These special values become JSON true and JSON false values,
		995	respectively. You can also use C<\1> and C<\0> directly if you want.
		996
391	=item blessed objects	997	=item blessed objects
392		998
393	Blessed objects are not allowed. JSON::XS currently tries to encode their	999	Blessed objects are not directly representable in JSON. See the
394	underlying representation (hash- or arrayref), but this behaviour might	1000	C<allow_blessed> and C<convert_blessed> methods on various options on
395	change in future versions.	1001	how to deal with this: basically, you can choose between throwing an
		1002	exception, encoding the reference as if it weren't blessed, or provide
		1003	your own serialiser method.
396		1004
397	=item simple scalars	1005	=item simple scalars
398		1006
399	Simple Perl scalars (any scalar that is not a reference) are the most	1007	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	1008	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	1009	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:	1010	before encoding as JSON strings, and anything else as number value:
403		1011
404	# dump as number	1012	# dump as number
405	to_json [2] # yields [2]	1013	encode_json [2] # yields [2]
406	to_json [-3.0e17] # yields [-3e+17]	1014	encode_json [-3.0e17] # yields [-3e+17]
407	my $value = 5; to_json [$value] # yields [5]	1015	my $value = 5; encode_json [$value] # yields [5]
408		1016
409	# used as string, so dump as string	1017	# used as string, so dump as string
410	print $value;	1018	print $value;
411	to_json [$value] # yields ["5"]	1019	encode_json [$value] # yields ["5"]
412		1020
413	# undef becomes null	1021	# undef becomes null
414	to_json [undef] # yields [null]	1022	encode_json [undef] # yields [null]
415		1023
416	You can force the type to be a string by stringifying it:	1024	You can force the type to be a JSON string by stringifying it:
417		1025
418	my $x = 3.1; # some variable containing a number	1026	my $x = 3.1; # some variable containing a number
419	"$x"; # stringified	1027	"$x"; # stringified
420	$x .= ""; # another, more awkward way to stringify	1028	$x .= ""; # another, more awkward way to stringify
421	print $x; # perl does it for you, too, quite often	1029	print $x; # perl does it for you, too, quite often
422		1030
423	You can force the type to be a number by numifying it:	1031	You can force the type to be a JSON number by numifying it:
424		1032
425	my $x = "3"; # some variable containing a string	1033	my $x = "3"; # some variable containing a string
426	$x += 0; # numify it, ensuring it will be dumped as a number	1034	$x += 0; # numify it, ensuring it will be dumped as a number
427	$x *= 1; # same thing, the choise is yours.	1035	$x *= 1; # same thing, the choice is yours.
428		1036
429	You can not currently output JSON booleans or force the type in other,	1037	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.	1038	if you need this capability (but don't forget to explain why it's needed
431		1039	:).
432	=item circular data structures
433
434	Those will be encoded until memory or stackspace runs out.
435		1040
436	=back	1041	=back
437		1042
438	=head1 COMPARISON
439		1043
440	As already mentioned, this module was created because none of the existing	1044	=head1 ENCODING/CODESET FLAG NOTES
441	JSON modules could be made to work correctly. First I will describe the	1045
442	problems (or pleasures) I encountered with various existing JSON modules,	1046	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	1047	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
444	from any of these problems or limitations.	1048	some confusion on what these do, so here is a short comparison:
		1049
		1050	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1051	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1052	control whether C<encode> escapes character values outside their respective
		1053	codeset range. Neither of these flags conflict with each other, although
		1054	some combinations make less sense than others.
		1055
		1056	Care has been taken to make all flags symmetrical with respect to
		1057	C<encode> and C<decode>, that is, texts encoded with any combination of
		1058	these flag values will be correctly decoded when the same flags are used
		1059	- in general, if you use different flag settings while encoding vs. when
		1060	decoding you likely have a bug somewhere.
		1061
		1062	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1063	simply an abstract set of character-codepoint pairs, while an encoding
		1064	takes those codepoint numbers and I<encodes> them, in our case into
		1065	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1066	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1067	the same time, which can be confusing.
445		1068
446	=over 4	1069	=over 4
447		1070
448	=item JSON 1.07	1071	=item C<utf8> flag disabled
449		1072
450	Slow (but very portable, as it is written in pure Perl).	1073	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1074	and expect Unicode strings, that is, characters with high ordinal Unicode
		1075	values (> 255) will be encoded as such characters, and likewise such
		1076	characters are decoded as-is, no canges to them will be done, except
		1077	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1078	respectively (to Perl, these are the same thing in strings unless you do
		1079	funny/weird/dumb stuff).
451		1080
452	Undocumented/buggy Unicode handling (how JSON handles unicode values is	1081	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	1082	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).	1083	the encoding for you (for example, when printing to a terminal using a
		1084	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1085	to UTF-8 encode your data first and have Perl encode it another time).
455		1086
456	No roundtripping (strings get clobbered if they look like numbers, e.g.	1087	=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		1088
460	=item JSON::PC 0.01	1089	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1090	characters using the corresponding UTF-8 multi-byte sequence, and will
		1091	expect your input strings to be encoded as UTF-8, that is, no "character"
		1092	of the input string must have any value > 255, as UTF-8 does not allow
		1093	that.
461		1094
462	Very fast.	1095	The C<utf8> flag therefore switches between two modes: disabled means you
		1096	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1097	octet/binary string in Perl.
463		1098
464	Undocumented/buggy Unicode handling.	1099	=item C<latin1> or C<ascii> flags enabled
465		1100
466	No roundtripping.	1101	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1102	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1103	characters as specified by the C<utf8> flag.
467		1104
468	Has problems handling many Perl values (e.g. regex results and other magic	1105	If C<utf8> is disabled, then the result is also correctly encoded in those
469	values will make it croak).	1106	character sets (as both are proper subsets of Unicode, meaning that a
		1107	Unicode string with all character values < 256 is the same thing as a
		1108	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1109	the same thing as an ASCII string in Perl).
470		1110
471	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1111	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
472	which is not a valid JSON text.	1112	regardless of these flags, just some more characters will be escaped using
		1113	C<\uXXXX> then before.
473		1114
474	Unmaintained (maintainer unresponsive for many months, bugs are not	1115	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
475	getting fixed).	1116	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1117	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1118	a subset of Unicode), while ASCII is.
476		1119
477	=item JSON::Syck 0.21	1120	Surprisingly, C<decode> will ignore these flags and so treat all input
		1121	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1122	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1123	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
478		1124
479	Very buggy (often crashes).	1125	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1126	they only govern when the JSON output engine escapes a character or not.
480		1127
481	Very inflexible (no human-readable format supported, format pretty much	1128	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	1129	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		1130
486	Completely broken (and confusingly documented) Unicode handling (unicode	1131	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	1132	with values > 127, which means you can interpret the resulting string
488	I<different> values on en- and decoding to get symmetric behaviour).	1133	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
489		1134	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	1135	when your channel for JSON transfer is not 8-bit clean or the encoding
491	value was used in a numeric context or not).	1136	might be mangled in between (e.g. in mail), and works because ASCII is a
492		1137	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		1138
522	=back	1139	=back
		1140
		1141
		1142	=head2 JSON and YAML
		1143
		1144	You often hear that JSON is a subset of YAML. This is, however, a mass
		1145	hysteria(*) and very far from the truth (as of the time of this writing),
		1146	so let me state it clearly: I<in general, there is no way to configure
		1147	JSON::XS to output a data structure as valid YAML> that works in all
		1148	cases.
		1149
		1150	If you really must use JSON::XS to generate YAML, you should use this
		1151	algorithm (subject to change in future versions):
		1152
		1153	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1154	my $yaml = $to_yaml->encode ($ref) . "\n";
		1155
		1156	This will I<usually> generate JSON texts that also parse as valid
		1157	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1158	lengths that JSON doesn't have and also has different and incompatible
		1159	unicode handling, so you should make sure that your hash keys are
		1160	noticeably shorter than the 1024 "stream characters" YAML allows and that
		1161	you do not have characters with codepoint values outside the Unicode BMP
		1162	(basic multilingual page). YAML also does not allow C<\/> sequences in
		1163	strings (which JSON::XS does not I<currently> generate, but other JSON
		1164	generators might).
		1165
		1166	There might be other incompatibilities that I am not aware of (or the YAML
		1167	specification has been changed yet again - it does so quite often). In
		1168	general you should not try to generate YAML with a JSON generator or vice
		1169	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1170	high that you will run into severe interoperability problems when you
		1171	least expect it.
		1172
		1173	=over 4
		1174
		1175	=item (*)
		1176
		1177	I have been pressured multiple times by Brian Ingerson (one of the
		1178	authors of the YAML specification) to remove this paragraph, despite him
		1179	acknowledging that the actual incompatibilities exist. As I was personally
		1180	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1181	educate people about these issues, so others do not run into the same
		1182	problem again and again. After this, Brian called me a (quote)I<complete
		1183	and worthless idiot>(unquote).
		1184
		1185	In my opinion, instead of pressuring and insulting people who actually
		1186	clarify issues with YAML and the wrong statements of some of its
		1187	proponents, I would kindly suggest reading the JSON spec (which is not
		1188	that difficult or long) and finally make YAML compatible to it, and
		1189	educating users about the changes, instead of spreading lies about the
		1190	real compatibility for many I<years> and trying to silence people who
		1191	point out that it isn't true.
		1192
		1193	=back
		1194
523		1195
524	=head2 SPEED	1196	=head2 SPEED
525		1197
526	It seems that JSON::XS is surprisingly fast, as shown in the following	1198	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	1199	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	1200	in the JSON::XS distribution, to make it easy to compare on your own
529	system.	1201	system.
530		1202
531	First comes a comparison between various modules using a very short JSON	1203	First comes a comparison between various modules using
532	string:	1204	a very short single-line JSON string (also available at
		1205	L<http://dist.schmorp.de/misc/json/short.json>).
533		1206
534	{"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null}	1207	{"method": "handleMessage", "params": ["user1", "we were just talking"], \
		1208	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
535		1209
536	It shows the number of encodes/decodes per second (JSON::XS uses the	1210	It shows the number of encodes/decodes per second (JSON::XS uses
537	functional interface, while JSON::XS/2 uses the OO interface with	1211	the functional interface, while JSON::XS/2 uses the OO interface
538	pretty-printing and hashkey sorting enabled). Higher is better:	1212	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
		1213	shrink). Higher is better:
539		1214
540	module \| encode \| decode \|	1215	module \| encode \| decode \|
541	-----------\|------------\|------------\|	1216	-----------\|------------\|------------\|
542	JSON \| 11488.516 \| 7823.035 \|	1217	JSON 1.x \| 4990.842 \| 4088.813 \|
543	JSON::DWIW \| 94708.054 \| 129094.260 \|	1218	JSON::DWIW \| 51653.990 \| 71575.154 \|
544	JSON::PC \| 63884.157 \| 128528.212 \|	1219	JSON::PC \| 65948.176 \| 74631.744 \|
545	JSON::Syck \| 34898.677 \| 42096.911 \|	1220	JSON::PP \| 8931.652 \| 3817.168 \|
546	JSON::XS \| 654027.064 \| 396423.669 \|	1221	JSON::Syck \| 24877.248 \| 27776.848 \|
547	JSON::XS/2 \| 371564.190 \| 371725.613 \|	1222	JSON::XS \| 388361.481 \| 227951.304 \|
		1223	JSON::XS/2 \| 227951.304 \| 218453.333 \|
		1224	JSON::XS/3 \| 338250.323 \| 218453.333 \|
		1225	Storable \| 16500.016 \| 135300.129 \|
548	-----------+------------+------------+	1226	-----------+------------+------------+
549		1227
550	That is, JSON::XS is more than six times faster than JSON::DWIW on	1228	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
551	encoding, more than three times faster on decoding, and about thirty times	1229	about three times faster on decoding, and over forty times faster
552	faster than JSON, even with pretty-printing and key sorting.	1230	than JSON, even with pretty-printing and key sorting. It also compares
		1231	favourably to Storable for small amounts of data.
553		1232
554	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1233	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
555	search API (http://nanoref.com/yahooapis/mgPdGg):	1234	search API (L<http://dist.schmorp.de/misc/json/long.json>).
556		1235
557	module \| encode \| decode \|	1236	module \| encode \| decode \|
558	-----------\|------------\|------------\|	1237	-----------\|------------\|------------\|
559	JSON \| 273.023 \| 44.674 \|	1238	JSON 1.x \| 55.260 \| 34.971 \|
560	JSON::DWIW \| 1089.383 \| 1145.704 \|	1239	JSON::DWIW \| 825.228 \| 1082.513 \|
561	JSON::PC \| 3097.419 \| 2393.921 \|	1240	JSON::PC \| 3571.444 \| 2394.829 \|
562	JSON::Syck \| 514.060 \| 843.053 \|	1241	JSON::PP \| 210.987 \| 32.574 \|
563	JSON::XS \| 6479.668 \| 3636.364 \|	1242	JSON::Syck \| 552.551 \| 787.544 \|
564	JSON::XS/2 \| 3774.221 \| 3599.124 \|	1243	JSON::XS \| 5780.463 \| 4854.519 \|
		1244	JSON::XS/2 \| 3869.998 \| 4798.975 \|
		1245	JSON::XS/3 \| 5862.880 \| 4798.975 \|
		1246	Storable \| 4445.002 \| 5235.027 \|
565	-----------+------------+------------+	1247	-----------+------------+------------+
566		1248
567	Again, JSON::XS leads by far.	1249	Again, JSON::XS leads by far (except for Storable which non-surprisingly
		1250	decodes faster).
568		1251
569	On large strings containing lots of high unicode characters, some modules	1252	On large strings containing lots of high Unicode characters, some modules
570	(such as JSON::PC) seem to decode faster than JSON::XS, but the result	1253	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
571	will be broken due to missing (or wrong) unicode handling. Others refuse	1254	will be broken due to missing (or wrong) Unicode handling. Others refuse
572	to decode or encode properly, so it was impossible to prepare a fair	1255	to decode or encode properly, so it was impossible to prepare a fair
573	comparison table for that case.	1256	comparison table for that case.
574		1257
575	=head1 RESOURCE LIMITS
576		1258
577	JSON::XS does not impose any limits on the size of JSON texts or Perl	1259	=head1 SECURITY CONSIDERATIONS
578	values they represent - if your machine can handle it, JSON::XS will	1260
579	encode or decode it. Future versions might optionally impose structure	1261	When you are using JSON in a protocol, talking to untrusted potentially
580	depth and memory use resource limits.	1262	hostile creatures requires relatively few measures.
		1263
		1264	First of all, your JSON decoder should be secure, that is, should not have
		1265	any buffer overflows. Obviously, this module should ensure that and I am
		1266	trying hard on making that true, but you never know.
		1267
		1268	Second, you need to avoid resource-starving attacks. That means you should
		1269	limit the size of JSON texts you accept, or make sure then when your
		1270	resources run out, that's just fine (e.g. by using a separate process that
		1271	can crash safely). The size of a JSON text in octets or characters is
		1272	usually a good indication of the size of the resources required to decode
		1273	it into a Perl structure. While JSON::XS can check the size of the JSON
		1274	text, it might be too late when you already have it in memory, so you
		1275	might want to check the size before you accept the string.
		1276
		1277	Third, JSON::XS recurses using the C stack when decoding objects and
		1278	arrays. The C stack is a limited resource: for instance, on my amd64
		1279	machine with 8MB of stack size I can decode around 180k nested arrays but
		1280	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		1281	to free the temporary). If that is exceeded, the program crashes. To be
		1282	conservative, the default nesting limit is set to 512. If your process
		1283	has a smaller stack, you should adjust this setting accordingly with the
		1284	C<max_depth> method.
		1285
		1286	Something else could bomb you, too, that I forgot to think of. In that
		1287	case, you get to keep the pieces. I am always open for hints, though...
		1288
		1289	Also keep in mind that JSON::XS might leak contents of your Perl data
		1290	structures in its error messages, so when you serialise sensitive
		1291	information you might want to make sure that exceptions thrown by JSON::XS
		1292	will not end up in front of untrusted eyes.
		1293
		1294	If you are using JSON::XS to return packets to consumption
		1295	by JavaScript scripts in a browser you should have a look at
		1296	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1297	you are vulnerable to some common attack vectors (which really are browser
		1298	design bugs, but it is still you who will have to deal with it, as major
		1299	browser developers care only for features, not about getting security
		1300	right).
		1301
		1302
		1303	=head1 THREADS
		1304
		1305	This module is I<not> guaranteed to be thread safe and there are no
		1306	plans to change this until Perl gets thread support (as opposed to the
		1307	horribly slow so-called "threads" which are simply slow and bloated
		1308	process simulations - use fork, it's I<much> faster, cheaper, better).
		1309
		1310	(It might actually work, but you have been warned).
		1311
581		1312
582	=head1 BUGS	1313	=head1 BUGS
583		1314
584	While the goal of this module is to be correct, that unfortunately does	1315	While the goal of this module is to be correct, that unfortunately does
585	not mean its bug-free, only that I think its design is bug-free. It is	1316	not mean it's bug-free, only that I think its design is bug-free. It is
586	still very young and not well-tested. If you keep reporting bugs they will	1317	still relatively early in its development. If you keep reporting bugs they
587	be fixed swiftly, though.	1318	will be fixed swiftly, though.
		1319
		1320	Please refrain from using rt.cpan.org or any other bug reporting
		1321	service. I put the contact address into my modules for a reason.
588		1322
589	=cut	1323	=cut
590		1324
		1325	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
		1326	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
		1327
		1328	sub true() { $true }
		1329	sub false() { $false }
		1330
		1331	sub is_bool($) {
		1332	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
		1333	# or UNIVERSAL::isa $_[0], "JSON::Literal"
		1334	}
		1335
		1336	XSLoader::load "JSON::XS", $VERSION;
		1337
		1338	package JSON::XS::Boolean;
		1339
		1340	use overload
		1341	"0+" => sub { ${$_[0]} },
		1342	"++" => sub { $_[0] = ${$_[0]} + 1 },
		1343	"--" => sub { $_[0] = ${$_[0]} - 1 },
		1344	fallback => 1;
		1345
591	1;	1346	1;
		1347
		1348	=head1 SEE ALSO
		1349
		1350	The F<json_xs> command line utility for quick experiments.
592		1351
593	=head1 AUTHOR	1352	=head1 AUTHOR
594		1353
595	Marc Lehmann <schmorp@schmorp.de>	1354	Marc Lehmann <schmorp@schmorp.de>
596	http://home.schmorp.de/	1355	http://home.schmorp.de/

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Comparing JSON-XS/XS.pm (file contents): Revision 1.19 by root, Sat Mar 24 22:57:12 2007 UTC vs. Revision 1.95 by root, Tue Mar 25 16:56:09 2008 UTC

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Comparing JSON-XS/XS.pm (file contents):
Revision 1.19 by root, Sat Mar 24 22:57:12 2007 UTC vs.
Revision 1.95 by root, Tue Mar 25 16:56:09 2008 UTC