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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.5 by root, Thu Mar 22 21:36:52 2007 UTC vs.
Revision 1.84 by root, Wed Mar 19 02:52:15 2008 UTC

…		…
		1	=encoding utf-8
		2
1	=head1 NAME	3	=head1 NAME
2		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;
		13
		14	# exported functions, they croak on error
		15	# and expect/generate UTF-8
		16
		17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
		18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
		19
		20	# OO-interface
		21
		22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
		23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
		24	$perl_scalar = $coder->decode ($unicode_json_text);
		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.
8		33
9	=head1 DESCRIPTION	34	=head1 DESCRIPTION
10		35
11	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
12	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
13	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.
14		47
15	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
16	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
17	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
18	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
19	reports for other reasons.	52	reports for other reasons.
20		53
21	See COMPARISON, below, for a comparison to some other JSON modules.	54	See COMPARISON, below, for a comparison to some other JSON modules.
22		55
		56	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
		57	vice versa.
		58
23	=head2 FEATURES	59	=head2 FEATURES
24		60
25	=over 4	61	=over 4
26		62
27	=item * correct handling of unicode issues	63	=item * correct Unicode handling
28		64
29	This module knows how to handle Unicode, and even documents how it does so.	65	This module knows how to handle Unicode, documents how and when it does
		66	so, and even documents what "correct" means.
30		67
31	=item * round-trip integrity	68	=item * round-trip integrity
32		69
33	When you serialise a perl data structure using only datatypes supported	70	When you serialise a perl data structure using only datatypes supported
34	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.
35	(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.
36		75
37	=item * strict checking of JSON correctness	76	=item * strict checking of JSON correctness
38		77
39	There is no guessing, no generating of illegal JSON strings by default,	78	There is no guessing, no generating of illegal JSON texts by default,
40	and only JSON is accepted as input (the latter is a security feature).	79	and only JSON is accepted as input by default (the latter is a security
		80	feature).
41		81
42	=item * fast	82	=item * fast
43		83
44	compared to other JSON modules, this module compares favourably.	84	Compared to other JSON modules and other serialisers such as Storable,
		85	this module usually compares favourably in terms of speed, too.
45		86
46	=item * simple to use	87	=item * simple to use
47		88
48	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
49	interface.	90	oriented interface interface.
50		91
51	=item * reasonably versatile output formats	92	=item * reasonably versatile output formats
52		93
53	You can choose between the most compact format possible, a pure-ascii	94	You can choose between the most compact guaranteed-single-line format
54	format, or a pretty-printed format. Or you can combine those features in	95	possible (nice for simple line-based protocols), a pure-ascii format
55	whatever way you like.	96	(for when your transport is not 8-bit clean, still supports the whole
		97	Unicode range), or a pretty-printed format (for when you want to read that
		98	stuff). Or you can combine those features in whatever way you like.
56		99
57	=back	100	=back
58		101
59	=cut	102	=cut
60		103
61	package JSON::XS;	104	package JSON::XS;
62		105
63	BEGIN {	106	use strict;
		107
64	$VERSION = '0.1';	108	our $VERSION = '2.01';
65	@ISA = qw(Exporter);	109	our @ISA = qw(Exporter);
66		110
67	@EXPORT = qw(to_json from_json);	111	our @EXPORT = qw(encode_json decode_json to_json from_json);
68	require Exporter;
69		112
		113	sub to_json($) {
70	require XSLoader;	114	require Carp;
71	XSLoader::load JSON::XS::, $VERSION;	115	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
72	}	116	}
73		117
		118	sub from_json($) {
		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
74	=head1 FUNCTIONAL INTERFACE	126	=head1 FUNCTIONAL INTERFACE
75		127
76	The following convinience methods are provided by this module. They are	128	The following convenience methods are provided by this module. They are
77	exported by default:	129	exported by default:
78		130
79	=over 4	131	=over 4
80		132
81	=item $json_string = to_json $perl_scalar	133	=item $json_text = encode_json $perl_scalar
82		134
83	Converts the given Perl data structure (a simple scalar or a reference to	135	Converts the given Perl data structure to a UTF-8 encoded, binary string
84	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	136	(that is, the string contains octets only). Croaks on error.
85	octets only). Croaks on error.
86		137
87	This function call is functionally identical to C<< JSON::XS->new->utf8	138	This function call is functionally identical to:
88	(1)->encode ($perl_scalar) >>.
89		139
		140	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
		141
		142	except being faster.
		143
90	=item $perl_scalar = from_json $json_string	144	=item $perl_scalar = decode_json $json_text
91		145
92	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	146	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
93	parse that as an UTF-8 encoded JSON string, returning the resulting simple	147	to parse that as an UTF-8 encoded JSON text, returning the resulting
94	scalar or reference. Croaks on error.	148	reference. Croaks on error.
95		149
96	This function call is functionally identical to C<< JSON::XS->new->utf8	150	This function call is functionally identical to:
97	(1)->decode ($json_string) >>.	151
		152	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
		153
		154	except being faster.
		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.
98		164
99	=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
100		215
101	=head1 OBJECT-ORIENTED INTERFACE	216	=head1 OBJECT-ORIENTED INTERFACE
102		217
103	The object oriented interface lets you configure your own encoding or	218	The object oriented interface lets you configure your own encoding or
104	decoding style, within the limits of supported formats.	219	decoding style, within the limits of supported formats.
111	strings. All boolean flags described below are by default I<disabled>.	226	strings. All boolean flags described below are by default I<disabled>.
112		227
113	The mutators for flags all return the JSON object again and thus calls can	228	The mutators for flags all return the JSON object again and thus calls can
114	be chained:	229	be chained:
115		230
116	my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]})	231	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
117	=> {"a": [1, 2]}	232	=> {"a": [1, 2]}
118		233
119	=item $json = $json->ascii ($enable)	234	=item $json = $json->ascii ([$enable])
120		235
		236	=item $enabled = $json->get_ascii
		237
121	If C<$enable> is true, then the C<encode> method will not generate	238	If C<$enable> is true (or missing), then the C<encode> method will not
122	characters outside the code range C<0..127>. Any unicode characters	239	generate characters outside the code range C<0..127> (which is ASCII). Any
123	outside that range will be escaped using either a single \uXXXX (BMP	240	Unicode characters outside that range will be escaped using either a
124	characters) or a double \uHHHH\uLLLLL escape sequence, as per RFC4627.	241	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
		242	as per RFC4627. The resulting encoded JSON text can be treated as a native
		243	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		244	or any other superset of ASCII.
125		245
126	If C<$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
127	characters unless necessary.	247	characters unless required by the JSON syntax or other flags. This results
		248	in a faster and more compact format.
128		249
		250	The main use for this flag is to produce JSON texts that can be
		251	transmitted over a 7-bit channel, as the encoded JSON texts will not
		252	contain any 8 bit characters.
		253
129	JSON::XS->new->ascii (1)->encode (chr 0x10401)	254	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
130	=> \ud801\udc01	255	=> ["\ud801\udc01"]
131		256
		257	=item $json = $json->latin1 ([$enable])
		258
		259	=item $enabled = $json->get_latin1
		260
		261	If C<$enable> is true (or missing), then the C<encode> method will encode
		262	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		263	outside the code range C<0..255>. The resulting string can be treated as a
		264	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		265	will not be affected in any way by this flag, as C<decode> by default
		266	expects Unicode, which is a strict superset of latin1.
		267
		268	If C<$enable> is false, then the C<encode> method will not escape Unicode
		269	characters unless required by the JSON syntax or other flags.
		270
		271	The main use for this flag is efficiently encoding binary data as JSON
		272	text, as most octets will not be escaped, resulting in a smaller encoded
		273	size. The disadvantage is that the resulting JSON text is encoded
		274	in latin1 (and must correctly be treated as such when storing and
		275	transferring), a rare encoding for JSON. It is therefore most useful when
		276	you want to store data structures known to contain binary data efficiently
		277	in files or databases, not when talking to other JSON encoders/decoders.
		278
		279	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		280	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
		281
132	=item $json = $json->utf8 ($enable)	282	=item $json = $json->utf8 ([$enable])
133		283
		284	=item $enabled = $json->get_utf8
		285
134	If C<$enable> is true, then the C<encode> method will encode the JSON	286	If C<$enable> is true (or missing), then the C<encode> method will encode
135	string into UTF-8, as required by many protocols, while the C<decode>	287	the JSON result into UTF-8, as required by many protocols, while the
136	method expects to be handled an UTF-8-encoded string. Please note that	288	C<decode> method expects to be handled an UTF-8-encoded string. Please
137	UTF-8-encoded strings do not contain any characters outside the range	289	note that UTF-8-encoded strings do not contain any characters outside the
138	C<0..255>, they are thus useful for bytewise/binary I/O.	290	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
		291	versions, enabling this option might enable autodetection of the UTF-16
		292	and UTF-32 encoding families, as described in RFC4627.
139		293
140	If C<$enable> is false, then the C<encode> method will return the JSON	294	If C<$enable> is false, then the C<encode> method will return the JSON
141	string as a (non-encoded) unicode string, while C<decode> expects thus a	295	string as a (non-encoded) Unicode string, while C<decode> expects thus a
142	unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	296	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
143	to be done yourself, e.g. using the Encode module.	297	to be done yourself, e.g. using the Encode module.
144		298
		299	Example, output UTF-16BE-encoded JSON:
		300
		301	use Encode;
		302	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
		303
		304	Example, decode UTF-32LE-encoded JSON:
		305
		306	use Encode;
		307	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
		308
145	=item $json = $json->pretty ($enable)	309	=item $json = $json->pretty ([$enable])
146		310
147	This enables (or disables) all of the C<indent>, C<space_before> and	311	This enables (or disables) all of the C<indent>, C<space_before> and
148	C<space_after> (and in the future possibly more) flags in one call to	312	C<space_after> (and in the future possibly more) flags in one call to
149	generate the most readable (or most compact) form possible.	313	generate the most readable (or most compact) form possible.
		314
		315	Example, pretty-print some simple structure:
150		316
151	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})	317	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
152	=>	318	=>
153	{	319	{
154	"a" : [	320	"a" : [
155	1,	321	1,
156	2	322	2
157	]	323	]
158	}	324	}
159		325
160	=item $json = $json->indent ($enable)	326	=item $json = $json->indent ([$enable])
161		327
		328	=item $enabled = $json->get_indent
		329
162	If C<$enable> is true, then the C<encode> method will use a multiline	330	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
163	format as output, putting every array member or object/hash key-value pair	331	format as output, putting every array member or object/hash key-value pair
164	into its own line, identing them properly.	332	into its own line, indenting them properly.
165		333
166	If C<$enable> is false, no newlines or indenting will be produced, and the	334	If C<$enable> is false, no newlines or indenting will be produced, and the
167	resulting JSON strings is guarenteed not to contain any C<newlines>.	335	resulting JSON text is guaranteed not to contain any C<newlines>.
168		336
169	This setting has no effect when decoding JSON strings.	337	This setting has no effect when decoding JSON texts.
170		338
171	=item $json = $json->space_before ($enable)	339	=item $json = $json->space_before ([$enable])
172		340
		341	=item $enabled = $json->get_space_before
		342
173	If C<$enable> is true, then the C<encode> method will add an extra	343	If C<$enable> is true (or missing), then the C<encode> method will add an extra
174	optional space before the C<:> separating keys from values in JSON objects.	344	optional space before the C<:> separating keys from values in JSON objects.
175		345
176	If C<$enable> is false, then the C<encode> method will not add any extra	346	If C<$enable> is false, then the C<encode> method will not add any extra
177	space at those places.	347	space at those places.
178		348
179	This setting has no effect when decoding JSON strings. You will also most	349	This setting has no effect when decoding JSON texts. You will also
180	likely combine this setting with C<space_after>.	350	most likely combine this setting with C<space_after>.
181		351
		352	Example, space_before enabled, space_after and indent disabled:
		353
		354	{"key" :"value"}
		355
182	=item $json = $json->space_after ($enable)	356	=item $json = $json->space_after ([$enable])
183		357
		358	=item $enabled = $json->get_space_after
		359
184	If C<$enable> is true, then the C<encode> method will add an extra	360	If C<$enable> is true (or missing), then the C<encode> method will add an extra
185	optional space after the C<:> separating keys from values in JSON objects	361	optional space after the C<:> separating keys from values in JSON objects
186	and extra whitespace after the C<,> separating key-value pairs and array	362	and extra whitespace after the C<,> separating key-value pairs and array
187	members.	363	members.
188		364
189	If C<$enable> is false, then the C<encode> method will not add any extra	365	If C<$enable> is false, then the C<encode> method will not add any extra
190	space at those places.	366	space at those places.
191		367
192	This setting has no effect when decoding JSON strings.	368	This setting has no effect when decoding JSON texts.
193		369
		370	Example, space_before and indent disabled, space_after enabled:
		371
		372	{"key": "value"}
		373
		374	=item $json = $json->relaxed ([$enable])
		375
		376	=item $enabled = $json->get_relaxed
		377
		378	If C<$enable> is true (or missing), then C<decode> will accept some
		379	extensions to normal JSON syntax (see below). C<encode> will not be
		380	affected in anyway. I<Be aware that this option makes you accept invalid
		381	JSON texts as if they were valid!>. I suggest only to use this option to
		382	parse application-specific files written by humans (configuration files,
		383	resource files etc.)
		384
		385	If C<$enable> is false (the default), then C<decode> will only accept
		386	valid JSON texts.
		387
		388	Currently accepted extensions are:
		389
		390	=over 4
		391
		392	=item * list items can have an end-comma
		393
		394	JSON I<separates> array elements and key-value pairs with commas. This
		395	can be annoying if you write JSON texts manually and want to be able to
		396	quickly append elements, so this extension accepts comma at the end of
		397	such items not just between them:
		398
		399	[
		400	1,
		401	2, <- this comma not normally allowed
		402	]
		403	{
		404	"k1": "v1",
		405	"k2": "v2", <- this comma not normally allowed
		406	}
		407
		408	=item * shell-style '#'-comments
		409
		410	Whenever JSON allows whitespace, shell-style comments are additionally
		411	allowed. They are terminated by the first carriage-return or line-feed
		412	character, after which more white-space and comments are allowed.
		413
		414	[
		415	1, # this comment not allowed in JSON
		416	# neither this one...
		417	]
		418
		419	=back
		420
194	=item $json = $json->canonical ($enable)	421	=item $json = $json->canonical ([$enable])
195		422
		423	=item $enabled = $json->get_canonical
		424
196	If C<$enable> is true, then the C<encode> method will output JSON objects	425	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
197	by sorting their keys. This is adding a comparatively high overhead.	426	by sorting their keys. This is adding a comparatively high overhead.
198		427
199	If C<$enable> is false, then the C<encode> method will output key-value	428	If C<$enable> is false, then the C<encode> method will output key-value
200	pairs in the order Perl stores them (which will likely change between runs	429	pairs in the order Perl stores them (which will likely change between runs
201	of the same script).	430	of the same script).
202		431
203	This option is useful if you want the same data structure to be encoded as	432	This option is useful if you want the same data structure to be encoded as
204	the same JSON string (given the same overall settings). If it is disabled,	433	the same JSON text (given the same overall settings). If it is disabled,
205	the same hash migh be encoded differently even if contains the same data,	434	the same hash might be encoded differently even if contains the same data,
206	as key-value pairs have no inherent ordering in Perl.	435	as key-value pairs have no inherent ordering in Perl.
207		436
208	This setting has no effect when decoding JSON strings.	437	This setting has no effect when decoding JSON texts.
209		438
210	=item $json = $json->allow_nonref ($enable)	439	=item $json = $json->allow_nonref ([$enable])
211		440
		441	=item $enabled = $json->get_allow_nonref
		442
212	If C<$enable> is true, then the C<encode> method can convert a	443	If C<$enable> is true (or missing), then the C<encode> method can convert a
213	non-reference into its corresponding string, number or null JSON value,	444	non-reference into its corresponding string, number or null JSON value,
214	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	445	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
215	values instead of croaking.	446	values instead of croaking.
216		447
217	If C<$enable> is false, then the C<encode> method will croak if it isn't	448	If C<$enable> is false, then the C<encode> method will croak if it isn't
218	passed an arrayref or hashref, as JSON strings must either be an object	449	passed an arrayref or hashref, as JSON texts must either be an object
219	or array. Likewise, C<decode> will croak if given something that is not a	450	or array. Likewise, C<decode> will croak if given something that is not a
220	JSON object or array.	451	JSON object or array.
221		452
		453	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
		454	resulting in an invalid JSON text:
		455
		456	JSON::XS->new->allow_nonref->encode ("Hello, World!")
		457	=> "Hello, World!"
		458
		459	=item $json = $json->allow_blessed ([$enable])
		460
		461	=item $enabled = $json->get_allow_blessed
		462
		463	If C<$enable> is true (or missing), then the C<encode> method will not
		464	barf when it encounters a blessed reference. Instead, the value of the
		465	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
		466	disabled or no C<TO_JSON> method found) or a representation of the
		467	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
		468	encoded. Has no effect on C<decode>.
		469
		470	If C<$enable> is false (the default), then C<encode> will throw an
		471	exception when it encounters a blessed object.
		472
		473	=item $json = $json->convert_blessed ([$enable])
		474
		475	=item $enabled = $json->get_convert_blessed
		476
		477	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		478	blessed object, will check for the availability of the C<TO_JSON> method
		479	on the object's class. If found, it will be called in scalar context
		480	and the resulting scalar will be encoded instead of the object. If no
		481	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
		482	to do.
		483
		484	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		485	returns other blessed objects, those will be handled in the same
		486	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		487	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		488	methods called by the Perl core (== not by the user of the object) are
		489	usually in upper case letters and to avoid collisions with any C<to_json>
		490	function or method.
		491
		492	This setting does not yet influence C<decode> in any way, but in the
		493	future, global hooks might get installed that influence C<decode> and are
		494	enabled by this setting.
		495
		496	If C<$enable> is false, then the C<allow_blessed> setting will decide what
		497	to do when a blessed object is found.
		498
		499	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		500
		501	When C<$coderef> is specified, it will be called from C<decode> each
		502	time it decodes a JSON object. The only argument is a reference to the
		503	newly-created hash. If the code references returns a single scalar (which
		504	need not be a reference), this value (i.e. a copy of that scalar to avoid
		505	aliasing) is inserted into the deserialised data structure. If it returns
		506	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		507	original deserialised hash will be inserted. This setting can slow down
		508	decoding considerably.
		509
		510	When C<$coderef> is omitted or undefined, any existing callback will
		511	be removed and C<decode> will not change the deserialised hash in any
		512	way.
		513
		514	Example, convert all JSON objects into the integer 5:
		515
		516	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		517	# returns [5]
		518	$js->decode ('[{}]')
		519	# throw an exception because allow_nonref is not enabled
		520	# so a lone 5 is not allowed.
		521	$js->decode ('{"a":1, "b":2}');
		522
		523	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		524
		525	Works remotely similar to C<filter_json_object>, but is only called for
		526	JSON objects having a single key named C<$key>.
		527
		528	This C<$coderef> is called before the one specified via
		529	C<filter_json_object>, if any. It gets passed the single value in the JSON
		530	object. If it returns a single value, it will be inserted into the data
		531	structure. If it returns nothing (not even C<undef> but the empty list),
		532	the callback from C<filter_json_object> will be called next, as if no
		533	single-key callback were specified.
		534
		535	If C<$coderef> is omitted or undefined, the corresponding callback will be
		536	disabled. There can only ever be one callback for a given key.
		537
		538	As this callback gets called less often then the C<filter_json_object>
		539	one, decoding speed will not usually suffer as much. Therefore, single-key
		540	objects make excellent targets to serialise Perl objects into, especially
		541	as single-key JSON objects are as close to the type-tagged value concept
		542	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		543	support this in any way, so you need to make sure your data never looks
		544	like a serialised Perl hash.
		545
		546	Typical names for the single object key are C<__class_whatever__>, or
		547	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		548	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		549	with real hashes.
		550
		551	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		552	into the corresponding C<< $WIDGET{<id>} >> object:
		553
		554	# return whatever is in $WIDGET{5}:
		555	JSON::XS
		556	->new
		557	->filter_json_single_key_object (__widget__ => sub {
		558	$WIDGET{ $_[0] }
		559	})
		560	->decode ('{"__widget__": 5')
		561
		562	# this can be used with a TO_JSON method in some "widget" class
		563	# for serialisation to json:
		564	sub WidgetBase::TO_JSON {
		565	my ($self) = @_;
		566
		567	unless ($self->{id}) {
		568	$self->{id} = ..get..some..id..;
		569	$WIDGET{$self->{id}} = $self;
		570	}
		571
		572	{ __widget__ => $self->{id} }
		573	}
		574
		575	=item $json = $json->shrink ([$enable])
		576
		577	=item $enabled = $json->get_shrink
		578
		579	Perl usually over-allocates memory a bit when allocating space for
		580	strings. This flag optionally resizes strings generated by either
		581	C<encode> or C<decode> to their minimum size possible. This can save
		582	memory when your JSON texts are either very very long or you have many
		583	short strings. It will also try to downgrade any strings to octet-form
		584	if possible: perl stores strings internally either in an encoding called
		585	UTF-X or in octet-form. The latter cannot store everything but uses less
		586	space in general (and some buggy Perl or C code might even rely on that
		587	internal representation being used).
		588
		589	The actual definition of what shrink does might change in future versions,
		590	but it will always try to save space at the expense of time.
		591
		592	If C<$enable> is true (or missing), the string returned by C<encode> will
		593	be shrunk-to-fit, while all strings generated by C<decode> will also be
		594	shrunk-to-fit.
		595
		596	If C<$enable> is false, then the normal perl allocation algorithms are used.
		597	If you work with your data, then this is likely to be faster.
		598
		599	In the future, this setting might control other things, such as converting
		600	strings that look like integers or floats into integers or floats
		601	internally (there is no difference on the Perl level), saving space.
		602
		603	=item $json = $json->max_depth ([$maximum_nesting_depth])
		604
		605	=item $max_depth = $json->get_max_depth
		606
		607	Sets the maximum nesting level (default C<512>) accepted while encoding
		608	or decoding. If the JSON text or Perl data structure has an equal or
		609	higher nesting level then this limit, then the encoder and decoder will
		610	stop and croak at that point.
		611
		612	Nesting level is defined by number of hash- or arrayrefs that the encoder
		613	needs to traverse to reach a given point or the number of C<{> or C<[>
		614	characters without their matching closing parenthesis crossed to reach a
		615	given character in a string.
		616
		617	Setting the maximum depth to one disallows any nesting, so that ensures
		618	that the object is only a single hash/object or array.
		619
		620	The argument to C<max_depth> will be rounded up to the next highest power
		621	of two. If no argument is given, the highest possible setting will be
		622	used, which is rarely useful.
		623
		624	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		625
		626	=item $json = $json->max_size ([$maximum_string_size])
		627
		628	=item $max_size = $json->get_max_size
		629
		630	Set the maximum length a JSON text may have (in bytes) where decoding is
		631	being attempted. The default is C<0>, meaning no limit. When C<decode>
		632	is called on a string longer then this number of characters it will not
		633	attempt to decode the string but throw an exception. This setting has no
		634	effect on C<encode> (yet).
		635
		636	The argument to C<max_size> will be rounded up to the next B<highest>
		637	power of two (so may be more than requested). If no argument is given, the
		638	limit check will be deactivated (same as when C<0> is specified).
		639
		640	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		641
222	=item $json_string = $json->encode ($perl_scalar)	642	=item $json_text = $json->encode ($perl_scalar)
223		643
224	Converts the given Perl data structure (a simple scalar or a reference	644	Converts the given Perl data structure (a simple scalar or a reference
225	to a hash or array) to its JSON representation. Simple scalars will be	645	to a hash or array) to its JSON representation. Simple scalars will be
226	converted into JSON string or number sequences, while references to arrays	646	converted into JSON string or number sequences, while references to arrays
227	become JSON arrays and references to hashes become JSON objects. Undefined	647	become JSON arrays and references to hashes become JSON objects. Undefined
228	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>	648	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
229	nor C<false> values will be generated.	649	nor C<false> values will be generated.
230		650
231	=item $perl_scalar = $json->decode ($json_string)	651	=item $perl_scalar = $json->decode ($json_text)
232		652
233	The opposite of C<encode>: expects a JSON string and tries to parse it,	653	The opposite of C<encode>: expects a JSON text and tries to parse it,
234	returning the resulting simple scalar or reference. Croaks on error.	654	returning the resulting simple scalar or reference. Croaks on error.
235		655
236	JSON numbers and strings become simple Perl scalars. JSON arrays become	656	JSON numbers and strings become simple Perl scalars. JSON arrays become
237	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	657	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
238	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.	658	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
239		659
		660	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		661
		662	This works like the C<decode> method, but instead of raising an exception
		663	when there is trailing garbage after the first JSON object, it will
		664	silently stop parsing there and return the number of characters consumed
		665	so far.
		666
		667	This is useful if your JSON texts are not delimited by an outer protocol
		668	(which is not the brightest thing to do in the first place) and you need
		669	to know where the JSON text ends.
		670
		671	JSON::XS->new->decode_prefix ("[1] the tail")
		672	=> ([], 3)
		673
240	=back	674	=back
		675
		676
		677	=head1 MAPPING
		678
		679	This section describes how JSON::XS maps Perl values to JSON values and
		680	vice versa. These mappings are designed to "do the right thing" in most
		681	circumstances automatically, preserving round-tripping characteristics
		682	(what you put in comes out as something equivalent).
		683
		684	For the more enlightened: note that in the following descriptions,
		685	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
		686	refers to the abstract Perl language itself.
		687
		688
		689	=head2 JSON -> PERL
		690
		691	=over 4
		692
		693	=item object
		694
		695	A JSON object becomes a reference to a hash in Perl. No ordering of object
		696	keys is preserved (JSON does not preserve object key ordering itself).
		697
		698	=item array
		699
		700	A JSON array becomes a reference to an array in Perl.
		701
		702	=item string
		703
		704	A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON
		705	are represented by the same codepoints in the Perl string, so no manual
		706	decoding is necessary.
		707
		708	=item number
		709
		710	A JSON number becomes either an integer, numeric (floating point) or
		711	string scalar in perl, depending on its range and any fractional parts. On
		712	the Perl level, there is no difference between those as Perl handles all
		713	the conversion details, but an integer may take slightly less memory and
		714	might represent more values exactly than floating point numbers.
		715
		716	If the number consists of digits only, JSON::XS will try to represent
		717	it as an integer value. If that fails, it will try to represent it as
		718	a numeric (floating point) value if that is possible without loss of
		719	precision. Otherwise it will preserve the number as a string value (in
		720	which case you lose roundtripping ability, as the JSON number will be
		721	re-encoded toa JSON string).
		722
		723	Numbers containing a fractional or exponential part will always be
		724	represented as numeric (floating point) values, possibly at a loss of
		725	precision (in which case you might lose perfect roundtripping ability, but
		726	the JSON number will still be re-encoded as a JSON number).
		727
		728	=item true, false
		729
		730	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
		731	respectively. They are overloaded to act almost exactly like the numbers
		732	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
		733	the C<JSON::XS::is_bool> function.
		734
		735	=item null
		736
		737	A JSON null atom becomes C<undef> in Perl.
		738
		739	=back
		740
		741
		742	=head2 PERL -> JSON
		743
		744	The mapping from Perl to JSON is slightly more difficult, as Perl is a
		745	truly typeless language, so we can only guess which JSON type is meant by
		746	a Perl value.
		747
		748	=over 4
		749
		750	=item hash references
		751
		752	Perl hash references become JSON objects. As there is no inherent ordering
		753	in hash keys (or JSON objects), they will usually be encoded in a
		754	pseudo-random order that can change between runs of the same program but
		755	stays generally the same within a single run of a program. JSON::XS can
		756	optionally sort the hash keys (determined by the I<canonical> flag), so
		757	the same datastructure will serialise to the same JSON text (given same
		758	settings and version of JSON::XS), but this incurs a runtime overhead
		759	and is only rarely useful, e.g. when you want to compare some JSON text
		760	against another for equality.
		761
		762	=item array references
		763
		764	Perl array references become JSON arrays.
		765
		766	=item other references
		767
		768	Other unblessed references are generally not allowed and will cause an
		769	exception to be thrown, except for references to the integers C<0> and
		770	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
		771	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
		772
		773	encode_json [\0,JSON::XS::true] # yields [false,true]
		774
		775	=item JSON::XS::true, JSON::XS::false
		776
		777	These special values become JSON true and JSON false values,
		778	respectively. You can also use C<\1> and C<\0> directly if you want.
		779
		780	=item blessed objects
		781
		782	Blessed objects are not directly representable in JSON. See the
		783	C<allow_blessed> and C<convert_blessed> methods on various options on
		784	how to deal with this: basically, you can choose between throwing an
		785	exception, encoding the reference as if it weren't blessed, or provide
		786	your own serialiser method.
		787
		788	=item simple scalars
		789
		790	Simple Perl scalars (any scalar that is not a reference) are the most
		791	difficult objects to encode: JSON::XS will encode undefined scalars as
		792	JSON C<null> values, scalars that have last been used in a string context
		793	before encoding as JSON strings, and anything else as number value:
		794
		795	# dump as number
		796	encode_json [2] # yields [2]
		797	encode_json [-3.0e17] # yields [-3e+17]
		798	my $value = 5; encode_json [$value] # yields [5]
		799
		800	# used as string, so dump as string
		801	print $value;
		802	encode_json [$value] # yields ["5"]
		803
		804	# undef becomes null
		805	encode_json [undef] # yields [null]
		806
		807	You can force the type to be a JSON string by stringifying it:
		808
		809	my $x = 3.1; # some variable containing a number
		810	"$x"; # stringified
		811	$x .= ""; # another, more awkward way to stringify
		812	print $x; # perl does it for you, too, quite often
		813
		814	You can force the type to be a JSON number by numifying it:
		815
		816	my $x = "3"; # some variable containing a string
		817	$x += 0; # numify it, ensuring it will be dumped as a number
		818	$x *= 1; # same thing, the choice is yours.
		819
		820	You can not currently force the type in other, less obscure, ways. Tell me
		821	if you need this capability (but don't forget to explain why its needed
		822	:).
		823
		824	=back
		825
		826
		827	=head1 ENCODING/CODESET FLAG NOTES
		828
		829	The interested reader might have seen a number of flags that signify
		830	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		831	some confusion on what these do, so here is a short comparison:
		832
		833	C<utf8> controls wether the JSON text created by C<encode> (and expected
		834	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		835	control wether C<encode> escapes character values outside their respective
		836	codeset range. Neither of these flags conflict with each other, although
		837	some combinations make less sense than others.
		838
		839	Care has been taken to make all flags symmetrical with respect to
		840	C<encode> and C<decode>, that is, texts encoded with any combination of
		841	these flag values will be correctly decoded when the same flags are used
		842	- in general, if you use different flag settings while encoding vs. when
		843	decoding you likely have a bug somewhere.
		844
		845	Below comes a verbose discussion of these flags. Note that a "codeset" is
		846	simply an abstract set of character-codepoint pairs, while an encoding
		847	takes those codepoint numbers and I<encodes> them, in our case into
		848	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		849	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		850	the same time, which can be confusing.
		851
		852	=over 4
		853
		854	=item C<utf8> flag disabled
		855
		856	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		857	and expect Unicode strings, that is, characters with high ordinal Unicode
		858	values (> 255) will be encoded as such characters, and likewise such
		859	characters are decoded as-is, no canges to them will be done, except
		860	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		861	respectively (to Perl, these are the same thing in strings unless you do
		862	funny/weird/dumb stuff).
		863
		864	This is useful when you want to do the encoding yourself (e.g. when you
		865	want to have UTF-16 encoded JSON texts) or when some other layer does
		866	the encoding for you (for example, when printing to a terminal using a
		867	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		868	to UTF-8 encode your data first and have Perl encode it another time).
		869
		870	=item C<utf8> flag enabled
		871
		872	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		873	characters using the corresponding UTF-8 multi-byte sequence, and will
		874	expect your input strings to be encoded as UTF-8, that is, no "character"
		875	of the input string must have any value > 255, as UTF-8 does not allow
		876	that.
		877
		878	The C<utf8> flag therefore switches between two modes: disabled means you
		879	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		880	octet/binary string in Perl.
		881
		882	=item C<latin1> or C<ascii> flags enabled
		883
		884	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		885	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		886	characters as specified by the C<utf8> flag.
		887
		888	If C<utf8> is disabled, then the result is also correctly encoded in those
		889	character sets (as both are proper subsets of Unicode, meaning that a
		890	Unicode string with all character values < 256 is the same thing as a
		891	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		892	the same thing as an ASCII string in Perl).
		893
		894	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		895	regardless of these flags, just some more characters will be escaped using
		896	C<\uXXXX> then before.
		897
		898	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		899	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		900	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		901	a subset of Unicode), while ASCII is.
		902
		903	Surprisingly, C<decode> will ignore these flags and so treat all input
		904	values as governed by the C<utf8> flag. If it is disabled, this allows you
		905	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		906	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		907
		908	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		909	they only govern when the JSON output engine escapes a character or not.
		910
		911	The main use for C<latin1> is to relatively efficiently store binary data
		912	as JSON, at the expense of breaking compatibility with most JSON decoders.
		913
		914	The main use for C<ascii> is to force the output to not contain characters
		915	with values > 127, which means you can interpret the resulting string
		916	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		917	8-bit-encoding, and still get the same data structure back. This is useful
		918	when your channel for JSON transfer is not 8-bit clean or the encoding
		919	might be mangled in between (e.g. in mail), and works because ASCII is a
		920	proper subset of most 8-bit and multibyte encodings in use in the world.
		921
		922	=back
		923
241		924
242	=head1 COMPARISON	925	=head1 COMPARISON
243		926
244	As already mentioned, this module was created because none of the existing	927	As already mentioned, this module was created because none of the existing
245	JSON modules could be made to work correctly. First I will describe the	928	JSON modules could be made to work correctly. First I will describe the
…		…
247	followed by some benchmark values. JSON::XS was designed not to suffer	930	followed by some benchmark values. JSON::XS was designed not to suffer
248	from any of these problems or limitations.	931	from any of these problems or limitations.
249		932
250	=over 4	933	=over 4
251		934
		935	=item JSON 2.xx
		936
		937	A marvellous piece of engineering, this module either uses JSON::XS
		938	directly when available (so will be 100% compatible with it, including
		939	speed), or it uses JSON::PP, which is basically JSON::XS translated to
		940	Pure Perl, which should be 100% compatible with JSON::XS, just a bit
		941	slower.
		942
		943	You cannot really lose by using this module.
		944
252	=item JSON 1.07	945	=item JSON 1.07
253		946
254	Slow (but very portable, as it is written in pure Perl).	947	Slow (but very portable, as it is written in pure Perl).
255		948
256	Undocumented/buggy Unicode handling (how JSON handles unicode values is	949	Undocumented/buggy Unicode handling (how JSON handles Unicode values is
257	undocumented. One can get far by feeding it unicode strings and doing	950	undocumented. One can get far by feeding it Unicode strings and doing
258	en-/decoding oneself, but unicode escapes are not working properly).	951	en-/decoding oneself, but Unicode escapes are not working properly).
259		952
260	No roundtripping (strings get clobbered if they look like numbers, e.g.	953	No round-tripping (strings get clobbered if they look like numbers, e.g.
261	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	954	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
262	decode into the number 2.	955	decode into the number 2.
263		956
264	=item JSON::PC 0.01	957	=item JSON::PC 0.01
265		958
266	Very fast.	959	Very fast.
267		960
268	Undocumented/buggy Unicode handling.	961	Undocumented/buggy Unicode handling.
269		962
270	No roundtripping.	963	No round-tripping.
271		964
272	Has problems handling many Perl values (e.g. regex results and other magic	965	Has problems handling many Perl values (e.g. regex results and other magic
273	values will make it croak).	966	values will make it croak).
274		967
275	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	968	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
276	which is not a valid JSON string.	969	which is not a valid JSON text.
277		970
278	Unmaintained (maintainer unresponsive for many months, bugs are not	971	Unmaintained (maintainer unresponsive for many months, bugs are not
279	getting fixed).	972	getting fixed).
280		973
281	=item JSON::Syck 0.21	974	=item JSON::Syck 0.21
…		…
283	Very buggy (often crashes).	976	Very buggy (often crashes).
284		977
285	Very inflexible (no human-readable format supported, format pretty much	978	Very inflexible (no human-readable format supported, format pretty much
286	undocumented. I need at least a format for easy reading by humans and a	979	undocumented. I need at least a format for easy reading by humans and a
287	single-line compact format for use in a protocol, and preferably a way to	980	single-line compact format for use in a protocol, and preferably a way to
288	generate ASCII-only JSON strings).	981	generate ASCII-only JSON texts).
289		982
290	Completely broken (and confusingly documented) Unicode handling (unicode	983	Completely broken (and confusingly documented) Unicode handling (Unicode
291	escapes are not working properly, you need to set ImplicitUnicode to	984	escapes are not working properly, you need to set ImplicitUnicode to
292	I<different> values on en- and decoding to get symmetric behaviour).	985	I<different> values on en- and decoding to get symmetric behaviour).
293		986
294	No roundtripping (simple cases work, but this depends on wether the scalar	987	No round-tripping (simple cases work, but this depends on whether the scalar
295	value was used in a numeric context or not).	988	value was used in a numeric context or not).
296		989
297	Dumping hashes may skip hash values depending on iterator state.	990	Dumping hashes may skip hash values depending on iterator state.
298		991
299	Unmaintained (maintainer unresponsive for many months, bugs are not	992	Unmaintained (maintainer unresponsive for many months, bugs are not
300	getting fixed).	993	getting fixed).
301		994
302	Does not check input for validity (i.e. will accept non-JSON input and	995	Does not check input for validity (i.e. will accept non-JSON input and
303	return "something" instead of raising an exception. This is a security	996	return "something" instead of raising an exception. This is a security
304	issue: imagine two banks transfering money between each other using	997	issue: imagine two banks transferring money between each other using
305	JSON. One bank might parse a given non-JSON request and deduct money,	998	JSON. One bank might parse a given non-JSON request and deduct money,
306	while the other might reject the transaction with a syntax error. While a	999	while the other might reject the transaction with a syntax error. While a
307	good protocol will at least recover, that is extra unnecessary work and	1000	good protocol will at least recover, that is extra unnecessary work and
308	the transaction will still not succeed).	1001	the transaction will still not succeed).
309		1002
310	=item JSON::DWIW 0.04	1003	=item JSON::DWIW 0.04
311		1004
312	Very fast. Very natural. Very nice.	1005	Very fast. Very natural. Very nice.
313		1006
314	Undocumented unicode handling (but the best of the pack. Unicode escapes	1007	Undocumented Unicode handling (but the best of the pack. Unicode escapes
315	still don't get parsed properly).	1008	still don't get parsed properly).
316		1009
317	Very inflexible.	1010	Very inflexible.
318		1011
319	No roundtripping.	1012	No round-tripping.
320		1013
321	Does not generate valid JSON (key strings are often unquoted, empty keys	1014	Does not generate valid JSON texts (key strings are often unquoted, empty keys
322	result in nothing being output)	1015	result in nothing being output)
323		1016
324	Does not check input for validity.	1017	Does not check input for validity.
325		1018
326	=back	1019	=back
		1020
		1021
		1022	=head2 JSON and YAML
		1023
		1024	You often hear that JSON is a subset of YAML. This is, however, a mass
		1025	hysteria(*) and very far from the truth. In general, there is no way to
		1026	configure JSON::XS to output a data structure as valid YAML that works for
		1027	all cases.
		1028
		1029	If you really must use JSON::XS to generate YAML, you should use this
		1030	algorithm (subject to change in future versions):
		1031
		1032	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1033	my $yaml = $to_yaml->encode ($ref) . "\n";
		1034
		1035	This will I<usually> generate JSON texts that also parse as valid
		1036	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1037	lengths that JSON doesn't have and also has different and incompatible
		1038	unicode handling, so you should make sure that your hash keys are
		1039	noticeably shorter than the 1024 "stream characters" YAML allows and that
		1040	you do not have codepoints with values outside the Unicode BMP (basic
		1041	multilingual page). YAML also does not allow C<\/> sequences in strings
		1042	(which JSON::XS does not I<currently> generate).
		1043
		1044	There might be other incompatibilities that I am not aware of (or the YAML
		1045	specification has been changed yet again - it does so quite often). In
		1046	general you should not try to generate YAML with a JSON generator or vice
		1047	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1048	high that you will run into severe interoperability problems when you
		1049	least expect it.
		1050
		1051	=over 4
		1052
		1053	=item (*)
		1054
		1055	This is spread actively by the YAML team, however. For many years now they
		1056	claim YAML were a superset of JSON, even when proven otherwise.
		1057
		1058	Even the author of this manpage was at some point accused of providing
		1059	"incorrect" information, despite the evidence presented (claims ranged
		1060	from "your documentation contains inaccurate and negative statements about
		1061	YAML" (the only negative comment is this footnote, and it didn't exist
		1062	back then; the question on which claims were inaccurate was never answered
		1063	etc.) to "the YAML spec is not up-to-date" (the real and supposedly
		1064	JSON-compatible spec is apparently not currently publicly available)
		1065	to actual requests to replace this section by incorrect information,
		1066	suppressing information about the real problem).
		1067
		1068	So whenever you are told that YAML was a superset of JSON, first check
		1069	wether it is really true (it might be when you check it, but it certainly
		1070	was not true when this was written). I would much prefer if the YAML team
		1071	would spent their time on actually making JSON compatibility a truth
		1072	(JSON, after all, has a very small and simple specification) instead of
		1073	trying to lobby/force people into reporting untruths.
		1074
		1075	=back
		1076
327		1077
328	=head2 SPEED	1078	=head2 SPEED
329		1079
330	It seems that JSON::XS is surprisingly fast, as shown in the following	1080	It seems that JSON::XS is surprisingly fast, as shown in the following
331	tables. They have been generated with the help of the C<eg/bench> program	1081	tables. They have been generated with the help of the C<eg/bench> program
332	in the JSON::XS distribution, to make it easy to compare on your own	1082	in the JSON::XS distribution, to make it easy to compare on your own
333	system.	1083	system.
334		1084
335	First is a comparison between various modules using a very simple JSON	1085	First comes a comparison between various modules using a very short
		1086	single-line JSON string:
		1087
		1088	{"method": "handleMessage", "params": ["user1", "we were just talking"], \
		1089	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
		1090
336	string, showing the number of encodes/decodes per second (JSON::XS is	1091	It shows the number of encodes/decodes per second (JSON::XS uses
337	the functional interface, while JSON::XS/2 is the OO interface with	1092	the functional interface, while JSON::XS/2 uses the OO interface
338	pretty-printing and hashkey sorting enabled).	1093	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
		1094	shrink). Higher is better:
339		1095
340	module \| encode \| decode \|	1096	module \| encode \| decode \|
341	-----------\|------------\|------------\|	1097	-----------\|------------\|------------\|
342	JSON \| 14006 \| 6820 \|	1098	JSON 1.x \| 4990.842 \| 4088.813 \|
343	JSON::DWIW \| 200937 \| 120386 \|	1099	JSON::DWIW \| 51653.990 \| 71575.154 \|
344	JSON::PC \| 85065 \| 129366 \|	1100	JSON::PC \| 65948.176 \| 74631.744 \|
345	JSON::Syck \| 59898 \| 44232 \|	1101	JSON::PP \| 8931.652 \| 3817.168 \|
346	JSON::XS \| 1171478 \| 342435 \|	1102	JSON::Syck \| 24877.248 \| 27776.848 \|
347	JSON::XS/2 \| 730760 \| 328714 \|	1103	JSON::XS \| 388361.481 \| 227951.304 \|
		1104	JSON::XS/2 \| 227951.304 \| 218453.333 \|
		1105	JSON::XS/3 \| 338250.323 \| 218453.333 \|
		1106	Storable \| 16500.016 \| 135300.129 \|
348	-----------+------------+------------+	1107	-----------+------------+------------+
349		1108
350	That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80	1109	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
		1110	about three times faster on decoding, and over forty times faster
351	times faster than JSON, even with pretty-printing and key sorting.	1111	than JSON, even with pretty-printing and key sorting. It also compares
		1112	favourably to Storable for small amounts of data.
352		1113
353	Using a longer test string (roughly 8KB, generated from Yahoo! Locals	1114	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
354	search API (http://nanoref.com/yahooapis/mgPdGg):	1115	search API (http://nanoref.com/yahooapis/mgPdGg):
355		1116
356	module \| encode \| decode \|	1117	module \| encode \| decode \|
357	-----------\|------------\|------------\|	1118	-----------\|------------\|------------\|
358	JSON \| 673 \| 38 \|	1119	JSON 1.x \| 55.260 \| 34.971 \|
359	JSON::DWIW \| 5271 \| 770 \|	1120	JSON::DWIW \| 825.228 \| 1082.513 \|
360	JSON::PC \| 9901 \| 2491 \|	1121	JSON::PC \| 3571.444 \| 2394.829 \|
361	JSON::Syck \| 2360 \| 786 \|	1122	JSON::PP \| 210.987 \| 32.574 \|
362	JSON::XS \| 37398 \| 3202 \|	1123	JSON::Syck \| 552.551 \| 787.544 \|
363	JSON::XS/2 \| 13765 \| 3153 \|	1124	JSON::XS \| 5780.463 \| 4854.519 \|
		1125	JSON::XS/2 \| 3869.998 \| 4798.975 \|
		1126	JSON::XS/3 \| 5862.880 \| 4798.975 \|
		1127	Storable \| 4445.002 \| 5235.027 \|
364	-----------+------------+------------+	1128	-----------+------------+------------+
365		1129
366	Again, JSON::XS leads by far in the encoding case, while still beating	1130	Again, JSON::XS leads by far (except for Storable which non-surprisingly
367	every other module in the decoding case.	1131	decodes faster).
368		1132
369	Last example is an almost 8MB large hash with many large binary values	1133	On large strings containing lots of high Unicode characters, some modules
370	(PNG files), resulting in a lot of escaping:	1134	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
		1135	will be broken due to missing (or wrong) Unicode handling. Others refuse
		1136	to decode or encode properly, so it was impossible to prepare a fair
		1137	comparison table for that case.
		1138
		1139
		1140	=head1 SECURITY CONSIDERATIONS
		1141
		1142	When you are using JSON in a protocol, talking to untrusted potentially
		1143	hostile creatures requires relatively few measures.
		1144
		1145	First of all, your JSON decoder should be secure, that is, should not have
		1146	any buffer overflows. Obviously, this module should ensure that and I am
		1147	trying hard on making that true, but you never know.
		1148
		1149	Second, you need to avoid resource-starving attacks. That means you should
		1150	limit the size of JSON texts you accept, or make sure then when your
		1151	resources run out, that's just fine (e.g. by using a separate process that
		1152	can crash safely). The size of a JSON text in octets or characters is
		1153	usually a good indication of the size of the resources required to decode
		1154	it into a Perl structure. While JSON::XS can check the size of the JSON
		1155	text, it might be too late when you already have it in memory, so you
		1156	might want to check the size before you accept the string.
		1157
		1158	Third, JSON::XS recurses using the C stack when decoding objects and
		1159	arrays. The C stack is a limited resource: for instance, on my amd64
		1160	machine with 8MB of stack size I can decode around 180k nested arrays but
		1161	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		1162	to free the temporary). If that is exceeded, the program crashes. To be
		1163	conservative, the default nesting limit is set to 512. If your process
		1164	has a smaller stack, you should adjust this setting accordingly with the
		1165	C<max_depth> method.
		1166
		1167	And last but least, something else could bomb you that I forgot to think
		1168	of. In that case, you get to keep the pieces. I am always open for hints,
		1169	though...
		1170
		1171	If you are using JSON::XS to return packets to consumption
		1172	by JavaScript scripts in a browser you should have a look at
		1173	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1174	you are vulnerable to some common attack vectors (which really are browser
		1175	design bugs, but it is still you who will have to deal with it, as major
		1176	browser developers care only for features, not about getting security
		1177	right).
		1178
		1179
		1180	=head1 THREADS
		1181
		1182	This module is I<not> guaranteed to be thread safe and there are no
		1183	plans to change this until Perl gets thread support (as opposed to the
		1184	horribly slow so-called "threads" which are simply slow and bloated
		1185	process simulations - use fork, its I<much> faster, cheaper, better).
		1186
		1187	(It might actually work, but you have been warned).
		1188
371		1189
372	=head1 BUGS	1190	=head1 BUGS
373		1191
374	While the goal of this module is to be correct, that unfortunately does	1192	While the goal of this module is to be correct, that unfortunately does
375	not mean its bug-free, only that I think its design is bug-free. It is	1193	not mean its bug-free, only that I think its design is bug-free. It is
376	still very young and not well-tested. If you keep reporting bugs they will	1194	still relatively early in its development. If you keep reporting bugs they
377	be fixed swiftly, though.	1195	will be fixed swiftly, though.
		1196
		1197	Please refrain from using rt.cpan.org or any other bug reporting
		1198	service. I put the contact address into my modules for a reason.
378		1199
379	=cut	1200	=cut
		1201
		1202	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
		1203	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
		1204
		1205	sub true() { $true }
		1206	sub false() { $false }
		1207
		1208	sub is_bool($) {
		1209	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
		1210	# or UNIVERSAL::isa $_[0], "JSON::Literal"
		1211	}
		1212
		1213	XSLoader::load "JSON::XS", $VERSION;
		1214
		1215	package JSON::XS::Boolean;
		1216
		1217	use overload
		1218	"0+" => sub { ${$_[0]} },
		1219	"++" => sub { $_[0] = ${$_[0]} + 1 },
		1220	"--" => sub { $_[0] = ${$_[0]} - 1 },
		1221	fallback => 1;
380		1222
381	1;	1223	1;
382		1224
383	=head1 AUTHOR	1225	=head1 AUTHOR
384		1226

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Comparing JSON-XS/XS.pm (file contents): Revision 1.5 by root, Thu Mar 22 21:36:52 2007 UTC vs. Revision 1.84 by root, Wed Mar 19 02:52:15 2008 UTC

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Revision 1.5 by root, Thu Mar 22 21:36:52 2007 UTC vs.
Revision 1.84 by root, Wed Mar 19 02:52:15 2008 UTC