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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.32 by root, Thu Apr 12 07:25:29 2007 UTC vs.
Revision 1.93 by root, Sat Mar 22 22:21:33 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
		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)
4		9
5	=head1 SYNOPSIS	10	=head1 SYNOPSIS
6		11
7	use JSON::XS;	12	use JSON::XS;
8		13
9	# exported functions, they croak on error	14	# exported functions, they croak on error
10	# and expect/generate UTF-8	15	# and expect/generate UTF-8
11		16
12	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
13	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
14
15	# objToJson and jsonToObj aliases to to_json and from_json
16	# are exported for compatibility to the JSON module,
17	# but should not be used in new code.
18		19
19	# OO-interface	20	# OO-interface
20		21
21	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
22	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
23	$perl_scalar = $coder->decode ($unicode_json_text);	24	$perl_scalar = $coder->decode ($unicode_json_text);
24		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
25	=head1 DESCRIPTION	34	=head1 DESCRIPTION
26		35
27	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
28	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
29	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.
30		47
31	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
32	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
33	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
34	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
41		58
42	=head2 FEATURES	59	=head2 FEATURES
43		60
44	=over 4	61	=over 4
45		62
46	=item * correct unicode handling	63	=item * correct Unicode handling
47		64
48	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
49	it does so.	66	so, and even documents what "correct" means.
50		67
51	=item * round-trip integrity	68	=item * round-trip integrity
52		69
53	When you serialise a perl data structure using only datatypes supported	70	When you serialise a perl data structure using only datatypes supported
54	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.
55	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks	72	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
56	like a number).	73	like a number). There minor I<are> exceptions to this, read the MAPPING
		74	section below to learn about those.
57		75
58	=item * strict checking of JSON correctness	76	=item * strict checking of JSON correctness
59		77
60	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,
61	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
62	feature).	80	feature).
63		81
64	=item * fast	82	=item * fast
65		83
66	Compared to other JSON modules, this module compares favourably in terms	84	Compared to other JSON modules and other serialisers such as Storable,
67	of speed, too.	85	this module usually compares favourably in terms of speed, too.
68		86
69	=item * simple to use	87	=item * simple to use
70		88
71	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
72	interface.	90	oriented interface interface.
73		91
74	=item * reasonably versatile output formats	92	=item * reasonably versatile output formats
75		93
76	You can choose between the most compact guarenteed single-line format	94	You can choose between the most compact guaranteed-single-line format
77	possible (nice for simple line-based protocols), a pure-ascii format	95	possible (nice for simple line-based protocols), a pure-ascii format
78	(for when your transport is not 8-bit clean, still supports the whole	96	(for when your transport is not 8-bit clean, still supports the whole
79	unicode range), or a pretty-printed format (for when you want to read that	97	Unicode range), or a pretty-printed format (for when you want to read that
80	stuff). Or you can combine those features in whatever way you like.	98	stuff). Or you can combine those features in whatever way you like.
81		99
82	=back	100	=back
83		101
84	=cut	102	=cut
85		103
86	package JSON::XS;	104	package JSON::XS;
87		105
88	use strict;	106	use strict;
89		107
90	BEGIN {
91	our $VERSION = '1.12';	108	our $VERSION = '2.1';
92	our @ISA = qw(Exporter);	109	our @ISA = qw(Exporter);
93		110
94	our @EXPORT = qw(to_json from_json objToJson jsonToObj);	111	our @EXPORT = qw(encode_json decode_json to_json from_json);
95	require Exporter;
96		112
		113	sub to_json($) {
97	require XSLoader;	114	require Carp;
98	XSLoader::load JSON::XS::, $VERSION;	115	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
99	}	116	}
100		117
		118	sub from_json($) {
		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
101	=head1 FUNCTIONAL INTERFACE	126	=head1 FUNCTIONAL INTERFACE
102		127
103	The following convinience methods are provided by this module. They are	128	The following convenience methods are provided by this module. They are
104	exported by default:	129	exported by default:
105		130
106	=over 4	131	=over 4
107		132
108	=item $json_text = to_json $perl_scalar	133	=item $json_text = encode_json $perl_scalar
109		134
110	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
111	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.
112	octets only). Croaks on error.
113		137
114	This function call is functionally identical to:	138	This function call is functionally identical to:
115		139
116	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	140	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
117		141
118	except being faster.	142	except being faster.
119		143
120	=item $perl_scalar = from_json $json_text	144	=item $perl_scalar = decode_json $json_text
121		145
122	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
123	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
124	scalar or reference. Croaks on error.	148	reference. Croaks on error.
125		149
126	This function call is functionally identical to:	150	This function call is functionally identical to:
127		151
128	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	152	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
129		153
130	except being faster.	154	except being faster.
131		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
132	=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 :)
133		214
134		215
135	=head1 OBJECT-ORIENTED INTERFACE	216	=head1 OBJECT-ORIENTED INTERFACE
136		217
137	The object oriented interface lets you configure your own encoding or	218	The object oriented interface lets you configure your own encoding or
…		…
150	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]})
151	=> {"a": [1, 2]}	232	=> {"a": [1, 2]}
152		233
153	=item $json = $json->ascii ([$enable])	234	=item $json = $json->ascii ([$enable])
154		235
		236	=item $enabled = $json->get_ascii
		237
155	If C<$enable> is true (or missing), then the C<encode> method will not	238	If C<$enable> is true (or missing), then the C<encode> method will not
156	generate characters outside the code range C<0..127> (which is ASCII). Any	239	generate characters outside the code range C<0..127> (which is ASCII). Any
157	unicode characters outside that range will be escaped using either a	240	Unicode characters outside that range will be escaped using either a
158	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,	241	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
159	as per RFC4627. The resulting encoded JSON text can be treated as a native	242	as per RFC4627. The resulting encoded JSON text can be treated as a native
160	unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,	243	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
161	or any other superset of ASCII.	244	or any other superset of ASCII.
162		245
163	If C<$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
164	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
165	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.
166		256
167	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	257	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
168	=> ["\ud801\udc01"]	258	=> ["\ud801\udc01"]
169		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
170	=item $json = $json->utf8 ([$enable])	288	=item $json = $json->utf8 ([$enable])
		289
		290	=item $enabled = $json->get_utf8
171		291
172	If C<$enable> is true (or missing), then the C<encode> method will encode	292	If C<$enable> is true (or missing), then the C<encode> method will encode
173	the JSON result into UTF-8, as required by many protocols, while the	293	the JSON result into UTF-8, as required by many protocols, while the
174	C<decode> method expects to be handled an UTF-8-encoded string. Please	294	C<decode> method expects to be handled an UTF-8-encoded string. Please
175	note that UTF-8-encoded strings do not contain any characters outside the	295	note that UTF-8-encoded strings do not contain any characters outside the
176	range C<0..255>, they are thus useful for bytewise/binary I/O. In future	296	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
177	versions, enabling this option might enable autodetection of the UTF-16	297	versions, enabling this option might enable autodetection of the UTF-16
178	and UTF-32 encoding families, as described in RFC4627.	298	and UTF-32 encoding families, as described in RFC4627.
179		299
180	If C<$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
181	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
182	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
183	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.
184		307
185	Example, output UTF-16BE-encoded JSON:	308	Example, output UTF-16BE-encoded JSON:
186		309
187	use Encode;	310	use Encode;
188	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	311	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
209	]	332	]
210	}	333	}
211		334
212	=item $json = $json->indent ([$enable])	335	=item $json = $json->indent ([$enable])
213		336
		337	=item $enabled = $json->get_indent
		338
214	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	339	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
215	format as output, putting every array member or object/hash key-value pair	340	format as output, putting every array member or object/hash key-value pair
216	into its own line, identing them properly.	341	into its own line, indenting them properly.
217		342
218	If C<$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
219	resulting JSON text is guarenteed not to contain any C<newlines>.	344	resulting JSON text is guaranteed not to contain any C<newlines>.
220		345
221	This setting has no effect when decoding JSON texts.	346	This setting has no effect when decoding JSON texts.
222		347
223	=item $json = $json->space_before ([$enable])	348	=item $json = $json->space_before ([$enable])
		349
		350	=item $enabled = $json->get_space_before
224		351
225	If C<$enable> is true (or missing), then the C<encode> method will add an extra	352	If C<$enable> is true (or missing), then the C<encode> method will add an extra
226	optional space before the C<:> separating keys from values in JSON objects.	353	optional space before the C<:> separating keys from values in JSON objects.
227		354
228	If C<$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
…		…
234	Example, space_before enabled, space_after and indent disabled:	361	Example, space_before enabled, space_after and indent disabled:
235		362
236	{"key" :"value"}	363	{"key" :"value"}
237		364
238	=item $json = $json->space_after ([$enable])	365	=item $json = $json->space_after ([$enable])
		366
		367	=item $enabled = $json->get_space_after
239		368
240	If C<$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
241	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
242	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
243	members.	372	members.
…		…
249		378
250	Example, space_before and indent disabled, space_after enabled:	379	Example, space_before and indent disabled, space_after enabled:
251		380
252	{"key": "value"}	381	{"key": "value"}
253		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
254	=item $json = $json->canonical ([$enable])	430	=item $json = $json->canonical ([$enable])
		431
		432	=item $enabled = $json->get_canonical
255		433
256	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	434	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
257	by sorting their keys. This is adding a comparatively high overhead.	435	by sorting their keys. This is adding a comparatively high overhead.
258		436
259	If C<$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
260	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
261	of the same script).	439	of the same script).
262		440
263	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
264	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,
265	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,
266	as key-value pairs have no inherent ordering in Perl.	444	as key-value pairs have no inherent ordering in Perl.
267		445
268	This setting has no effect when decoding JSON texts.	446	This setting has no effect when decoding JSON texts.
269		447
270	=item $json = $json->allow_nonref ([$enable])	448	=item $json = $json->allow_nonref ([$enable])
		449
		450	=item $enabled = $json->get_allow_nonref
271		451
272	If C<$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
273	non-reference into its corresponding string, number or null JSON value,	453	non-reference into its corresponding string, number or null JSON value,
274	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
275	values instead of croaking.	455	values instead of croaking.
…		…
283	resulting in an invalid JSON text:	463	resulting in an invalid JSON text:
284		464
285	JSON::XS->new->allow_nonref->encode ("Hello, World!")	465	JSON::XS->new->allow_nonref->encode ("Hello, World!")
286	=> "Hello, World!"	466	=> "Hello, World!"
287		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
288	=item $json = $json->shrink ([$enable])	584	=item $json = $json->shrink ([$enable])
		585
		586	=item $enabled = $json->get_shrink
289		587
290	Perl usually over-allocates memory a bit when allocating space for	588	Perl usually over-allocates memory a bit when allocating space for
291	strings. This flag optionally resizes strings generated by either	589	strings. This flag optionally resizes strings generated by either
292	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
293	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
…		…
311	strings that look like integers or floats into integers or floats	609	strings that look like integers or floats into integers or floats
312	internally (there is no difference on the Perl level), saving space.	610	internally (there is no difference on the Perl level), saving space.
313		611
314	=item $json = $json->max_depth ([$maximum_nesting_depth])	612	=item $json = $json->max_depth ([$maximum_nesting_depth])
315		613
		614	=item $max_depth = $json->get_max_depth
		615
316	Sets the maximum nesting level (default C<512>) accepted while encoding	616	Sets the maximum nesting level (default C<512>) accepted while encoding
317	or decoding. If the JSON text or Perl data structure has an equal or	617	or decoding. If the JSON text or Perl data structure has an equal or
318	higher nesting level then this limit, then the encoder and decoder will	618	higher nesting level then this limit, then the encoder and decoder will
319	stop and croak at that point.	619	stop and croak at that point.
320		620
…		…
324	given character in a string.	624	given character in a string.
325		625
326	Setting the maximum depth to one disallows any nesting, so that ensures	626	Setting the maximum depth to one disallows any nesting, so that ensures
327	that the object is only a single hash/object or array.	627	that the object is only a single hash/object or array.
328		628
329	The argument to C<max_depth> will be rounded up to the next nearest power	629	The argument to C<max_depth> will be rounded up to the next highest power
330	of two.	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).
331		648
332	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	649	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
333		650
334	=item $json_text = $json->encode ($perl_scalar)	651	=item $json_text = $json->encode ($perl_scalar)
335		652
…		…
347		664
348	JSON numbers and strings become simple Perl scalars. JSON arrays become	665	JSON numbers and strings become simple Perl scalars. JSON arrays become
349	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	666	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
350	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>.
351		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
352	=back	683	=back
353		684
354		685
355	=head1 MAPPING	686	=head1 MAPPING
356		687
…		…
358	vice versa. These mappings are designed to "do the right thing" in most	689	vice versa. These mappings are designed to "do the right thing" in most
359	circumstances automatically, preserving round-tripping characteristics	690	circumstances automatically, preserving round-tripping characteristics
360	(what you put in comes out as something equivalent).	691	(what you put in comes out as something equivalent).
361		692
362	For the more enlightened: note that in the following descriptions,	693	For the more enlightened: note that in the following descriptions,
363	lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>	694	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
364	refers to the abstract Perl language itself.	695	refers to the abstract Perl language itself.
365		696
		697
366	=head2 JSON -> PERL	698	=head2 JSON -> PERL
367		699
368	=over 4	700	=over 4
369		701
370	=item object	702	=item object
371		703
372	A JSON object becomes a reference to a hash in Perl. No ordering of object	704	A JSON object becomes a reference to a hash in Perl. No ordering of object
373	keys is preserved (JSON does not preserver object key ordering itself).	705	keys is preserved (JSON does not preserve object key ordering itself).
374		706
375	=item array	707	=item array
376		708
377	A JSON array becomes a reference to an array in Perl.	709	A JSON array becomes a reference to an array in Perl.
378		710
…		…
382	are represented by the same codepoints in the Perl string, so no manual	714	are represented by the same codepoints in the Perl string, so no manual
383	decoding is necessary.	715	decoding is necessary.
384		716
385	=item number	717	=item number
386		718
387	A JSON number becomes either an integer or numeric (floating point)	719	A JSON number becomes either an integer, numeric (floating point) or
388	scalar in perl, depending on its range and any fractional parts. On the	720	string scalar in perl, depending on its range and any fractional parts. On
389	Perl level, there is no difference between those as Perl handles all the	721	the Perl level, there is no difference between those as Perl handles all
390	conversion details, but an integer may take slightly less memory and might	722	the conversion details, but an integer may take slightly less memory and
391	represent more values exactly than (floating point) numbers.	723	might represent more values exactly than floating point numbers.
		724
		725	If the number consists of digits only, JSON::XS will try to represent
		726	it as an integer value. If that fails, it will try to represent it as
		727	a numeric (floating point) value if that is possible without loss of
		728	precision. Otherwise it will preserve the number as a string value (in
		729	which case you lose roundtripping ability, as the JSON number will be
		730	re-encoded toa JSON string).
		731
		732	Numbers containing a fractional or exponential part will always be
		733	represented as numeric (floating point) values, possibly at a loss of
		734	precision (in which case you might lose perfect roundtripping ability, but
		735	the JSON number will still be re-encoded as a JSON number).
392		736
393	=item true, false	737	=item true, false
394		738
395	These JSON atoms become C<0>, C<1>, respectively. Information is lost in	739	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
396	this process. Future versions might represent those values differently,	740	respectively. They are overloaded to act almost exactly like the numbers
397	but they will be guarenteed to act like these integers would normally in	741	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
398	Perl.	742	the C<JSON::XS::is_bool> function.
399		743
400	=item null	744	=item null
401		745
402	A JSON null atom becomes C<undef> in Perl.	746	A JSON null atom becomes C<undef> in Perl.
403		747
404	=back	748	=back
		749
405		750
406	=head2 PERL -> JSON	751	=head2 PERL -> JSON
407		752
408	The mapping from Perl to JSON is slightly more difficult, as Perl is a	753	The mapping from Perl to JSON is slightly more difficult, as Perl is a
409	truly typeless language, so we can only guess which JSON type is meant by	754	truly typeless language, so we can only guess which JSON type is meant by
…		…
432	Other unblessed references are generally not allowed and will cause an	777	Other unblessed references are generally not allowed and will cause an
433	exception to be thrown, except for references to the integers C<0> and	778	exception to be thrown, except for references to the integers C<0> and
434	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	779	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
435	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.	780	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
436		781
437	to_json [\0,JSON::XS::true] # yields [false,true]	782	encode_json [\0,JSON::XS::true] # yields [false,true]
		783
		784	=item JSON::XS::true, JSON::XS::false
		785
		786	These special values become JSON true and JSON false values,
		787	respectively. You can also use C<\1> and C<\0> directly if you want.
438		788
439	=item blessed objects	789	=item blessed objects
440		790
441	Blessed objects are not allowed. JSON::XS currently tries to encode their	791	Blessed objects are not directly representable in JSON. See the
442	underlying representation (hash- or arrayref), but this behaviour might	792	C<allow_blessed> and C<convert_blessed> methods on various options on
443	change in future versions.	793	how to deal with this: basically, you can choose between throwing an
		794	exception, encoding the reference as if it weren't blessed, or provide
		795	your own serialiser method.
444		796
445	=item simple scalars	797	=item simple scalars
446		798
447	Simple Perl scalars (any scalar that is not a reference) are the most	799	Simple Perl scalars (any scalar that is not a reference) are the most
448	difficult objects to encode: JSON::XS will encode undefined scalars as	800	difficult objects to encode: JSON::XS will encode undefined scalars as
449	JSON null value, scalars that have last been used in a string context	801	JSON C<null> values, scalars that have last been used in a string context
450	before encoding as JSON strings and anything else as number value:	802	before encoding as JSON strings, and anything else as number value:
451		803
452	# dump as number	804	# dump as number
453	to_json [2] # yields [2]	805	encode_json [2] # yields [2]
454	to_json [-3.0e17] # yields [-3e+17]	806	encode_json [-3.0e17] # yields [-3e+17]
455	my $value = 5; to_json [$value] # yields [5]	807	my $value = 5; encode_json [$value] # yields [5]
456		808
457	# used as string, so dump as string	809	# used as string, so dump as string
458	print $value;	810	print $value;
459	to_json [$value] # yields ["5"]	811	encode_json [$value] # yields ["5"]
460		812
461	# undef becomes null	813	# undef becomes null
462	to_json [undef] # yields [null]	814	encode_json [undef] # yields [null]
463		815
464	You can force the type to be a string by stringifying it:	816	You can force the type to be a JSON string by stringifying it:
465		817
466	my $x = 3.1; # some variable containing a number	818	my $x = 3.1; # some variable containing a number
467	"$x"; # stringified	819	"$x"; # stringified
468	$x .= ""; # another, more awkward way to stringify	820	$x .= ""; # another, more awkward way to stringify
469	print $x; # perl does it for you, too, quite often	821	print $x; # perl does it for you, too, quite often
470		822
471	You can force the type to be a number by numifying it:	823	You can force the type to be a JSON number by numifying it:
472		824
473	my $x = "3"; # some variable containing a string	825	my $x = "3"; # some variable containing a string
474	$x += 0; # numify it, ensuring it will be dumped as a number	826	$x += 0; # numify it, ensuring it will be dumped as a number
475	$x *= 1; # same thing, the choise is yours.	827	$x *= 1; # same thing, the choice is yours.
476		828
477	You can not currently output JSON booleans or force the type in other,	829	You can not currently force the type in other, less obscure, ways. Tell me
478	less obscure, ways. Tell me if you need this capability.	830	if you need this capability (but don't forget to explain why it's needed
		831	:).
		832
		833	=back
		834
		835
		836	=head1 ENCODING/CODESET FLAG NOTES
		837
		838	The interested reader might have seen a number of flags that signify
		839	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		840	some confusion on what these do, so here is a short comparison:
		841
		842	C<utf8> controls whether the JSON text created by C<encode> (and expected
		843	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		844	control whether C<encode> escapes character values outside their respective
		845	codeset range. Neither of these flags conflict with each other, although
		846	some combinations make less sense than others.
		847
		848	Care has been taken to make all flags symmetrical with respect to
		849	C<encode> and C<decode>, that is, texts encoded with any combination of
		850	these flag values will be correctly decoded when the same flags are used
		851	- in general, if you use different flag settings while encoding vs. when
		852	decoding you likely have a bug somewhere.
		853
		854	Below comes a verbose discussion of these flags. Note that a "codeset" is
		855	simply an abstract set of character-codepoint pairs, while an encoding
		856	takes those codepoint numbers and I<encodes> them, in our case into
		857	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		858	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		859	the same time, which can be confusing.
		860
		861	=over 4
		862
		863	=item C<utf8> flag disabled
		864
		865	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		866	and expect Unicode strings, that is, characters with high ordinal Unicode
		867	values (> 255) will be encoded as such characters, and likewise such
		868	characters are decoded as-is, no canges to them will be done, except
		869	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		870	respectively (to Perl, these are the same thing in strings unless you do
		871	funny/weird/dumb stuff).
		872
		873	This is useful when you want to do the encoding yourself (e.g. when you
		874	want to have UTF-16 encoded JSON texts) or when some other layer does
		875	the encoding for you (for example, when printing to a terminal using a
		876	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		877	to UTF-8 encode your data first and have Perl encode it another time).
		878
		879	=item C<utf8> flag enabled
		880
		881	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		882	characters using the corresponding UTF-8 multi-byte sequence, and will
		883	expect your input strings to be encoded as UTF-8, that is, no "character"
		884	of the input string must have any value > 255, as UTF-8 does not allow
		885	that.
		886
		887	The C<utf8> flag therefore switches between two modes: disabled means you
		888	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		889	octet/binary string in Perl.
		890
		891	=item C<latin1> or C<ascii> flags enabled
		892
		893	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		894	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		895	characters as specified by the C<utf8> flag.
		896
		897	If C<utf8> is disabled, then the result is also correctly encoded in those
		898	character sets (as both are proper subsets of Unicode, meaning that a
		899	Unicode string with all character values < 256 is the same thing as a
		900	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		901	the same thing as an ASCII string in Perl).
		902
		903	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		904	regardless of these flags, just some more characters will be escaped using
		905	C<\uXXXX> then before.
		906
		907	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		908	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		909	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		910	a subset of Unicode), while ASCII is.
		911
		912	Surprisingly, C<decode> will ignore these flags and so treat all input
		913	values as governed by the C<utf8> flag. If it is disabled, this allows you
		914	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		915	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		916
		917	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		918	they only govern when the JSON output engine escapes a character or not.
		919
		920	The main use for C<latin1> is to relatively efficiently store binary data
		921	as JSON, at the expense of breaking compatibility with most JSON decoders.
		922
		923	The main use for C<ascii> is to force the output to not contain characters
		924	with values > 127, which means you can interpret the resulting string
		925	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		926	8-bit-encoding, and still get the same data structure back. This is useful
		927	when your channel for JSON transfer is not 8-bit clean or the encoding
		928	might be mangled in between (e.g. in mail), and works because ASCII is a
		929	proper subset of most 8-bit and multibyte encodings in use in the world.
479		930
480	=back	931	=back
481		932
482		933
483	=head1 COMPARISON	934	=head1 COMPARISON
…		…
488	followed by some benchmark values. JSON::XS was designed not to suffer	939	followed by some benchmark values. JSON::XS was designed not to suffer
489	from any of these problems or limitations.	940	from any of these problems or limitations.
490		941
491	=over 4	942	=over 4
492		943
		944	=item JSON 2.xx
		945
		946	A marvellous piece of engineering, this module either uses JSON::XS
		947	directly when available (so will be 100% compatible with it, including
		948	speed), or it uses JSON::PP, which is basically JSON::XS translated to
		949	Pure Perl, which should be 100% compatible with JSON::XS, just a bit
		950	slower.
		951
		952	You cannot really lose by using this module, especially as it tries very
		953	hard to work even with ancient Perl versions, while JSON::XS does not.
		954
493	=item JSON 1.07	955	=item JSON 1.07
494		956
495	Slow (but very portable, as it is written in pure Perl).	957	Slow (but very portable, as it is written in pure Perl).
496		958
497	Undocumented/buggy Unicode handling (how JSON handles unicode values is	959	Undocumented/buggy Unicode handling (how JSON handles Unicode values is
498	undocumented. One can get far by feeding it unicode strings and doing	960	undocumented. One can get far by feeding it Unicode strings and doing
499	en-/decoding oneself, but unicode escapes are not working properly).	961	en-/decoding oneself, but Unicode escapes are not working properly).
500		962
501	No roundtripping (strings get clobbered if they look like numbers, e.g.	963	No round-tripping (strings get clobbered if they look like numbers, e.g.
502	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	964	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
503	decode into the number 2.	965	decode into the number 2.
504		966
505	=item JSON::PC 0.01	967	=item JSON::PC 0.01
506		968
507	Very fast.	969	Very fast.
508		970
509	Undocumented/buggy Unicode handling.	971	Undocumented/buggy Unicode handling.
510		972
511	No roundtripping.	973	No round-tripping.
512		974
513	Has problems handling many Perl values (e.g. regex results and other magic	975	Has problems handling many Perl values (e.g. regex results and other magic
514	values will make it croak).	976	values will make it croak).
515		977
516	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	978	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
…		…
526	Very inflexible (no human-readable format supported, format pretty much	988	Very inflexible (no human-readable format supported, format pretty much
527	undocumented. I need at least a format for easy reading by humans and a	989	undocumented. I need at least a format for easy reading by humans and a
528	single-line compact format for use in a protocol, and preferably a way to	990	single-line compact format for use in a protocol, and preferably a way to
529	generate ASCII-only JSON texts).	991	generate ASCII-only JSON texts).
530		992
531	Completely broken (and confusingly documented) Unicode handling (unicode	993	Completely broken (and confusingly documented) Unicode handling (Unicode
532	escapes are not working properly, you need to set ImplicitUnicode to	994	escapes are not working properly, you need to set ImplicitUnicode to
533	I<different> values on en- and decoding to get symmetric behaviour).	995	I<different> values on en- and decoding to get symmetric behaviour).
534		996
535	No roundtripping (simple cases work, but this depends on wether the scalar	997	No round-tripping (simple cases work, but this depends on whether the scalar
536	value was used in a numeric context or not).	998	value was used in a numeric context or not).
537		999
538	Dumping hashes may skip hash values depending on iterator state.	1000	Dumping hashes may skip hash values depending on iterator state.
539		1001
540	Unmaintained (maintainer unresponsive for many months, bugs are not	1002	Unmaintained (maintainer unresponsive for many months, bugs are not
541	getting fixed).	1003	getting fixed).
542		1004
543	Does not check input for validity (i.e. will accept non-JSON input and	1005	Does not check input for validity (i.e. will accept non-JSON input and
544	return "something" instead of raising an exception. This is a security	1006	return "something" instead of raising an exception. This is a security
545	issue: imagine two banks transfering money between each other using	1007	issue: imagine two banks transferring money between each other using
546	JSON. One bank might parse a given non-JSON request and deduct money,	1008	JSON. One bank might parse a given non-JSON request and deduct money,
547	while the other might reject the transaction with a syntax error. While a	1009	while the other might reject the transaction with a syntax error. While a
548	good protocol will at least recover, that is extra unnecessary work and	1010	good protocol will at least recover, that is extra unnecessary work and
549	the transaction will still not succeed).	1011	the transaction will still not succeed).
550		1012
551	=item JSON::DWIW 0.04	1013	=item JSON::DWIW 0.04
552		1014
553	Very fast. Very natural. Very nice.	1015	Very fast. Very natural. Very nice.
554		1016
555	Undocumented unicode handling (but the best of the pack. Unicode escapes	1017	Undocumented Unicode handling (but the best of the pack. Unicode escapes
556	still don't get parsed properly).	1018	still don't get parsed properly).
557		1019
558	Very inflexible.	1020	Very inflexible.
559		1021
560	No roundtripping.	1022	No round-tripping.
561		1023
562	Does not generate valid JSON texts (key strings are often unquoted, empty keys	1024	Does not generate valid JSON texts (key strings are often unquoted, empty keys
563	result in nothing being output)	1025	result in nothing being output)
564		1026
565	Does not check input for validity.	1027	Does not check input for validity.
566		1028
567	=back	1029	=back
		1030
		1031
		1032	=head2 JSON and YAML
		1033
		1034	You often hear that JSON is a subset of YAML. This is, however, a mass
		1035	hysteria(*) and very far from the truth (as of the time of this writing),
		1036	so let me state it clearly: I<in general, there is no way to configure
		1037	JSON::XS to output a data structure as valid YAML> that works in all
		1038	cases.
		1039
		1040	If you really must use JSON::XS to generate YAML, you should use this
		1041	algorithm (subject to change in future versions):
		1042
		1043	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1044	my $yaml = $to_yaml->encode ($ref) . "\n";
		1045
		1046	This will I<usually> generate JSON texts that also parse as valid
		1047	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1048	lengths that JSON doesn't have and also has different and incompatible
		1049	unicode handling, so you should make sure that your hash keys are
		1050	noticeably shorter than the 1024 "stream characters" YAML allows and that
		1051	you do not have characters with codepoint values outside the Unicode BMP
		1052	(basic multilingual page). YAML also does not allow C<\/> sequences in
		1053	strings (which JSON::XS does not I<currently> generate, but other JSON
		1054	generators might).
		1055
		1056	There might be other incompatibilities that I am not aware of (or the YAML
		1057	specification has been changed yet again - it does so quite often). In
		1058	general you should not try to generate YAML with a JSON generator or vice
		1059	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1060	high that you will run into severe interoperability problems when you
		1061	least expect it.
		1062
		1063	=over 4
		1064
		1065	=item (*)
		1066
		1067	I have been pressured multiple times by Brian Ingerson (one of the
		1068	authors of the YAML specification) to remove this paragraph, despite him
		1069	acknowledging that the actual incompatibilities exist. As I was personally
		1070	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1071	educate people about these issues, so others do not run into the same
		1072	problem again and again. After this, Brian called me a (quote)I<complete
		1073	and worthless idiot>(unquote).
		1074
		1075	In my opinion, instead of pressuring and insulting people who actually
		1076	clarify issues with YAML and the wrong statements of some of its
		1077	proponents, I would kindly suggest reading the JSON spec (which is not
		1078	that difficult or long) and finally make YAML compatible to it, and
		1079	educating users about the changes, instead of spreading lies about the
		1080	real compatibility for many I<years> and trying to silence people who
		1081	point out that it isn't true.
		1082
		1083	=back
		1084
568		1085
569	=head2 SPEED	1086	=head2 SPEED
570		1087
571	It seems that JSON::XS is surprisingly fast, as shown in the following	1088	It seems that JSON::XS is surprisingly fast, as shown in the following
572	tables. They have been generated with the help of the C<eg/bench> program	1089	tables. They have been generated with the help of the C<eg/bench> program
573	in the JSON::XS distribution, to make it easy to compare on your own	1090	in the JSON::XS distribution, to make it easy to compare on your own
574	system.	1091	system.
575		1092
576	First comes a comparison between various modules using a very short JSON	1093	First comes a comparison between various modules using
577	string:	1094	a very short single-line JSON string (also available at
		1095	L<http://dist.schmorp.de/misc/json/short.json>).
578		1096
579	{"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null}	1097	{"method": "handleMessage", "params": ["user1", "we were just talking"], \
		1098	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
580		1099
581	It shows the number of encodes/decodes per second (JSON::XS uses the	1100	It shows the number of encodes/decodes per second (JSON::XS uses
582	functional interface, while JSON::XS/2 uses the OO interface with	1101	the functional interface, while JSON::XS/2 uses the OO interface
583	pretty-printing and hashkey sorting enabled). Higher is better:	1102	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
		1103	shrink). Higher is better:
584		1104
585	module \| encode \| decode \|	1105	module \| encode \| decode \|
586	-----------\|------------\|------------\|	1106	-----------\|------------\|------------\|
587	JSON \| 11488.516 \| 7823.035 \|	1107	JSON 1.x \| 4990.842 \| 4088.813 \|
588	JSON::DWIW \| 94708.054 \| 129094.260 \|	1108	JSON::DWIW \| 51653.990 \| 71575.154 \|
589	JSON::PC \| 63884.157 \| 128528.212 \|	1109	JSON::PC \| 65948.176 \| 74631.744 \|
590	JSON::Syck \| 34898.677 \| 42096.911 \|	1110	JSON::PP \| 8931.652 \| 3817.168 \|
591	JSON::XS \| 654027.064 \| 396423.669 \|	1111	JSON::Syck \| 24877.248 \| 27776.848 \|
592	JSON::XS/2 \| 371564.190 \| 371725.613 \|	1112	JSON::XS \| 388361.481 \| 227951.304 \|
		1113	JSON::XS/2 \| 227951.304 \| 218453.333 \|
		1114	JSON::XS/3 \| 338250.323 \| 218453.333 \|
		1115	Storable \| 16500.016 \| 135300.129 \|
593	-----------+------------+------------+	1116	-----------+------------+------------+
594		1117
595	That is, JSON::XS is more than six times faster than JSON::DWIW on	1118	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
596	encoding, more than three times faster on decoding, and about thirty times	1119	about three times faster on decoding, and over forty times faster
597	faster than JSON, even with pretty-printing and key sorting.	1120	than JSON, even with pretty-printing and key sorting. It also compares
		1121	favourably to Storable for small amounts of data.
598		1122
599	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1123	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
600	search API (http://nanoref.com/yahooapis/mgPdGg):	1124	search API (L<http://dist.schmorp.de/misc/json/long.json>).
601		1125
602	module \| encode \| decode \|	1126	module \| encode \| decode \|
603	-----------\|------------\|------------\|	1127	-----------\|------------\|------------\|
604	JSON \| 273.023 \| 44.674 \|	1128	JSON 1.x \| 55.260 \| 34.971 \|
605	JSON::DWIW \| 1089.383 \| 1145.704 \|	1129	JSON::DWIW \| 825.228 \| 1082.513 \|
606	JSON::PC \| 3097.419 \| 2393.921 \|	1130	JSON::PC \| 3571.444 \| 2394.829 \|
607	JSON::Syck \| 514.060 \| 843.053 \|	1131	JSON::PP \| 210.987 \| 32.574 \|
608	JSON::XS \| 6479.668 \| 3636.364 \|	1132	JSON::Syck \| 552.551 \| 787.544 \|
609	JSON::XS/2 \| 3774.221 \| 3599.124 \|	1133	JSON::XS \| 5780.463 \| 4854.519 \|
		1134	JSON::XS/2 \| 3869.998 \| 4798.975 \|
		1135	JSON::XS/3 \| 5862.880 \| 4798.975 \|
		1136	Storable \| 4445.002 \| 5235.027 \|
610	-----------+------------+------------+	1137	-----------+------------+------------+
611		1138
612	Again, JSON::XS leads by far.	1139	Again, JSON::XS leads by far (except for Storable which non-surprisingly
		1140	decodes faster).
613		1141
614	On large strings containing lots of high unicode characters, some modules	1142	On large strings containing lots of high Unicode characters, some modules
615	(such as JSON::PC) seem to decode faster than JSON::XS, but the result	1143	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
616	will be broken due to missing (or wrong) unicode handling. Others refuse	1144	will be broken due to missing (or wrong) Unicode handling. Others refuse
617	to decode or encode properly, so it was impossible to prepare a fair	1145	to decode or encode properly, so it was impossible to prepare a fair
618	comparison table for that case.	1146	comparison table for that case.
619		1147
620		1148
621	=head1 SECURITY CONSIDERATIONS	1149	=head1 SECURITY CONSIDERATIONS
…		…
627	any buffer overflows. Obviously, this module should ensure that and I am	1155	any buffer overflows. Obviously, this module should ensure that and I am
628	trying hard on making that true, but you never know.	1156	trying hard on making that true, but you never know.
629		1157
630	Second, you need to avoid resource-starving attacks. That means you should	1158	Second, you need to avoid resource-starving attacks. That means you should
631	limit the size of JSON texts you accept, or make sure then when your	1159	limit the size of JSON texts you accept, or make sure then when your
632	resources run out, thats just fine (e.g. by using a separate process that	1160	resources run out, that's just fine (e.g. by using a separate process that
633	can crash safely). The size of a JSON text in octets or characters is	1161	can crash safely). The size of a JSON text in octets or characters is
634	usually a good indication of the size of the resources required to decode	1162	usually a good indication of the size of the resources required to decode
635	it into a Perl structure.	1163	it into a Perl structure. While JSON::XS can check the size of the JSON
		1164	text, it might be too late when you already have it in memory, so you
		1165	might want to check the size before you accept the string.
636		1166
637	Third, JSON::XS recurses using the C stack when decoding objects and	1167	Third, JSON::XS recurses using the C stack when decoding objects and
638	arrays. The C stack is a limited resource: for instance, on my amd64	1168	arrays. The C stack is a limited resource: for instance, on my amd64
639	machine with 8MB of stack size I can decode around 180k nested arrays but	1169	machine with 8MB of stack size I can decode around 180k nested arrays but
640	only 14k nested JSON objects (due to perl itself recursing deeply on croak	1170	only 14k nested JSON objects (due to perl itself recursing deeply on croak
641	to free the temporary). If that is exceeded, the program crashes. to be	1171	to free the temporary). If that is exceeded, the program crashes. To be
642	conservative, the default nesting limit is set to 512. If your process	1172	conservative, the default nesting limit is set to 512. If your process
643	has a smaller stack, you should adjust this setting accordingly with the	1173	has a smaller stack, you should adjust this setting accordingly with the
644	C<max_depth> method.	1174	C<max_depth> method.
645		1175
646	And last but least, something else could bomb you that I forgot to think	1176	Something else could bomb you, too, that I forgot to think of. In that
647	of. In that case, you get to keep the pieces. I am always open for hints,	1177	case, you get to keep the pieces. I am always open for hints, though...
648	though...	1178
		1179	Also keep in mind that JSON::XS might leak contents of your Perl data
		1180	structures in its error messages, so when you serialise sensitive
		1181	information you might want to make sure that exceptions thrown by JSON::XS
		1182	will not end up in front of untrusted eyes.
		1183
		1184	If you are using JSON::XS to return packets to consumption
		1185	by JavaScript scripts in a browser you should have a look at
		1186	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1187	you are vulnerable to some common attack vectors (which really are browser
		1188	design bugs, but it is still you who will have to deal with it, as major
		1189	browser developers care only for features, not about getting security
		1190	right).
		1191
		1192
		1193	=head1 THREADS
		1194
		1195	This module is I<not> guaranteed to be thread safe and there are no
		1196	plans to change this until Perl gets thread support (as opposed to the
		1197	horribly slow so-called "threads" which are simply slow and bloated
		1198	process simulations - use fork, it's I<much> faster, cheaper, better).
		1199
		1200	(It might actually work, but you have been warned).
649		1201
650		1202
651	=head1 BUGS	1203	=head1 BUGS
652		1204
653	While the goal of this module is to be correct, that unfortunately does	1205	While the goal of this module is to be correct, that unfortunately does
654	not mean its bug-free, only that I think its design is bug-free. It is	1206	not mean it's bug-free, only that I think its design is bug-free. It is
655	still relatively early in its development. If you keep reporting bugs they	1207	still relatively early in its development. If you keep reporting bugs they
656	will be fixed swiftly, though.	1208	will be fixed swiftly, though.
657		1209
		1210	Please refrain from using rt.cpan.org or any other bug reporting
		1211	service. I put the contact address into my modules for a reason.
		1212
658	=cut	1213	=cut
659		1214
		1215	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
		1216	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
		1217
660	sub true() { \1 }	1218	sub true() { $true }
661	sub false() { \0 }	1219	sub false() { $false }
		1220
		1221	sub is_bool($) {
		1222	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
		1223	# or UNIVERSAL::isa $_[0], "JSON::Literal"
		1224	}
		1225
		1226	XSLoader::load "JSON::XS", $VERSION;
		1227
		1228	package JSON::XS::Boolean;
		1229
		1230	use overload
		1231	"0+" => sub { ${$_[0]} },
		1232	"++" => sub { $_[0] = ${$_[0]} + 1 },
		1233	"--" => sub { $_[0] = ${$_[0]} - 1 },
		1234	fallback => 1;
662		1235
663	1;	1236	1;
		1237
		1238	=head1 SEE ALSO
		1239
		1240	The F<json_xs> command line utility for quick experiments.
664		1241
665	=head1 AUTHOR	1242	=head1 AUTHOR
666		1243
667	Marc Lehmann <schmorp@schmorp.de>	1244	Marc Lehmann <schmorp@schmorp.de>
668	http://home.schmorp.de/	1245	http://home.schmorp.de/

Diff Legend

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

Comparing JSON-XS/XS.pm (file contents): Revision 1.32 by root, Thu Apr 12 07:25:29 2007 UTC vs. Revision 1.93 by root, Sat Mar 22 22:21:33 2008 UTC

Diff Legend

Comparing JSON-XS/XS.pm (file contents):
Revision 1.32 by root, Thu Apr 12 07:25:29 2007 UTC vs.
Revision 1.93 by root, Sat Mar 22 22:21:33 2008 UTC