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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.3 by root, Thu Mar 22 18:10:29 2007 UTC vs.
Revision 1.41 by root, Mon Jun 11 03:45:26 2007 UTC

…		…
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	3	JSON::XS - JSON serialising/deserialising, done correctly and fast
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use JSON::XS;	7	use JSON::XS;
		8
		9	# exported functions, they croak on error
		10	# and expect/generate UTF-8
		11
		12	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
		13	$perl_hash_or_arrayref = from_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	# OO-interface
		20
		21	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
		22	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
		23	$perl_scalar = $coder->decode ($unicode_json_text);
8		24
9	=head1 DESCRIPTION	25	=head1 DESCRIPTION
10		26
11	This module converts Perl data structures to JSON and vice versa. Its	27	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	28	primary goal is to be I<correct> and its secondary goal is to be
…		…
18	their maintainers are unresponsive, gone missing, or not listening to bug	34	their maintainers are unresponsive, gone missing, or not listening to bug
19	reports for other reasons.	35	reports for other reasons.
20		36
21	See COMPARISON, below, for a comparison to some other JSON modules.	37	See COMPARISON, below, for a comparison to some other JSON modules.
22		38
		39	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
		40	vice versa.
		41
23	=head2 FEATURES	42	=head2 FEATURES
24		43
25	=over 4	44	=over 4
26		45
27	=item * correct handling of unicode issues	46	=item * correct unicode handling
28		47
29	This module knows how to handle Unicode, and even documents how it does so.	48	This module knows how to handle Unicode, and even documents how and when
		49	it does so.
30		50
31	=item * round-trip integrity	51	=item * round-trip integrity
32		52
33	When you serialise a perl data structure using only datatypes supported	53	When you serialise a perl data structure using only datatypes supported
34	by JSON, the deserialised data structure is identical on the Perl level.	54	by JSON, the deserialised data structure is identical on the Perl level.
35	(e.g. the string "2.0" doesn't suddenly become "2").	55	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
		56	like a number).
36		57
37	=item * strict checking of JSON correctness	58	=item * strict checking of JSON correctness
38		59
39	There is no guessing, no generating of illegal JSON strings by default,	60	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).	61	and only JSON is accepted as input by default (the latter is a security
		62	feature).
41		63
42	=item * fast	64	=item * fast
43		65
44	compared to other JSON modules, this module compares favourably.	66	Compared to other JSON modules, this module compares favourably in terms
		67	of speed, too.
45		68
46	=item * simple to use	69	=item * simple to use
47		70
48	This module has both a simple functional interface as well as an OO	71	This module has both a simple functional interface as well as an OO
49	interface.	72	interface.
50		73
51	=item * reasonably versatile output formats	74	=item * reasonably versatile output formats
52		75
53	You can choose between the most compact format possible, a pure-ascii	76	You can choose between the most compact guarenteed single-line format
54	format, or a pretty-printed format. Or you can combine those features in	77	possible (nice for simple line-based protocols), a pure-ascii format
55	whatever way you like.	78	(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
		80	stuff). Or you can combine those features in whatever way you like.
56		81
57	=back	82	=back
58		83
59	=cut	84	=cut
60		85
61	package JSON::XS;	86	package JSON::XS;
62		87
		88	use strict;
		89
63	BEGIN {	90	BEGIN {
64	$VERSION = '0.1';	91	our $VERSION = '1.24';
65	@ISA = qw(Exporter);	92	our @ISA = qw(Exporter);
66		93
67	@EXPORT = qw(to_json from_json);	94	our @EXPORT = qw(to_json from_json objToJson jsonToObj);
68	require Exporter;	95	require Exporter;
69		96
70	require XSLoader;	97	require XSLoader;
71	XSLoader::load JSON::XS::, $VERSION;	98	XSLoader::load JSON::XS::, $VERSION;
72	}	99	}
…		…
76	The following convinience methods are provided by this module. They are	103	The following convinience methods are provided by this module. They are
77	exported by default:	104	exported by default:
78		105
79	=over 4	106	=over 4
80		107
81	=item $json_string = to_json $perl_scalar	108	=item $json_text = to_json $perl_scalar
82		109
83	Converts the given Perl data structure (a simple scalar or a reference to	110	Converts the given Perl data structure (a simple scalar or a reference to
84	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	111	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains
85	octets only). Croaks on error.	112	octets only). Croaks on error.
86		113
87	This function call is functionally identical to C<< JSON::XS->new->utf8	114	This function call is functionally identical to:
88	(1)->encode ($perl_scalar) >>.
89		115
		116	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
		117
		118	except being faster.
		119
90	=item $perl_scalar = from_json $json_string	120	=item $perl_scalar = from_json $json_text
91		121
92	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	122	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to
93	parse that as an UTF-8 encoded JSON string, returning the resulting simple	123	parse that as an UTF-8 encoded JSON text, returning the resulting simple
94	scalar or reference. Croaks on error.	124	scalar or reference. Croaks on error.
95		125
96	This function call is functionally identical to C<< JSON::XS->new->utf8	126	This function call is functionally identical to:
97	(1)->decode ($json_string) >>.	127
		128	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
		129
		130	except being faster.
98		131
99	=back	132	=back
		133
100		134
101	=head1 OBJECT-ORIENTED INTERFACE	135	=head1 OBJECT-ORIENTED INTERFACE
102		136
103	The object oriented interface lets you configure your own encoding or	137	The object oriented interface lets you configure your own encoding or
104	decoding style, within the limits of supported formats.	138	decoding style, within the limits of supported formats.
…		…
111	strings. All boolean flags described below are by default I<disabled>.	145	strings. All boolean flags described below are by default I<disabled>.
112		146
113	The mutators for flags all return the JSON object again and thus calls can	147	The mutators for flags all return the JSON object again and thus calls can
114	be chained:	148	be chained:
115		149
116	my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]})	150	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
117	=> {"a": [1, 2]}	151	=> {"a": [1, 2]}
118		152
119	=item $json = $json->ascii ($enable)	153	=item $json = $json->ascii ([$enable])
120		154
121	If C<$enable> is true, then the C<encode> method will not generate	155	If C<$enable> is true (or missing), then the C<encode> method will not
122	characters outside the code range C<0..127>. Any unicode characters	156	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	157	unicode characters outside that range will be escaped using either a
124	characters) or a double \uHHHH\uLLLLL escape sequence, as per RFC4627.	158	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
		160	unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		161	or any other superset of ASCII.
125		162
126	If C<$enable> is false, then the C<encode> method will not escape Unicode	163	If C<$enable> is false, then the C<encode> method will not escape Unicode
127	characters unless necessary.	164	characters unless required by the JSON syntax or other flags. This results
		165	in a faster and more compact format.
128		166
		167	The main use for this flag is to produce JSON texts that can be
		168	transmitted over a 7-bit channel, as the encoded JSON texts will not
		169	contain any 8 bit characters.
		170
129	JSON::XS->new->ascii (1)->encode (chr 0x10401)	171	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
130	=> \ud801\udc01	172	=> ["\ud801\udc01"]
131		173
		174	=item $json = $json->latin1 ([$enable])
		175
		176	If C<$enable> is true (or missing), then the C<encode> method will encode
		177	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		178	outside the code range C<0..255>. The resulting string can be treated as a
		179	latin1-encoded JSON text or a native unicode string. The C<decode> method
		180	will not be affected in any way by this flag, as C<decode> by default
		181	expects unicode, which is a strict superset of latin1.
		182
		183	If C<$enable> is false, then the C<encode> method will not escape Unicode
		184	characters unless required by the JSON syntax or other flags.
		185
		186	The main use for this flag is efficiently encoding binary data as JSON
		187	text, as most octets will not be escaped, resulting in a smaller encoded
		188	size. The disadvantage is that the resulting JSON text is encoded
		189	in latin1 (and must correctly be treated as such when storing and
		190	transfering), a rare encoding for JSON. It is therefore most useful when
		191	you want to store data structures known to contain binary data efficiently
		192	in files or databases, not when talking to other JSON encoders/decoders.
		193
		194	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		195	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
		196
132	=item $json = $json->utf8 ($enable)	197	=item $json = $json->utf8 ([$enable])
133		198
134	If C<$enable> is true, then the C<encode> method will encode the JSON	199	If C<$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>	200	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	201	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	202	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.	203	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
		204	versions, enabling this option might enable autodetection of the UTF-16
		205	and UTF-32 encoding families, as described in RFC4627.
139		206
140	If C<$enable> is false, then the C<encode> method will return the JSON	207	If C<$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	208	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	209	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.	210	to be done yourself, e.g. using the Encode module.
144		211
		212	Example, output UTF-16BE-encoded JSON:
		213
		214	use Encode;
		215	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
		216
		217	Example, decode UTF-32LE-encoded JSON:
		218
		219	use Encode;
		220	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
		221
145	=item $json = $json->pretty ($enable)	222	=item $json = $json->pretty ([$enable])
146		223
147	This enables (or disables) all of the C<indent>, C<space_before> and	224	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	225	C<space_after> (and in the future possibly more) flags in one call to
149	generate the most readable (or most compact) form possible.	226	generate the most readable (or most compact) form possible.
		227
		228	Example, pretty-print some simple structure:
150		229
151	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})	230	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
152	=>	231	=>
153	{	232	{
154	"a" : [	233	"a" : [
155	1,	234	1,
156	2	235	2
157	]	236	]
158	}	237	}
159		238
160	=item $json = $json->indent ($enable)	239	=item $json = $json->indent ([$enable])
161		240
162	If C<$enable> is true, then the C<encode> method will use a multiline	241	If C<$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	242	format as output, putting every array member or object/hash key-value pair
164	into its own line, identing them properly.	243	into its own line, identing them properly.
165		244
166	If C<$enable> is false, no newlines or indenting will be produced, and the	245	If C<$enable> is false, no newlines or indenting will be produced, and the
167	resulting JSON strings is guarenteed not to contain any C<newlines>.	246	resulting JSON text is guarenteed not to contain any C<newlines>.
168		247
169	This setting has no effect when decoding JSON strings.	248	This setting has no effect when decoding JSON texts.
170		249
171	=item $json = $json->space_before ($enable)	250	=item $json = $json->space_before ([$enable])
172		251
173	If C<$enable> is true, then the C<encode> method will add an extra	252	If C<$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.	253	optional space before the C<:> separating keys from values in JSON objects.
175		254
176	If C<$enable> is false, then the C<encode> method will not add any extra	255	If C<$enable> is false, then the C<encode> method will not add any extra
177	space at those places.	256	space at those places.
178		257
179	This setting has no effect when decoding JSON strings. You will also most	258	This setting has no effect when decoding JSON texts. You will also
180	likely combine this setting with C<space_after>.	259	most likely combine this setting with C<space_after>.
181		260
		261	Example, space_before enabled, space_after and indent disabled:
		262
		263	{"key" :"value"}
		264
182	=item $json = $json->space_after ($enable)	265	=item $json = $json->space_after ([$enable])
183		266
184	If C<$enable> is true, then the C<encode> method will add an extra	267	If C<$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	268	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	269	and extra whitespace after the C<,> separating key-value pairs and array
187	members.	270	members.
188		271
189	If C<$enable> is false, then the C<encode> method will not add any extra	272	If C<$enable> is false, then the C<encode> method will not add any extra
190	space at those places.	273	space at those places.
191		274
192	This setting has no effect when decoding JSON strings.	275	This setting has no effect when decoding JSON texts.
193		276
		277	Example, space_before and indent disabled, space_after enabled:
		278
		279	{"key": "value"}
		280
194	=item $json = $json->canonical ($enable)	281	=item $json = $json->canonical ([$enable])
195		282
196	If C<$enable> is true, then the C<encode> method will output JSON objects	283	If C<$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.	284	by sorting their keys. This is adding a comparatively high overhead.
198		285
199	If C<$enable> is false, then the C<encode> method will output key-value	286	If C<$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	287	pairs in the order Perl stores them (which will likely change between runs
201	of the same script).	288	of the same script).
202		289
203	This option is useful if you want the same data structure to be encoded as	290	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,	291	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,	292	the same hash migh be encoded differently even if contains the same data,
206	as key-value pairs have no inherent ordering in Perl.	293	as key-value pairs have no inherent ordering in Perl.
207		294
208	This setting has no effect when decoding JSON strings.	295	This setting has no effect when decoding JSON texts.
209		296
210	=item $json = $json->allow_nonref ($enable)	297	=item $json = $json->allow_nonref ([$enable])
211		298
212	If C<$enable> is true, then the C<encode> method can convert a	299	If C<$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,	300	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	301	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
215	values instead of croaking.	302	values instead of croaking.
216		303
217	If C<$enable> is false, then the C<encode> method will croak if it isn't	304	If C<$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	305	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	306	or array. Likewise, C<decode> will croak if given something that is not a
220	JSON object or array.	307	JSON object or array.
221		308
		309	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
		310	resulting in an invalid JSON text:
		311
		312	JSON::XS->new->allow_nonref->encode ("Hello, World!")
		313	=> "Hello, World!"
		314
		315	=item $json = $json->shrink ([$enable])
		316
		317	Perl usually over-allocates memory a bit when allocating space for
		318	strings. This flag optionally resizes strings generated by either
		319	C<encode> or C<decode> to their minimum size possible. This can save
		320	memory when your JSON texts are either very very long or you have many
		321	short strings. It will also try to downgrade any strings to octet-form
		322	if possible: perl stores strings internally either in an encoding called
		323	UTF-X or in octet-form. The latter cannot store everything but uses less
		324	space in general (and some buggy Perl or C code might even rely on that
		325	internal representation being used).
		326
		327	The actual definition of what shrink does might change in future versions,
		328	but it will always try to save space at the expense of time.
		329
		330	If C<$enable> is true (or missing), the string returned by C<encode> will
		331	be shrunk-to-fit, while all strings generated by C<decode> will also be
		332	shrunk-to-fit.
		333
		334	If C<$enable> is false, then the normal perl allocation algorithms are used.
		335	If you work with your data, then this is likely to be faster.
		336
		337	In the future, this setting might control other things, such as converting
		338	strings that look like integers or floats into integers or floats
		339	internally (there is no difference on the Perl level), saving space.
		340
		341	=item $json = $json->max_depth ([$maximum_nesting_depth])
		342
		343	Sets the maximum nesting level (default C<512>) accepted while encoding
		344	or decoding. If the JSON text or Perl data structure has an equal or
		345	higher nesting level then this limit, then the encoder and decoder will
		346	stop and croak at that point.
		347
		348	Nesting level is defined by number of hash- or arrayrefs that the encoder
		349	needs to traverse to reach a given point or the number of C<{> or C<[>
		350	characters without their matching closing parenthesis crossed to reach a
		351	given character in a string.
		352
		353	Setting the maximum depth to one disallows any nesting, so that ensures
		354	that the object is only a single hash/object or array.
		355
		356	The argument to C<max_depth> will be rounded up to the next nearest power
		357	of two.
		358
		359	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		360
222	=item $json_string = $json->encode ($perl_scalar)	361	=item $json_text = $json->encode ($perl_scalar)
223		362
224	Converts the given Perl data structure (a simple scalar or a reference	363	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	364	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	365	converted into JSON string or number sequences, while references to arrays
227	become JSON arrays and references to hashes become JSON objects. Undefined	366	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>	367	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
229	nor C<false> values will be generated.	368	nor C<false> values will be generated.
230		369
231	=item $perl_scalar = $json->decode ($json_string)	370	=item $perl_scalar = $json->decode ($json_text)
232		371
233	The opposite of C<encode>: expects a JSON string and tries to parse it,	372	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.	373	returning the resulting simple scalar or reference. Croaks on error.
235		374
236	JSON numbers and strings become simple Perl scalars. JSON arrays become	375	JSON numbers and strings become simple Perl scalars. JSON arrays become
237	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	376	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>.	377	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
239		378
		379	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		380
		381	This works like the C<decode> method, but instead of raising an exception
		382	when there is trailing garbage after the first JSON object, it will
		383	silently stop parsing there and return the number of characters consumed
		384	so far.
		385
		386	This is useful if your JSON texts are not delimited by an outer protocol
		387	(which is not the brightest thing to do in the first place) and you need
		388	to know where the JSON text ends.
		389
		390	JSON::XS->new->decode_prefix ("[1] the tail")
		391	=> ([], 3)
		392
240	=back	393	=back
		394
		395
		396	=head1 MAPPING
		397
		398	This section describes how JSON::XS maps Perl values to JSON values and
		399	vice versa. These mappings are designed to "do the right thing" in most
		400	circumstances automatically, preserving round-tripping characteristics
		401	(what you put in comes out as something equivalent).
		402
		403	For the more enlightened: note that in the following descriptions,
		404	lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>
		405	refers to the abstract Perl language itself.
		406
		407
		408	=head2 JSON -> PERL
		409
		410	=over 4
		411
		412	=item object
		413
		414	A JSON object becomes a reference to a hash in Perl. No ordering of object
		415	keys is preserved (JSON does not preserver object key ordering itself).
		416
		417	=item array
		418
		419	A JSON array becomes a reference to an array in Perl.
		420
		421	=item string
		422
		423	A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON
		424	are represented by the same codepoints in the Perl string, so no manual
		425	decoding is necessary.
		426
		427	=item number
		428
		429	A JSON number becomes either an integer or numeric (floating point)
		430	scalar in perl, depending on its range and any fractional parts. On the
		431	Perl level, there is no difference between those as Perl handles all the
		432	conversion details, but an integer may take slightly less memory and might
		433	represent more values exactly than (floating point) numbers.
		434
		435	=item true, false
		436
		437	These JSON atoms become C<0>, C<1>, respectively. Information is lost in
		438	this process. Future versions might represent those values differently,
		439	but they will be guarenteed to act like these integers would normally in
		440	Perl.
		441
		442	=item null
		443
		444	A JSON null atom becomes C<undef> in Perl.
		445
		446	=back
		447
		448
		449	=head2 PERL -> JSON
		450
		451	The mapping from Perl to JSON is slightly more difficult, as Perl is a
		452	truly typeless language, so we can only guess which JSON type is meant by
		453	a Perl value.
		454
		455	=over 4
		456
		457	=item hash references
		458
		459	Perl hash references become JSON objects. As there is no inherent ordering
		460	in hash keys (or JSON objects), they will usually be encoded in a
		461	pseudo-random order that can change between runs of the same program but
		462	stays generally the same within a single run of a program. JSON::XS can
		463	optionally sort the hash keys (determined by the I<canonical> flag), so
		464	the same datastructure will serialise to the same JSON text (given same
		465	settings and version of JSON::XS), but this incurs a runtime overhead
		466	and is only rarely useful, e.g. when you want to compare some JSON text
		467	against another for equality.
		468
		469	=item array references
		470
		471	Perl array references become JSON arrays.
		472
		473	=item other references
		474
		475	Other unblessed references are generally not allowed and will cause an
		476	exception to be thrown, except for references to the integers C<0> and
		477	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
		478	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
		479
		480	to_json [\0,JSON::XS::true] # yields [false,true]
		481
		482	=item blessed objects
		483
		484	Blessed objects are not allowed. JSON::XS currently tries to encode their
		485	underlying representation (hash- or arrayref), but this behaviour might
		486	change in future versions.
		487
		488	=item simple scalars
		489
		490	Simple Perl scalars (any scalar that is not a reference) are the most
		491	difficult objects to encode: JSON::XS will encode undefined scalars as
		492	JSON null value, scalars that have last been used in a string context
		493	before encoding as JSON strings and anything else as number value:
		494
		495	# dump as number
		496	to_json [2] # yields [2]
		497	to_json [-3.0e17] # yields [-3e+17]
		498	my $value = 5; to_json [$value] # yields [5]
		499
		500	# used as string, so dump as string
		501	print $value;
		502	to_json [$value] # yields ["5"]
		503
		504	# undef becomes null
		505	to_json [undef] # yields [null]
		506
		507	You can force the type to be a string by stringifying it:
		508
		509	my $x = 3.1; # some variable containing a number
		510	"$x"; # stringified
		511	$x .= ""; # another, more awkward way to stringify
		512	print $x; # perl does it for you, too, quite often
		513
		514	You can force the type to be a number by numifying it:
		515
		516	my $x = "3"; # some variable containing a string
		517	$x += 0; # numify it, ensuring it will be dumped as a number
		518	$x *= 1; # same thing, the choise is yours.
		519
		520	You can not currently output JSON booleans or force the type in other,
		521	less obscure, ways. Tell me if you need this capability.
		522
		523	=back
		524
241		525
242	=head1 COMPARISON	526	=head1 COMPARISON
243		527
244	As already mentioned, this module was created because none of the existing	528	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	529	JSON modules could be made to work correctly. First I will describe the
246	problems (or pleasures) I encountered with various existing JSON modules,	530	problems (or pleasures) I encountered with various existing JSON modules,
247	followed by some benchmark values.	531	followed by some benchmark values. JSON::XS was designed not to suffer
		532	from any of these problems or limitations.
248		533
249	=over 4	534	=over 4
250		535
251	=item JSON	536	=item JSON 1.07
252		537
253	Slow (but very portable, as it is written in pure Perl).	538	Slow (but very portable, as it is written in pure Perl).
254		539
255	Undocumented/buggy Unicode handling (how JSON handles unicode values is	540	Undocumented/buggy Unicode handling (how JSON handles unicode values is
256	undocumented. One can get far by feeding it unicode strings and doing	541	undocumented. One can get far by feeding it unicode strings and doing
…		…
258		543
259	No roundtripping (strings get clobbered if they look like numbers, e.g.	544	No roundtripping (strings get clobbered if they look like numbers, e.g.
260	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	545	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
261	decode into the number 2.	546	decode into the number 2.
262		547
263	=item JSON::PC	548	=item JSON::PC 0.01
264		549
265	Very fast.	550	Very fast.
		551
		552	Undocumented/buggy Unicode handling.
		553
		554	No roundtripping.
		555
		556	Has problems handling many Perl values (e.g. regex results and other magic
		557	values will make it croak).
		558
		559	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
		560	which is not a valid JSON text.
		561
		562	Unmaintained (maintainer unresponsive for many months, bugs are not
		563	getting fixed).
		564
		565	=item JSON::Syck 0.21
		566
		567	Very buggy (often crashes).
266		568
267	Very inflexible (no human-readable format supported, format pretty much	569	Very inflexible (no human-readable format supported, format pretty much
268	undocumented. I need at least a format for easy reading by humans and a	570	undocumented. I need at least a format for easy reading by humans and a
269	single-line compact format for use in a protocol, and preferably a way to	571	single-line compact format for use in a protocol, and preferably a way to
270	generate ASCII-only JSON strings).	572	generate ASCII-only JSON texts).
271
272	Undocumented/buggy Unicode handling.
273
274	No roundtripping.
275
276	Has problems handling many Perl values.
277
278	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
279	which is not a valid JSON string.
280
281	Unmaintained (maintainer unresponsive for many months, bugs are not
282	getting fixed).
283
284	=item JSON::Syck
285
286	Very buggy (often crashes).
287
288	Very inflexible.
289		573
290	Completely broken (and confusingly documented) Unicode handling (unicode	574	Completely broken (and confusingly documented) Unicode handling (unicode
291	escapes are not working properly, you need to set ImplicitUnicode to	575	escapes are not working properly, you need to set ImplicitUnicode to
292	I<different> values on en- and decoding to get symmetric behaviour).	576	I<different> values on en- and decoding to get symmetric behaviour).
293		577
…		…
305	JSON. One bank might parse a given non-JSON request and deduct money,	589	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	590	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	591	good protocol will at least recover, that is extra unnecessary work and
308	the transaction will still not succeed).	592	the transaction will still not succeed).
309		593
310	=item JSON::DWIW	594	=item JSON::DWIW 0.04
311		595
312	Very fast. Very natural. Very nice.	596	Very fast. Very natural. Very nice.
313		597
314	Undocumented unicode handling (but the best of the pack. Unicode escapes	598	Undocumented unicode handling (but the best of the pack. Unicode escapes
315	still don't get parsed properly).	599	still don't get parsed properly).
316		600
317	Very inflexible.	601	Very inflexible.
318		602
319	No roundtripping.	603	No roundtripping.
320		604
		605	Does not generate valid JSON texts (key strings are often unquoted, empty keys
		606	result in nothing being output)
		607
321	Does not check input for validity.	608	Does not check input for validity.
322		609
323	=back	610	=back
324		611
		612
		613	=head2 JSON and YAML
		614
		615	You often hear that JSON is a subset (or a close subset) of YAML. This is,
		616	however, a mass hysteria and very far from the truth. In general, there is
		617	no way to configure JSON::XS to output a data structure as valid YAML.
		618
		619	If you really must use JSON::XS to generate YAML, you should use this
		620	algorithm (subject to change in future versions):
		621
		622	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		623	my $yaml = $to_yaml->encode ($ref) . "\n";
		624
		625	This will usually generate JSON texts that also parse as valid
		626	YAML. Please note that YAML has hardcoded limits on (simple) object key
		627	lengths that JSON doesn't have, so you should make sure that your hash
		628	keys are noticably shorter than the 1024 characters YAML allows.
		629
		630	There might be other incompatibilities that I am not aware of. In general
		631	you should not try to generate YAML with a JSON generator or vice versa,
		632	or try to parse JSON with a YAML parser or vice versa: chances are high
		633	that you will run into severe interoperability problems.
		634
		635
325	=head2 SPEED	636	=head2 SPEED
326		637
		638	It seems that JSON::XS is surprisingly fast, as shown in the following
		639	tables. They have been generated with the help of the C<eg/bench> program
		640	in the JSON::XS distribution, to make it easy to compare on your own
		641	system.
		642
		643	First comes a comparison between various modules using a very short
		644	single-line JSON string:
		645
		646	{"method": "handleMessage", "params": ["user1", "we were just talking"], \
		647	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
		648
		649	It shows the number of encodes/decodes per second (JSON::XS uses
		650	the functional interface, while JSON::XS/2 uses the OO interface
		651	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
		652	shrink). Higher is better:
		653
		654	module \| encode \| decode \|
		655	-----------\|------------\|------------\|
		656	JSON \| 7645.468 \| 4208.613 \|
		657	JSON::DWIW \| 40721.398 \| 77101.176 \|
		658	JSON::PC \| 65948.176 \| 78251.940 \|
		659	JSON::Syck \| 22844.793 \| 26479.192 \|
		660	JSON::XS \| 388361.481 \| 199728.762 \|
		661	JSON::XS/2 \| 218453.333 \| 192399.266 \|
		662	JSON::XS/3 \| 338250.323 \| 192399.266 \|
		663	Storable \| 15779.925 \| 14169.946 \|
		664	-----------+------------+------------+
		665
		666	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
		667	about three times faster on decoding, and over fourty times faster
		668	than JSON, even with pretty-printing and key sorting. It also compares
		669	favourably to Storable for small amounts of data.
		670
		671	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
		672	search API (http://nanoref.com/yahooapis/mgPdGg):
		673
		674	module \| encode \| decode \|
		675	-----------\|------------\|------------\|
		676	JSON \| 254.685 \| 37.665 \|
		677	JSON::DWIW \| 843.343 \| 1049.731 \|
		678	JSON::PC \| 3602.116 \| 2307.352 \|
		679	JSON::Syck \| 505.107 \| 787.899 \|
		680	JSON::XS \| 5747.196 \| 3690.220 \|
		681	JSON::XS/2 \| 3968.121 \| 3676.634 \|
		682	JSON::XS/3 \| 6105.246 \| 3662.508 \|
		683	Storable \| 4417.337 \| 5285.161 \|
		684	-----------+------------+------------+
		685
		686	Again, JSON::XS leads by far (except for Storable which non-surprisingly
		687	decodes faster).
		688
		689	On large strings containing lots of high unicode characters, some modules
		690	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
		691	will be broken due to missing (or wrong) unicode handling. Others refuse
		692	to decode or encode properly, so it was impossible to prepare a fair
		693	comparison table for that case.
		694
		695
		696	=head1 SECURITY CONSIDERATIONS
		697
		698	When you are using JSON in a protocol, talking to untrusted potentially
		699	hostile creatures requires relatively few measures.
		700
		701	First of all, your JSON decoder should be secure, that is, should not have
		702	any buffer overflows. Obviously, this module should ensure that and I am
		703	trying hard on making that true, but you never know.
		704
		705	Second, you need to avoid resource-starving attacks. That means you should
		706	limit the size of JSON texts you accept, or make sure then when your
		707	resources run out, thats just fine (e.g. by using a separate process that
		708	can crash safely). The size of a JSON text in octets or characters is
		709	usually a good indication of the size of the resources required to decode
		710	it into a Perl structure.
		711
		712	Third, JSON::XS recurses using the C stack when decoding objects and
		713	arrays. The C stack is a limited resource: for instance, on my amd64
		714	machine with 8MB of stack size I can decode around 180k nested arrays but
		715	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		716	to free the temporary). If that is exceeded, the program crashes. to be
		717	conservative, the default nesting limit is set to 512. If your process
		718	has a smaller stack, you should adjust this setting accordingly with the
		719	C<max_depth> method.
		720
		721	And last but least, something else could bomb you that I forgot to think
		722	of. In that case, you get to keep the pieces. I am always open for hints,
		723	though...
		724
		725
		726	=head1 BUGS
		727
		728	While the goal of this module is to be correct, that unfortunately does
		729	not mean its bug-free, only that I think its design is bug-free. It is
		730	still relatively early in its development. If you keep reporting bugs they
		731	will be fixed swiftly, though.
		732
327	=cut	733	=cut
		734
		735	sub true() { \1 }
		736	sub false() { \0 }
328		737
329	1;	738	1;
330		739
331	=head1 AUTHOR	740	=head1 AUTHOR
332		741

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Revision 1.41 by root, Mon Jun 11 03:45:26 2007 UTC