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Revision 1.51 by root, Mon Jul 2 01:12:27 2007 UTC vs.
Revision 1.103 by root, Tue Apr 29 16:07:56 2008 UTC

1=head1 NAME 1=head1 NAME
2 2
3JSON::XS - JSON serialising/deserialising, done correctly and fast 3JSON::XS - JSON serialising/deserialising, done correctly and fast
4
5=encoding utf-8
6
7JSON::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 19
15 # OO-interface 20 # OO-interface
16 21
17 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 22 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
18 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 23 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
19 $perl_scalar = $coder->decode ($unicode_json_text); 24 $perl_scalar = $coder->decode ($unicode_json_text);
20 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
21=head1 DESCRIPTION 34=head1 DESCRIPTION
22 35
23This module converts Perl data structures to JSON and vice versa. Its 36This module converts Perl data structures to JSON and vice versa. Its
24primary goal is to be I<correct> and its secondary goal is to be 37primary goal is to be I<correct> and its secondary goal is to be
25I<fast>. To reach the latter goal it was written in C. 38I<fast>. To reach the latter goal it was written in C.
39
40Beginning with version 2.0 of the JSON module, when both JSON and
41JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
42overriden) with no overhead due to emulation (by inheritign constructor
43and methods). If JSON::XS is not available, it will fall back to the
44compatible JSON::PP module as backend, so using JSON instead of JSON::XS
45gives you a portable JSON API that can be fast when you need and doesn't
46require a C compiler when that is a problem.
26 47
27As this is the n-th-something JSON module on CPAN, what was the reason 48As this is the n-th-something JSON module on CPAN, what was the reason
28to write yet another JSON module? While it seems there are many JSON 49to write yet another JSON module? While it seems there are many JSON
29modules, none of them correctly handle all corner cases, and in most cases 50modules, none of them correctly handle all corner cases, and in most cases
30their maintainers are unresponsive, gone missing, or not listening to bug 51their maintainers are unresponsive, gone missing, or not listening to bug
37 58
38=head2 FEATURES 59=head2 FEATURES
39 60
40=over 4 61=over 4
41 62
42=item * correct unicode handling 63=item * correct Unicode handling
43 64
44This module knows how to handle Unicode, and even documents how and when 65This module knows how to handle Unicode, documents how and when it does
45it does so. 66so, and even documents what "correct" means.
46 67
47=item * round-trip integrity 68=item * round-trip integrity
48 69
49When you serialise a perl data structure using only datatypes supported 70When you serialise a perl data structure using only datatypes supported
50by JSON, the deserialised data structure is identical on the Perl level. 71by JSON, the deserialised data structure is identical on the Perl level.
51(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
52like a number). 73like a number). There minor I<are> exceptions to this, read the MAPPING
74section below to learn about those.
53 75
54=item * strict checking of JSON correctness 76=item * strict checking of JSON correctness
55 77
56There is no guessing, no generating of illegal JSON texts by default, 78There is no guessing, no generating of illegal JSON texts by default,
57and only JSON is accepted as input by default (the latter is a security 79and only JSON is accepted as input by default (the latter is a security
58feature). 80feature).
59 81
60=item * fast 82=item * fast
61 83
62Compared to other JSON modules, this module compares favourably in terms 84Compared to other JSON modules and other serialisers such as Storable,
63of speed, too. 85this module usually compares favourably in terms of speed, too.
64 86
65=item * simple to use 87=item * simple to use
66 88
67This module has both a simple functional interface as well as an OO 89This module has both a simple functional interface as well as an objetc
68interface. 90oriented interface interface.
69 91
70=item * reasonably versatile output formats 92=item * reasonably versatile output formats
71 93
72You can choose between the most compact guarenteed single-line format 94You can choose between the most compact guaranteed-single-line format
73possible (nice for simple line-based protocols), a pure-ascii format 95possible (nice for simple line-based protocols), a pure-ascii format
74(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
75unicode range), or a pretty-printed format (for when you want to read that 97Unicode range), or a pretty-printed format (for when you want to read that
76stuff). Or you can combine those features in whatever way you like. 98stuff). Or you can combine those features in whatever way you like.
77 99
78=back 100=back
79 101
80=cut 102=cut
81 103
82package JSON::XS; 104package JSON::XS;
83 105
84use strict; 106use strict;
85 107
86our $VERSION = '1.4'; 108our $VERSION = '2.2';
87our @ISA = qw(Exporter); 109our @ISA = qw(Exporter);
88 110
89our @EXPORT = qw(to_json from_json); 111our @EXPORT = qw(encode_json decode_json to_json from_json);
112
113sub to_json($) {
114 require Carp;
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");
116}
117
118sub 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}
90 122
91use Exporter; 123use Exporter;
92use XSLoader; 124use XSLoader;
93 125
94=head1 FUNCTIONAL INTERFACE 126=head1 FUNCTIONAL INTERFACE
95 127
96The following convinience methods are provided by this module. They are 128The following convenience methods are provided by this module. They are
97exported by default: 129exported by default:
98 130
99=over 4 131=over 4
100 132
101=item $json_text = to_json $perl_scalar 133=item $json_text = encode_json $perl_scalar
102 134
103Converts the given Perl data structure (a simple scalar or a reference to 135Converts the given Perl data structure to a UTF-8 encoded, binary string
104a 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.
105octets only). Croaks on error.
106 137
107This function call is functionally identical to: 138This function call is functionally identical to:
108 139
109 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 140 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
110 141
111except being faster. 142except being faster.
112 143
113=item $perl_scalar = from_json $json_text 144=item $perl_scalar = decode_json $json_text
114 145
115The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to 146The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
116parse that as an UTF-8 encoded JSON text, returning the resulting simple 147to parse that as an UTF-8 encoded JSON text, returning the resulting
117scalar or reference. Croaks on error. 148reference. Croaks on error.
118 149
119This function call is functionally identical to: 150This function call is functionally identical to:
120 151
121 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 152 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
122 153
132Perl. 163Perl.
133 164
134=back 165=back
135 166
136 167
168=head1 A FEW NOTES ON UNICODE AND PERL
169
170Since this often leads to confusion, here are a few very clear words on
171how Unicode works in Perl, modulo bugs.
172
173=over 4
174
175=item 1. Perl strings can store characters with ordinal values > 255.
176
177This enables you to store Unicode characters as single characters in a
178Perl 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
183printing the scalar to a file, in which case Perl either interprets your
184string as locale-encoded text, octets/binary, or as Unicode, depending
185on various settings. In no case is an encoding stored together with your
186data, 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
189encoding of your string.
190
191Just ignore that flag unless you debug a Perl bug, a module written in
192XS or want to dive into the internals of perl. Otherwise it will only
193confuse you, as, despite the name, it says nothing about how your string
194is encoded. You can have Unicode strings with that flag set, with that
195flag clear, and you can have binary data with that flag set and that flag
196clear. Other possibilities exist, too.
197
198If you didn't know about that flag, just the better, pretend it doesn't
199exist.
200
201=item 4. A "Unicode String" is simply a string where each character can be
202validly interpreted as a Unicode codepoint.
203
204If you have UTF-8 encoded data, it is no longer a Unicode string, but a
205Unicode 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
209It's a fact. Learn to live with it.
210
211=back
212
213I hope this helps :)
214
215
137=head1 OBJECT-ORIENTED INTERFACE 216=head1 OBJECT-ORIENTED INTERFACE
138 217
139The object oriented interface lets you configure your own encoding or 218The object oriented interface lets you configure your own encoding or
140decoding style, within the limits of supported formats. 219decoding style, within the limits of supported formats.
141 220
152 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]})
153 => {"a": [1, 2]} 232 => {"a": [1, 2]}
154 233
155=item $json = $json->ascii ([$enable]) 234=item $json = $json->ascii ([$enable])
156 235
236=item $enabled = $json->get_ascii
237
157If C<$enable> is true (or missing), then the C<encode> method will not 238If C<$enable> is true (or missing), then the C<encode> method will not
158generate characters outside the code range C<0..127> (which is ASCII). Any 239generate characters outside the code range C<0..127> (which is ASCII). Any
159unicode characters outside that range will be escaped using either a 240Unicode characters outside that range will be escaped using either a
160single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, 241single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
161as per RFC4627. The resulting encoded JSON text can be treated as a native 242as per RFC4627. The resulting encoded JSON text can be treated as a native
162unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string, 243Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
163or any other superset of ASCII. 244or any other superset of ASCII.
164 245
165If C<$enable> is false, then the C<encode> method will not escape Unicode 246If C<$enable> is false, then the C<encode> method will not escape Unicode
166characters unless required by the JSON syntax or other flags. This results 247characters unless required by the JSON syntax or other flags. This results
167in a faster and more compact format. 248in a faster and more compact format.
168 249
250See also the section I<ENCODING/CODESET FLAG NOTES> later in this
251document.
252
169The main use for this flag is to produce JSON texts that can be 253The main use for this flag is to produce JSON texts that can be
170transmitted over a 7-bit channel, as the encoded JSON texts will not 254transmitted over a 7-bit channel, as the encoded JSON texts will not
171contain any 8 bit characters. 255contain any 8 bit characters.
172 256
173 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 257 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
174 => ["\ud801\udc01"] 258 => ["\ud801\udc01"]
175 259
176=item $json = $json->latin1 ([$enable]) 260=item $json = $json->latin1 ([$enable])
177 261
262=item $enabled = $json->get_latin1
263
178If C<$enable> is true (or missing), then the C<encode> method will encode 264If C<$enable> is true (or missing), then the C<encode> method will encode
179the resulting JSON text as latin1 (or iso-8859-1), escaping any characters 265the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
180outside the code range C<0..255>. The resulting string can be treated as a 266outside the code range C<0..255>. The resulting string can be treated as a
181latin1-encoded JSON text or a native unicode string. The C<decode> method 267latin1-encoded JSON text or a native Unicode string. The C<decode> method
182will not be affected in any way by this flag, as C<decode> by default 268will not be affected in any way by this flag, as C<decode> by default
183expects unicode, which is a strict superset of latin1. 269expects Unicode, which is a strict superset of latin1.
184 270
185If C<$enable> is false, then the C<encode> method will not escape Unicode 271If C<$enable> is false, then the C<encode> method will not escape Unicode
186characters unless required by the JSON syntax or other flags. 272characters unless required by the JSON syntax or other flags.
273
274See also the section I<ENCODING/CODESET FLAG NOTES> later in this
275document.
187 276
188The main use for this flag is efficiently encoding binary data as JSON 277The main use for this flag is efficiently encoding binary data as JSON
189text, as most octets will not be escaped, resulting in a smaller encoded 278text, as most octets will not be escaped, resulting in a smaller encoded
190size. The disadvantage is that the resulting JSON text is encoded 279size. The disadvantage is that the resulting JSON text is encoded
191in latin1 (and must correctly be treated as such when storing and 280in latin1 (and must correctly be treated as such when storing and
192transfering), a rare encoding for JSON. It is therefore most useful when 281transferring), a rare encoding for JSON. It is therefore most useful when
193you want to store data structures known to contain binary data efficiently 282you want to store data structures known to contain binary data efficiently
194in files or databases, not when talking to other JSON encoders/decoders. 283in files or databases, not when talking to other JSON encoders/decoders.
195 284
196 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] 285 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
197 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) 286 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
198 287
199=item $json = $json->utf8 ([$enable]) 288=item $json = $json->utf8 ([$enable])
289
290=item $enabled = $json->get_utf8
200 291
201If C<$enable> is true (or missing), then the C<encode> method will encode 292If C<$enable> is true (or missing), then the C<encode> method will encode
202the JSON result into UTF-8, as required by many protocols, while the 293the JSON result into UTF-8, as required by many protocols, while the
203C<decode> method expects to be handled an UTF-8-encoded string. Please 294C<decode> method expects to be handled an UTF-8-encoded string. Please
204note that UTF-8-encoded strings do not contain any characters outside the 295note that UTF-8-encoded strings do not contain any characters outside the
205range C<0..255>, they are thus useful for bytewise/binary I/O. In future 296range C<0..255>, they are thus useful for bytewise/binary I/O. In future
206versions, enabling this option might enable autodetection of the UTF-16 297versions, enabling this option might enable autodetection of the UTF-16
207and UTF-32 encoding families, as described in RFC4627. 298and UTF-32 encoding families, as described in RFC4627.
208 299
209If C<$enable> is false, then the C<encode> method will return the JSON 300If C<$enable> is false, then the C<encode> method will return the JSON
210string as a (non-encoded) unicode string, while C<decode> expects thus a 301string as a (non-encoded) Unicode string, while C<decode> expects thus a
211unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs 302Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
212to be done yourself, e.g. using the Encode module. 303to be done yourself, e.g. using the Encode module.
304
305See also the section I<ENCODING/CODESET FLAG NOTES> later in this
306document.
213 307
214Example, output UTF-16BE-encoded JSON: 308Example, output UTF-16BE-encoded JSON:
215 309
216 use Encode; 310 use Encode;
217 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); 311 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
238 ] 332 ]
239 } 333 }
240 334
241=item $json = $json->indent ([$enable]) 335=item $json = $json->indent ([$enable])
242 336
337=item $enabled = $json->get_indent
338
243If C<$enable> is true (or missing), then the C<encode> method will use a multiline 339If C<$enable> is true (or missing), then the C<encode> method will use a multiline
244format as output, putting every array member or object/hash key-value pair 340format as output, putting every array member or object/hash key-value pair
245into its own line, identing them properly. 341into its own line, indenting them properly.
246 342
247If C<$enable> is false, no newlines or indenting will be produced, and the 343If C<$enable> is false, no newlines or indenting will be produced, and the
248resulting JSON text is guarenteed not to contain any C<newlines>. 344resulting JSON text is guaranteed not to contain any C<newlines>.
249 345
250This setting has no effect when decoding JSON texts. 346This setting has no effect when decoding JSON texts.
251 347
252=item $json = $json->space_before ([$enable]) 348=item $json = $json->space_before ([$enable])
349
350=item $enabled = $json->get_space_before
253 351
254If C<$enable> is true (or missing), then the C<encode> method will add an extra 352If C<$enable> is true (or missing), then the C<encode> method will add an extra
255optional space before the C<:> separating keys from values in JSON objects. 353optional space before the C<:> separating keys from values in JSON objects.
256 354
257If C<$enable> is false, then the C<encode> method will not add any extra 355If C<$enable> is false, then the C<encode> method will not add any extra
263Example, space_before enabled, space_after and indent disabled: 361Example, space_before enabled, space_after and indent disabled:
264 362
265 {"key" :"value"} 363 {"key" :"value"}
266 364
267=item $json = $json->space_after ([$enable]) 365=item $json = $json->space_after ([$enable])
366
367=item $enabled = $json->get_space_after
268 368
269If C<$enable> is true (or missing), then the C<encode> method will add an extra 369If C<$enable> is true (or missing), then the C<encode> method will add an extra
270optional space after the C<:> separating keys from values in JSON objects 370optional space after the C<:> separating keys from values in JSON objects
271and extra whitespace after the C<,> separating key-value pairs and array 371and extra whitespace after the C<,> separating key-value pairs and array
272members. 372members.
278 378
279Example, space_before and indent disabled, space_after enabled: 379Example, space_before and indent disabled, space_after enabled:
280 380
281 {"key": "value"} 381 {"key": "value"}
282 382
383=item $json = $json->relaxed ([$enable])
384
385=item $enabled = $json->get_relaxed
386
387If C<$enable> is true (or missing), then C<decode> will accept some
388extensions to normal JSON syntax (see below). C<encode> will not be
389affected in anyway. I<Be aware that this option makes you accept invalid
390JSON texts as if they were valid!>. I suggest only to use this option to
391parse application-specific files written by humans (configuration files,
392resource files etc.)
393
394If C<$enable> is false (the default), then C<decode> will only accept
395valid JSON texts.
396
397Currently accepted extensions are:
398
399=over 4
400
401=item * list items can have an end-comma
402
403JSON I<separates> array elements and key-value pairs with commas. This
404can be annoying if you write JSON texts manually and want to be able to
405quickly append elements, so this extension accepts comma at the end of
406such 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
419Whenever JSON allows whitespace, shell-style comments are additionally
420allowed. They are terminated by the first carriage-return or line-feed
421character, 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
283=item $json = $json->canonical ([$enable]) 430=item $json = $json->canonical ([$enable])
431
432=item $enabled = $json->get_canonical
284 433
285If C<$enable> is true (or missing), then the C<encode> method will output JSON objects 434If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
286by sorting their keys. This is adding a comparatively high overhead. 435by sorting their keys. This is adding a comparatively high overhead.
287 436
288If C<$enable> is false, then the C<encode> method will output key-value 437If C<$enable> is false, then the C<encode> method will output key-value
289pairs in the order Perl stores them (which will likely change between runs 438pairs in the order Perl stores them (which will likely change between runs
290of the same script). 439of the same script).
291 440
292This option is useful if you want the same data structure to be encoded as 441This option is useful if you want the same data structure to be encoded as
293the same JSON text (given the same overall settings). If it is disabled, 442the same JSON text (given the same overall settings). If it is disabled,
294the same hash migh be encoded differently even if contains the same data, 443the same hash might be encoded differently even if contains the same data,
295as key-value pairs have no inherent ordering in Perl. 444as key-value pairs have no inherent ordering in Perl.
296 445
297This setting has no effect when decoding JSON texts. 446This setting has no effect when decoding JSON texts.
298 447
299=item $json = $json->allow_nonref ([$enable]) 448=item $json = $json->allow_nonref ([$enable])
449
450=item $enabled = $json->get_allow_nonref
300 451
301If C<$enable> is true (or missing), then the C<encode> method can convert a 452If C<$enable> is true (or missing), then the C<encode> method can convert a
302non-reference into its corresponding string, number or null JSON value, 453non-reference into its corresponding string, number or null JSON value,
303which is an extension to RFC4627. Likewise, C<decode> will accept those JSON 454which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
304values instead of croaking. 455values instead of croaking.
312resulting in an invalid JSON text: 463resulting in an invalid JSON text:
313 464
314 JSON::XS->new->allow_nonref->encode ("Hello, World!") 465 JSON::XS->new->allow_nonref->encode ("Hello, World!")
315 => "Hello, World!" 466 => "Hello, World!"
316 467
468=item $json = $json->allow_unknown ([$enable])
469
470=item $enabled = $json->get_allow_unknown
471
472If C<$enable> is true (or missing), then C<encode> will I<not> throw an
473exception when it encounters values it cannot represent in JSON (for
474example, filehandles) but instead will encode a JSON C<null> value. Note
475that blessed objects are not included here and are handled separately by
476c<allow_nonref>.
477
478If C<$enable> is false (the default), then C<encode> will throw an
479exception when it encounters anything it cannot encode as JSON.
480
481This option does not affect C<decode> in any way, and it is recommended to
482leave it off unless you know your communications partner.
483
317=item $json = $json->allow_blessed ([$enable]) 484=item $json = $json->allow_blessed ([$enable])
485
486=item $enabled = $json->get_allow_blessed
318 487
319If C<$enable> is true (or missing), then the C<encode> method will not 488If C<$enable> is true (or missing), then the C<encode> method will not
320barf when it encounters a blessed reference. Instead, the value of the 489barf when it encounters a blessed reference. Instead, the value of the
321B<convert_blessed> option will decide wether C<null> (C<convert_blessed> 490B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
322disabled or no C<to_json> method found) or a representation of the 491disabled or no C<TO_JSON> method found) or a representation of the
323object (C<convert_blessed> enabled and C<to_json> method found) is being 492object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
324encoded. Has no effect on C<decode>. 493encoded. Has no effect on C<decode>.
325 494
326If C<$enable> is false (the default), then C<encode> will throw an 495If C<$enable> is false (the default), then C<encode> will throw an
327exception when it encounters a blessed object. 496exception when it encounters a blessed object.
328 497
329=item $json = $json->convert_blessed ([$enable]) 498=item $json = $json->convert_blessed ([$enable])
499
500=item $enabled = $json->get_convert_blessed
330 501
331If C<$enable> is true (or missing), then C<encode>, upon encountering a 502If C<$enable> is true (or missing), then C<encode>, upon encountering a
332blessed object, will check for the availability of the C<TO_JSON> method 503blessed object, will check for the availability of the C<TO_JSON> method
333on the object's class. If found, it will be called in scalar context 504on the object's class. If found, it will be called in scalar context
334and the resulting scalar will be encoded instead of the object. If no 505and the resulting scalar will be encoded instead of the object. If no
338The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON> 509The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
339returns other blessed objects, those will be handled in the same 510returns other blessed objects, those will be handled in the same
340way. C<TO_JSON> must take care of not causing an endless recursion cycle 511way. C<TO_JSON> must take care of not causing an endless recursion cycle
341(== crash) in this case. The name of C<TO_JSON> was chosen because other 512(== crash) in this case. The name of C<TO_JSON> was chosen because other
342methods called by the Perl core (== not by the user of the object) are 513methods called by the Perl core (== not by the user of the object) are
343usually in upper case letters and to avoid collisions with the C<to_json> 514usually in upper case letters and to avoid collisions with any C<to_json>
344function. 515function or method.
345 516
346This setting does not yet influence C<decode> in any way, but in the 517This setting does not yet influence C<decode> in any way, but in the
347future, global hooks might get installed that influence C<decode> and are 518future, global hooks might get installed that influence C<decode> and are
348enabled by this setting. 519enabled by this setting.
349 520
350If C<$enable> is false, then the C<allow_blessed> setting will decide what 521If C<$enable> is false, then the C<allow_blessed> setting will decide what
351to do when a blessed object is found. 522to do when a blessed object is found.
352 523
353=item $json = $json->filter_json_object ([$coderef]) 524=item $json = $json->filter_json_object ([$coderef->($hashref)])
354 525
355When C<$coderef> is specified, it will be called from C<decode> each 526When C<$coderef> is specified, it will be called from C<decode> each
356time it decodes a JSON object. The only argument is a reference to the 527time it decodes a JSON object. The only argument is a reference to the
357newly-created hash. If the code references returns a single scalar (which 528newly-created hash. If the code references returns a single scalar (which
358need not be a reference), this value (i.e. a copy of that scalar to avoid 529need not be a reference), this value (i.e. a copy of that scalar to avoid
359aliasing) is inserted into the deserialised data structure. If it returns 530aliasing) is inserted into the deserialised data structure. If it returns
360an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the 531an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
361original deserialised hash will be inserted. This setting can slow down 532original deserialised hash will be inserted. This setting can slow down
362decoding considerably. 533decoding considerably.
363 534
364When C<$coderef> is omitted or undefined, C<decode> will not change the 535When C<$coderef> is omitted or undefined, any existing callback will
365deserialised hash in any way. This is maximally fast. 536be removed and C<decode> will not change the deserialised hash in any
537way.
366 538
367Example, convert all JSON objects into the integer 5: 539Example, convert all JSON objects into the integer 5:
368 540
369 my $js = JSON::XS->new->filter_json_object (sub { 5 }); 541 my $js = JSON::XS->new->filter_json_object (sub { 5 });
370 # returns [5] 542 # returns [5]
371 $js->decode ('[{}]') 543 $js->decode ('[{}]')
372 # throw an exception because allow_nonref is not enabled: 544 # throw an exception because allow_nonref is not enabled
545 # so a lone 5 is not allowed.
373 $js->decode ('{"a":1, "b":2}'); 546 $js->decode ('{"a":1, "b":2}');
374 547
375=item $json = $json->filter_json_single_key_object ([$coderef]) 548=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
376 549
377Works like C<filter_json_object>, but is only called for JSON objects 550Works remotely similar to C<filter_json_object>, but is only called for
378having only a single key. 551JSON objects having a single key named C<$key>.
379 552
380This C<$coderef> is called before the one specified via 553This C<$coderef> is called before the one specified via
381C<filter_json_object>, if any. If it returns something, that will be 554C<filter_json_object>, if any. It gets passed the single value in the JSON
382inserted into the data structure. If it returns nothing, the callback 555object. If it returns a single value, it will be inserted into the data
383from C<filter_json_object> will be called next. If you want to force 556structure. If it returns nothing (not even C<undef> but the empty list),
384insertion of single-key objects even in the presence of a mutating 557the callback from C<filter_json_object> will be called next, as if no
385C<filter_json_object> callback, simply return the passed hash. 558single-key callback were specified.
559
560If C<$coderef> is omitted or undefined, the corresponding callback will be
561disabled. There can only ever be one callback for a given key.
386 562
387As this callback gets called less often then the C<filter_json_object> 563As this callback gets called less often then the C<filter_json_object>
388one, decoding speed will not usually suffer as much. Therefore, single-key 564one, decoding speed will not usually suffer as much. Therefore, single-key
389objects make excellent targets to serialise Perl objects into, especially 565objects make excellent targets to serialise Perl objects into, especially
390as single-key JSON objects are as close to the type-tagged value concept 566as single-key JSON objects are as close to the type-tagged value concept
391as JSON gets (its basically an ID/VALUE tuple). Of course, JSON does not 567as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
392support this in any way, so you need to make sure your data never looks 568support this in any way, so you need to make sure your data never looks
393like a serialised Perl hash. 569like a serialised Perl hash.
394 570
395Typical names for the single object key are C<__class_whatever__>, or 571Typical names for the single object key are C<__class_whatever__>, or
396C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even 572C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
401into the corresponding C<< $WIDGET{<id>} >> object: 577into the corresponding C<< $WIDGET{<id>} >> object:
402 578
403 # return whatever is in $WIDGET{5}: 579 # return whatever is in $WIDGET{5}:
404 JSON::XS 580 JSON::XS
405 ->new 581 ->new
406 ->filter_json_single_key_object (sub { 582 ->filter_json_single_key_object (__widget__ => sub {
407 exists $_[0]{__widget__}
408 ? $WIDGET{ $_[0]{__widget__} } 583 $WIDGET{ $_[0] }
409 : ()
410 }) 584 })
411 ->decode ('{"__widget__": 5') 585 ->decode ('{"__widget__": 5')
412 586
413 # this can be used with a TO_JSON method in some "widget" class 587 # this can be used with a TO_JSON method in some "widget" class
414 # for serialisation to json: 588 # for serialisation to json:
422 596
423 { __widget__ => $self->{id} } 597 { __widget__ => $self->{id} }
424 } 598 }
425 599
426=item $json = $json->shrink ([$enable]) 600=item $json = $json->shrink ([$enable])
601
602=item $enabled = $json->get_shrink
427 603
428Perl usually over-allocates memory a bit when allocating space for 604Perl usually over-allocates memory a bit when allocating space for
429strings. This flag optionally resizes strings generated by either 605strings. This flag optionally resizes strings generated by either
430C<encode> or C<decode> to their minimum size possible. This can save 606C<encode> or C<decode> to their minimum size possible. This can save
431memory when your JSON texts are either very very long or you have many 607memory when your JSON texts are either very very long or you have many
449strings that look like integers or floats into integers or floats 625strings that look like integers or floats into integers or floats
450internally (there is no difference on the Perl level), saving space. 626internally (there is no difference on the Perl level), saving space.
451 627
452=item $json = $json->max_depth ([$maximum_nesting_depth]) 628=item $json = $json->max_depth ([$maximum_nesting_depth])
453 629
630=item $max_depth = $json->get_max_depth
631
454Sets the maximum nesting level (default C<512>) accepted while encoding 632Sets the maximum nesting level (default C<512>) accepted while encoding
455or decoding. If the JSON text or Perl data structure has an equal or 633or decoding. If a higher nesting level is detected in JSON text or a Perl
456higher nesting level then this limit, then the encoder and decoder will 634data structure, then the encoder and decoder will stop and croak at that
457stop and croak at that point. 635point.
458 636
459Nesting level is defined by number of hash- or arrayrefs that the encoder 637Nesting level is defined by number of hash- or arrayrefs that the encoder
460needs to traverse to reach a given point or the number of C<{> or C<[> 638needs to traverse to reach a given point or the number of C<{> or C<[>
461characters without their matching closing parenthesis crossed to reach a 639characters without their matching closing parenthesis crossed to reach a
462given character in a string. 640given character in a string.
463 641
464Setting the maximum depth to one disallows any nesting, so that ensures 642Setting the maximum depth to one disallows any nesting, so that ensures
465that the object is only a single hash/object or array. 643that the object is only a single hash/object or array.
466 644
467The argument to C<max_depth> will be rounded up to the next highest power
468of two. If no argument is given, the highest possible setting will be 645If no argument is given, the highest possible setting will be used, which
469used, which is rarely useful. 646is rarely useful.
647
648Note that nesting is implemented by recursion in C. The default value has
649been chosen to be as large as typical operating systems allow without
650crashing.
470 651
471See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 652See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
472 653
473=item $json = $json->max_size ([$maximum_string_size]) 654=item $json = $json->max_size ([$maximum_string_size])
655
656=item $max_size = $json->get_max_size
474 657
475Set the maximum length a JSON text may have (in bytes) where decoding is 658Set the maximum length a JSON text may have (in bytes) where decoding is
476being attempted. The default is C<0>, meaning no limit. When C<decode> 659being attempted. The default is C<0>, meaning no limit. When C<decode>
477is called on a string longer then this number of characters it will not 660is called on a string that is longer then this many bytes, it will not
478attempt to decode the string but throw an exception. This setting has no 661attempt to decode the string but throw an exception. This setting has no
479effect on C<encode> (yet). 662effect on C<encode> (yet).
480 663
481The argument to C<max_size> will be rounded up to the next B<highest> 664If no argument is given, the limit check will be deactivated (same as when
482power of two (so may be more than requested). If no argument is given, the 665C<0> is specified).
483limit check will be deactivated (same as when C<0> is specified).
484 666
485See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 667See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
486 668
487=item $json_text = $json->encode ($perl_scalar) 669=item $json_text = $json->encode ($perl_scalar)
488 670
517 => ([], 3) 699 => ([], 3)
518 700
519=back 701=back
520 702
521 703
704=head1 INCREMENTAL PARSING
705
706[This section and the API it details is still EXPERIMENTAL]
707
708In some cases, there is the need for incremental parsing of JSON
709texts. While this module always has to keep both JSON text and resulting
710Perl data structure in memory at one time, it does allow you to parse a
711JSON stream incrementally. It does so by accumulating text until it has
712a full JSON object, which it then can decode. This process is similar to
713using C<decode_prefix> to see if a full JSON object is available, but is
714much more efficient (JSON::XS will only attempt to parse the JSON text
715once it is sure it has enough text to get a decisive result, using a very
716simple but truly incremental parser).
717
718The following two methods deal with this.
719
720=over 4
721
722=item [void, scalar or list context] = $json->incr_parse ([$string])
723
724This is the central parsing function. It can both append new text and
725extract objects from the stream accumulated so far (both of these
726functions are optional).
727
728If C<$string> is given, then this string is appended to the already
729existing JSON fragment stored in the C<$json> object.
730
731After that, if the function is called in void context, it will simply
732return without doing anything further. This can be used to add more text
733in as many chunks as you want.
734
735If the method is called in scalar context, then it will try to extract
736exactly I<one> JSON object. If that is successful, it will return this
737object, otherwise it will return C<undef>. If there is a parse error,
738this method will croak just as C<decode> would do (one can then use
739C<incr_skip> to skip the errornous part). This is the most common way of
740using the method.
741
742And finally, in list context, it will try to extract as many objects
743from the stream as it can find and return them, or the empty list
744otherwise. For this to work, there must be no separators between the JSON
745objects or arrays, instead they must be concatenated back-to-back. If
746an error occurs, an exception will be raised as in the scalar context
747case. Note that in this case, any previously-parsed JSON texts will be
748lost.
749
750=item $lvalue_string = $json->incr_text
751
752This method returns the currently stored JSON fragment as an lvalue, that
753is, you can manipulate it. This I<only> works when a preceding call to
754C<incr_parse> in I<scalar context> successfully returned an object. Under
755all other circumstances you must not call this function (I mean it.
756although in simple tests it might actually work, it I<will> fail under
757real world conditions). As a special exception, you can also call this
758method before having parsed anything.
759
760This function is useful in two cases: a) finding the trailing text after a
761JSON object or b) parsing multiple JSON objects separated by non-JSON text
762(such as commas).
763
764=item $json->incr_skip
765
766This will reset the state of the incremental parser and will remove the
767parsed text from the input buffer. This is useful after C<incr_parse>
768died, in which case the input buffer and incremental parser state is left
769unchanged, to skip the text parsed so far and to reset the parse state.
770
771=back
772
773=head2 LIMITATIONS
774
775All options that affect decoding are supported, except
776C<allow_nonref>. The reason for this is that it cannot be made to
777work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
778them back to back and still decode them perfectly. This does not hold true
779for JSON numbers, however.
780
781For example, is the string C<1> a single JSON number, or is it simply the
782start of C<12>? Or is C<12> a single JSON number, or the concatenation
783of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
784takes the conservative route and disallows this case.
785
786=head2 EXAMPLES
787
788Some examples will make all this clearer. First, a simple example that
789works similarly to C<decode_prefix>: We want to decode the JSON object at
790the start of a string and identify the portion after the JSON object:
791
792 my $text = "[1,2,3] hello";
793
794 my $json = new JSON::XS;
795
796 my $obj = $json->incr_parse ($text)
797 or die "expected JSON object or array at beginning of string";
798
799 my $tail = $json->incr_text;
800 # $tail now contains " hello"
801
802Easy, isn't it?
803
804Now for a more complicated example: Imagine a hypothetical protocol where
805you read some requests from a TCP stream, and each request is a JSON
806array, without any separation between them (in fact, it is often useful to
807use newlines as "separators", as these get interpreted as whitespace at
808the start of the JSON text, which makes it possible to test said protocol
809with C<telnet>...).
810
811Here is how you'd do it (it is trivial to write this in an event-based
812manner):
813
814 my $json = new JSON::XS;
815
816 # read some data from the socket
817 while (sysread $socket, my $buf, 4096) {
818
819 # split and decode as many requests as possible
820 for my $request ($json->incr_parse ($buf)) {
821 # act on the $request
822 }
823 }
824
825Another complicated example: Assume you have a string with JSON objects
826or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
827[3]>). To parse them, we have to skip the commas between the JSON texts,
828and here is where the lvalue-ness of C<incr_text> comes in useful:
829
830 my $text = "[1],[2], [3]";
831 my $json = new JSON::XS;
832
833 # void context, so no parsing done
834 $json->incr_parse ($text);
835
836 # now extract as many objects as possible. note the
837 # use of scalar context so incr_text can be called.
838 while (my $obj = $json->incr_parse) {
839 # do something with $obj
840
841 # now skip the optional comma
842 $json->incr_text =~ s/^ \s* , //x;
843 }
844
845Now lets go for a very complex example: Assume that you have a gigantic
846JSON array-of-objects, many gigabytes in size, and you want to parse it,
847but you cannot load it into memory fully (this has actually happened in
848the real world :).
849
850Well, you lost, you have to implement your own JSON parser. But JSON::XS
851can still help you: You implement a (very simple) array parser and let
852JSON decode the array elements, which are all full JSON objects on their
853own (this wouldn't work if the array elements could be JSON numbers, for
854example):
855
856 my $json = new JSON::XS;
857
858 # open the monster
859 open my $fh, "<bigfile.json"
860 or die "bigfile: $!";
861
862 # first parse the initial "["
863 for (;;) {
864 sysread $fh, my $buf, 65536
865 or die "read error: $!";
866 $json->incr_parse ($buf); # void context, so no parsing
867
868 # Exit the loop once we found and removed(!) the initial "[".
869 # In essence, we are (ab-)using the $json object as a simple scalar
870 # we append data to.
871 last if $json->incr_text =~ s/^ \s* \[ //x;
872 }
873
874 # now we have the skipped the initial "[", so continue
875 # parsing all the elements.
876 for (;;) {
877 # in this loop we read data until we got a single JSON object
878 for (;;) {
879 if (my $obj = $json->incr_parse) {
880 # do something with $obj
881 last;
882 }
883
884 # add more data
885 sysread $fh, my $buf, 65536
886 or die "read error: $!";
887 $json->incr_parse ($buf); # void context, so no parsing
888 }
889
890 # in this loop we read data until we either found and parsed the
891 # separating "," between elements, or the final "]"
892 for (;;) {
893 # first skip whitespace
894 $json->incr_text =~ s/^\s*//;
895
896 # if we find "]", we are done
897 if ($json->incr_text =~ s/^\]//) {
898 print "finished.\n";
899 exit;
900 }
901
902 # if we find ",", we can continue with the next element
903 if ($json->incr_text =~ s/^,//) {
904 last;
905 }
906
907 # if we find anything else, we have a parse error!
908 if (length $json->incr_text) {
909 die "parse error near ", $json->incr_text;
910 }
911
912 # else add more data
913 sysread $fh, my $buf, 65536
914 or die "read error: $!";
915 $json->incr_parse ($buf); # void context, so no parsing
916 }
917
918This is a complex example, but most of the complexity comes from the fact
919that we are trying to be correct (bear with me if I am wrong, I never ran
920the above example :).
921
922
923
522=head1 MAPPING 924=head1 MAPPING
523 925
524This section describes how JSON::XS maps Perl values to JSON values and 926This section describes how JSON::XS maps Perl values to JSON values and
525vice versa. These mappings are designed to "do the right thing" in most 927vice versa. These mappings are designed to "do the right thing" in most
526circumstances automatically, preserving round-tripping characteristics 928circumstances automatically, preserving round-tripping characteristics
527(what you put in comes out as something equivalent). 929(what you put in comes out as something equivalent).
528 930
529For the more enlightened: note that in the following descriptions, 931For the more enlightened: note that in the following descriptions,
530lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl> 932lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
531refers to the abstract Perl language itself. 933refers to the abstract Perl language itself.
532 934
533 935
534=head2 JSON -> PERL 936=head2 JSON -> PERL
535 937
536=over 4 938=over 4
537 939
538=item object 940=item object
539 941
540A JSON object becomes a reference to a hash in Perl. No ordering of object 942A JSON object becomes a reference to a hash in Perl. No ordering of object
541keys is preserved (JSON does not preserver object key ordering itself). 943keys is preserved (JSON does not preserve object key ordering itself).
542 944
543=item array 945=item array
544 946
545A JSON array becomes a reference to an array in Perl. 947A JSON array becomes a reference to an array in Perl.
546 948
550are represented by the same codepoints in the Perl string, so no manual 952are represented by the same codepoints in the Perl string, so no manual
551decoding is necessary. 953decoding is necessary.
552 954
553=item number 955=item number
554 956
555A JSON number becomes either an integer or numeric (floating point) 957A JSON number becomes either an integer, numeric (floating point) or
556scalar in perl, depending on its range and any fractional parts. On the 958string scalar in perl, depending on its range and any fractional parts. On
557Perl level, there is no difference between those as Perl handles all the 959the Perl level, there is no difference between those as Perl handles all
558conversion details, but an integer may take slightly less memory and might 960the conversion details, but an integer may take slightly less memory and
559represent more values exactly than (floating point) numbers. 961might represent more values exactly than floating point numbers.
962
963If the number consists of digits only, JSON::XS will try to represent
964it as an integer value. If that fails, it will try to represent it as
965a numeric (floating point) value if that is possible without loss of
966precision. Otherwise it will preserve the number as a string value (in
967which case you lose roundtripping ability, as the JSON number will be
968re-encoded toa JSON string).
969
970Numbers containing a fractional or exponential part will always be
971represented as numeric (floating point) values, possibly at a loss of
972precision (in which case you might lose perfect roundtripping ability, but
973the JSON number will still be re-encoded as a JSON number).
560 974
561=item true, false 975=item true, false
562 976
563These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, 977These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
564respectively. They are overloaded to act almost exactly like the numbers 978respectively. They are overloaded to act almost exactly like the numbers
565C<1> and C<0>. You can check wether a scalar is a JSON boolean by using 979C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
566the C<JSON::XS::is_bool> function. 980the C<JSON::XS::is_bool> function.
567 981
568=item null 982=item null
569 983
570A JSON null atom becomes C<undef> in Perl. 984A JSON null atom becomes C<undef> in Perl.
601Other unblessed references are generally not allowed and will cause an 1015Other unblessed references are generally not allowed and will cause an
602exception to be thrown, except for references to the integers C<0> and 1016exception to be thrown, except for references to the integers C<0> and
603C<1>, which get turned into C<false> and C<true> atoms in JSON. You can 1017C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
604also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. 1018also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
605 1019
606 to_json [\0,JSON::XS::true] # yields [false,true] 1020 encode_json [\0,JSON::XS::true] # yields [false,true]
607 1021
608=item JSON::XS::true, JSON::XS::false 1022=item JSON::XS::true, JSON::XS::false
609 1023
610These special values become JSON true and JSON false values, 1024These special values become JSON true and JSON false values,
611respectively. You cna alos use C<\1> and C<\0> directly if you want. 1025respectively. You can also use C<\1> and C<\0> directly if you want.
612 1026
613=item blessed objects 1027=item blessed objects
614 1028
615Blessed objects are not allowed. JSON::XS currently tries to encode their 1029Blessed objects are not directly representable in JSON. See the
616underlying representation (hash- or arrayref), but this behaviour might 1030C<allow_blessed> and C<convert_blessed> methods on various options on
617change in future versions. 1031how to deal with this: basically, you can choose between throwing an
1032exception, encoding the reference as if it weren't blessed, or provide
1033your own serialiser method.
618 1034
619=item simple scalars 1035=item simple scalars
620 1036
621Simple Perl scalars (any scalar that is not a reference) are the most 1037Simple Perl scalars (any scalar that is not a reference) are the most
622difficult objects to encode: JSON::XS will encode undefined scalars as 1038difficult objects to encode: JSON::XS will encode undefined scalars as
623JSON null value, scalars that have last been used in a string context 1039JSON C<null> values, scalars that have last been used in a string context
624before encoding as JSON strings and anything else as number value: 1040before encoding as JSON strings, and anything else as number value:
625 1041
626 # dump as number 1042 # dump as number
627 to_json [2] # yields [2] 1043 encode_json [2] # yields [2]
628 to_json [-3.0e17] # yields [-3e+17] 1044 encode_json [-3.0e17] # yields [-3e+17]
629 my $value = 5; to_json [$value] # yields [5] 1045 my $value = 5; encode_json [$value] # yields [5]
630 1046
631 # used as string, so dump as string 1047 # used as string, so dump as string
632 print $value; 1048 print $value;
633 to_json [$value] # yields ["5"] 1049 encode_json [$value] # yields ["5"]
634 1050
635 # undef becomes null 1051 # undef becomes null
636 to_json [undef] # yields [null] 1052 encode_json [undef] # yields [null]
637 1053
638You can force the type to be a string by stringifying it: 1054You can force the type to be a JSON string by stringifying it:
639 1055
640 my $x = 3.1; # some variable containing a number 1056 my $x = 3.1; # some variable containing a number
641 "$x"; # stringified 1057 "$x"; # stringified
642 $x .= ""; # another, more awkward way to stringify 1058 $x .= ""; # another, more awkward way to stringify
643 print $x; # perl does it for you, too, quite often 1059 print $x; # perl does it for you, too, quite often
644 1060
645You can force the type to be a number by numifying it: 1061You can force the type to be a JSON number by numifying it:
646 1062
647 my $x = "3"; # some variable containing a string 1063 my $x = "3"; # some variable containing a string
648 $x += 0; # numify it, ensuring it will be dumped as a number 1064 $x += 0; # numify it, ensuring it will be dumped as a number
649 $x *= 1; # same thing, the choise is yours. 1065 $x *= 1; # same thing, the choice is yours.
650 1066
651You can not currently output JSON booleans or force the type in other, 1067You can not currently force the type in other, less obscure, ways. Tell me
652less obscure, ways. Tell me if you need this capability. 1068if you need this capability (but don't forget to explain why it's needed
1069:).
653 1070
654=back 1071=back
655 1072
656 1073
657=head1 COMPARISON 1074=head1 ENCODING/CODESET FLAG NOTES
658 1075
659As already mentioned, this module was created because none of the existing 1076The interested reader might have seen a number of flags that signify
660JSON modules could be made to work correctly. First I will describe the 1077encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
661problems (or pleasures) I encountered with various existing JSON modules, 1078some confusion on what these do, so here is a short comparison:
662followed by some benchmark values. JSON::XS was designed not to suffer 1079
663from any of these problems or limitations. 1080C<utf8> controls whether the JSON text created by C<encode> (and expected
1081by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
1082control whether C<encode> escapes character values outside their respective
1083codeset range. Neither of these flags conflict with each other, although
1084some combinations make less sense than others.
1085
1086Care has been taken to make all flags symmetrical with respect to
1087C<encode> and C<decode>, that is, texts encoded with any combination of
1088these flag values will be correctly decoded when the same flags are used
1089- in general, if you use different flag settings while encoding vs. when
1090decoding you likely have a bug somewhere.
1091
1092Below comes a verbose discussion of these flags. Note that a "codeset" is
1093simply an abstract set of character-codepoint pairs, while an encoding
1094takes those codepoint numbers and I<encodes> them, in our case into
1095octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
1096and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
1097the same time, which can be confusing.
664 1098
665=over 4 1099=over 4
666 1100
667=item JSON 1.07 1101=item C<utf8> flag disabled
668 1102
669Slow (but very portable, as it is written in pure Perl). 1103When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
1104and expect Unicode strings, that is, characters with high ordinal Unicode
1105values (> 255) will be encoded as such characters, and likewise such
1106characters are decoded as-is, no canges to them will be done, except
1107"(re-)interpreting" them as Unicode codepoints or Unicode characters,
1108respectively (to Perl, these are the same thing in strings unless you do
1109funny/weird/dumb stuff).
670 1110
671Undocumented/buggy Unicode handling (how JSON handles unicode values is 1111This is useful when you want to do the encoding yourself (e.g. when you
672undocumented. One can get far by feeding it unicode strings and doing 1112want to have UTF-16 encoded JSON texts) or when some other layer does
673en-/decoding oneself, but unicode escapes are not working properly). 1113the encoding for you (for example, when printing to a terminal using a
1114filehandle that transparently encodes to UTF-8 you certainly do NOT want
1115to UTF-8 encode your data first and have Perl encode it another time).
674 1116
675No roundtripping (strings get clobbered if they look like numbers, e.g. 1117=item C<utf8> flag enabled
676the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
677decode into the number 2.
678 1118
679=item JSON::PC 0.01 1119If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
1120characters using the corresponding UTF-8 multi-byte sequence, and will
1121expect your input strings to be encoded as UTF-8, that is, no "character"
1122of the input string must have any value > 255, as UTF-8 does not allow
1123that.
680 1124
681Very fast. 1125The C<utf8> flag therefore switches between two modes: disabled means you
1126will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
1127octet/binary string in Perl.
682 1128
683Undocumented/buggy Unicode handling. 1129=item C<latin1> or C<ascii> flags enabled
684 1130
685No roundtripping. 1131With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
1132with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
1133characters as specified by the C<utf8> flag.
686 1134
687Has problems handling many Perl values (e.g. regex results and other magic 1135If C<utf8> is disabled, then the result is also correctly encoded in those
688values will make it croak). 1136character sets (as both are proper subsets of Unicode, meaning that a
1137Unicode string with all character values < 256 is the same thing as a
1138ISO-8859-1 string, and a Unicode string with all character values < 128 is
1139the same thing as an ASCII string in Perl).
689 1140
690Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> 1141If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
691which is not a valid JSON text. 1142regardless of these flags, just some more characters will be escaped using
1143C<\uXXXX> then before.
692 1144
693Unmaintained (maintainer unresponsive for many months, bugs are not 1145Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
694getting fixed). 1146encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
1147encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
1148a subset of Unicode), while ASCII is.
695 1149
696=item JSON::Syck 0.21 1150Surprisingly, C<decode> will ignore these flags and so treat all input
1151values as governed by the C<utf8> flag. If it is disabled, this allows you
1152to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
1153Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
697 1154
698Very buggy (often crashes). 1155So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
1156they only govern when the JSON output engine escapes a character or not.
699 1157
700Very inflexible (no human-readable format supported, format pretty much 1158The main use for C<latin1> is to relatively efficiently store binary data
701undocumented. I need at least a format for easy reading by humans and a 1159as JSON, at the expense of breaking compatibility with most JSON decoders.
702single-line compact format for use in a protocol, and preferably a way to
703generate ASCII-only JSON texts).
704 1160
705Completely broken (and confusingly documented) Unicode handling (unicode 1161The main use for C<ascii> is to force the output to not contain characters
706escapes are not working properly, you need to set ImplicitUnicode to 1162with values > 127, which means you can interpret the resulting string
707I<different> values on en- and decoding to get symmetric behaviour). 1163as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
708 11648-bit-encoding, and still get the same data structure back. This is useful
709No roundtripping (simple cases work, but this depends on wether the scalar 1165when your channel for JSON transfer is not 8-bit clean or the encoding
710value was used in a numeric context or not). 1166might be mangled in between (e.g. in mail), and works because ASCII is a
711 1167proper subset of most 8-bit and multibyte encodings in use in the world.
712Dumping hashes may skip hash values depending on iterator state.
713
714Unmaintained (maintainer unresponsive for many months, bugs are not
715getting fixed).
716
717Does not check input for validity (i.e. will accept non-JSON input and
718return "something" instead of raising an exception. This is a security
719issue: imagine two banks transfering money between each other using
720JSON. One bank might parse a given non-JSON request and deduct money,
721while the other might reject the transaction with a syntax error. While a
722good protocol will at least recover, that is extra unnecessary work and
723the transaction will still not succeed).
724
725=item JSON::DWIW 0.04
726
727Very fast. Very natural. Very nice.
728
729Undocumented unicode handling (but the best of the pack. Unicode escapes
730still don't get parsed properly).
731
732Very inflexible.
733
734No roundtripping.
735
736Does not generate valid JSON texts (key strings are often unquoted, empty keys
737result in nothing being output)
738
739Does not check input for validity.
740 1168
741=back 1169=back
742 1170
743 1171
744=head2 JSON and YAML 1172=head2 JSON and YAML
745 1173
746You often hear that JSON is a subset (or a close subset) of YAML. This is, 1174You often hear that JSON is a subset of YAML. This is, however, a mass
747however, a mass hysteria and very far from the truth. In general, there is 1175hysteria(*) and very far from the truth (as of the time of this writing),
748no way to configure JSON::XS to output a data structure as valid YAML. 1176so let me state it clearly: I<in general, there is no way to configure
1177JSON::XS to output a data structure as valid YAML> that works in all
1178cases.
749 1179
750If you really must use JSON::XS to generate YAML, you should use this 1180If you really must use JSON::XS to generate YAML, you should use this
751algorithm (subject to change in future versions): 1181algorithm (subject to change in future versions):
752 1182
753 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1183 my $to_yaml = JSON::XS->new->utf8->space_after (1);
754 my $yaml = $to_yaml->encode ($ref) . "\n"; 1184 my $yaml = $to_yaml->encode ($ref) . "\n";
755 1185
756This will usually generate JSON texts that also parse as valid 1186This will I<usually> generate JSON texts that also parse as valid
757YAML. Please note that YAML has hardcoded limits on (simple) object key 1187YAML. Please note that YAML has hardcoded limits on (simple) object key
758lengths that JSON doesn't have, so you should make sure that your hash 1188lengths that JSON doesn't have and also has different and incompatible
1189unicode handling, so you should make sure that your hash keys are
759keys are noticably shorter than the 1024 characters YAML allows. 1190noticeably shorter than the 1024 "stream characters" YAML allows and that
1191you do not have characters with codepoint values outside the Unicode BMP
1192(basic multilingual page). YAML also does not allow C<\/> sequences in
1193strings (which JSON::XS does not I<currently> generate, but other JSON
1194generators might).
760 1195
761There might be other incompatibilities that I am not aware of. In general 1196There might be other incompatibilities that I am not aware of (or the YAML
1197specification has been changed yet again - it does so quite often). In
762you should not try to generate YAML with a JSON generator or vice versa, 1198general you should not try to generate YAML with a JSON generator or vice
763or try to parse JSON with a YAML parser or vice versa: chances are high 1199versa, or try to parse JSON with a YAML parser or vice versa: chances are
764that you will run into severe interoperability problems. 1200high that you will run into severe interoperability problems when you
1201least expect it.
1202
1203=over 4
1204
1205=item (*)
1206
1207I have been pressured multiple times by Brian Ingerson (one of the
1208authors of the YAML specification) to remove this paragraph, despite him
1209acknowledging that the actual incompatibilities exist. As I was personally
1210bitten by this "JSON is YAML" lie, I refused and said I will continue to
1211educate people about these issues, so others do not run into the same
1212problem again and again. After this, Brian called me a (quote)I<complete
1213and worthless idiot>(unquote).
1214
1215In my opinion, instead of pressuring and insulting people who actually
1216clarify issues with YAML and the wrong statements of some of its
1217proponents, I would kindly suggest reading the JSON spec (which is not
1218that difficult or long) and finally make YAML compatible to it, and
1219educating users about the changes, instead of spreading lies about the
1220real compatibility for many I<years> and trying to silence people who
1221point out that it isn't true.
1222
1223=back
765 1224
766 1225
767=head2 SPEED 1226=head2 SPEED
768 1227
769It seems that JSON::XS is surprisingly fast, as shown in the following 1228It seems that JSON::XS is surprisingly fast, as shown in the following
770tables. They have been generated with the help of the C<eg/bench> program 1229tables. They have been generated with the help of the C<eg/bench> program
771in the JSON::XS distribution, to make it easy to compare on your own 1230in the JSON::XS distribution, to make it easy to compare on your own
772system. 1231system.
773 1232
774First comes a comparison between various modules using a very short 1233First comes a comparison between various modules using
775single-line JSON string: 1234a very short single-line JSON string (also available at
1235L<http://dist.schmorp.de/misc/json/short.json>).
776 1236
777 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1237 {"method": "handleMessage", "params": ["user1",
778 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1238 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1239 true, false]}
779 1240
780It shows the number of encodes/decodes per second (JSON::XS uses 1241It shows the number of encodes/decodes per second (JSON::XS uses
781the functional interface, while JSON::XS/2 uses the OO interface 1242the functional interface, while JSON::XS/2 uses the OO interface
782with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables 1243with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
783shrink). Higher is better: 1244shrink). Higher is better:
784 1245
785 Storable | 15779.925 | 14169.946 |
786 -----------+------------+------------+
787 module | encode | decode | 1246 module | encode | decode |
788 -----------|------------|------------| 1247 -----------|------------|------------|
789 JSON | 4990.842 | 4088.813 | 1248 JSON 1.x | 4990.842 | 4088.813 |
790 JSON::DWIW | 51653.990 | 71575.154 | 1249 JSON::DWIW | 51653.990 | 71575.154 |
791 JSON::PC | 65948.176 | 74631.744 | 1250 JSON::PC | 65948.176 | 74631.744 |
792 JSON::PP | 8931.652 | 3817.168 | 1251 JSON::PP | 8931.652 | 3817.168 |
793 JSON::Syck | 24877.248 | 27776.848 | 1252 JSON::Syck | 24877.248 | 27776.848 |
794 JSON::XS | 388361.481 | 227951.304 | 1253 JSON::XS | 388361.481 | 227951.304 |
796 JSON::XS/3 | 338250.323 | 218453.333 | 1255 JSON::XS/3 | 338250.323 | 218453.333 |
797 Storable | 16500.016 | 135300.129 | 1256 Storable | 16500.016 | 135300.129 |
798 -----------+------------+------------+ 1257 -----------+------------+------------+
799 1258
800That is, JSON::XS is about five times faster than JSON::DWIW on encoding, 1259That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
801about three times faster on decoding, and over fourty times faster 1260about three times faster on decoding, and over forty times faster
802than JSON, even with pretty-printing and key sorting. It also compares 1261than JSON, even with pretty-printing and key sorting. It also compares
803favourably to Storable for small amounts of data. 1262favourably to Storable for small amounts of data.
804 1263
805Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1264Using a longer test string (roughly 18KB, generated from Yahoo! Locals
806search API (http://nanoref.com/yahooapis/mgPdGg): 1265search API (L<http://dist.schmorp.de/misc/json/long.json>).
807 1266
808 module | encode | decode | 1267 module | encode | decode |
809 -----------|------------|------------| 1268 -----------|------------|------------|
810 JSON | 55.260 | 34.971 | 1269 JSON 1.x | 55.260 | 34.971 |
811 JSON::DWIW | 825.228 | 1082.513 | 1270 JSON::DWIW | 825.228 | 1082.513 |
812 JSON::PC | 3571.444 | 2394.829 | 1271 JSON::PC | 3571.444 | 2394.829 |
813 JSON::PP | 210.987 | 32.574 | 1272 JSON::PP | 210.987 | 32.574 |
814 JSON::Syck | 552.551 | 787.544 | 1273 JSON::Syck | 552.551 | 787.544 |
815 JSON::XS | 5780.463 | 4854.519 | 1274 JSON::XS | 5780.463 | 4854.519 |
819 -----------+------------+------------+ 1278 -----------+------------+------------+
820 1279
821Again, JSON::XS leads by far (except for Storable which non-surprisingly 1280Again, JSON::XS leads by far (except for Storable which non-surprisingly
822decodes faster). 1281decodes faster).
823 1282
824On large strings containing lots of high unicode characters, some modules 1283On large strings containing lots of high Unicode characters, some modules
825(such as JSON::PC) seem to decode faster than JSON::XS, but the result 1284(such as JSON::PC) seem to decode faster than JSON::XS, but the result
826will be broken due to missing (or wrong) unicode handling. Others refuse 1285will be broken due to missing (or wrong) Unicode handling. Others refuse
827to decode or encode properly, so it was impossible to prepare a fair 1286to decode or encode properly, so it was impossible to prepare a fair
828comparison table for that case. 1287comparison table for that case.
829 1288
830 1289
831=head1 SECURITY CONSIDERATIONS 1290=head1 SECURITY CONSIDERATIONS
837any buffer overflows. Obviously, this module should ensure that and I am 1296any buffer overflows. Obviously, this module should ensure that and I am
838trying hard on making that true, but you never know. 1297trying hard on making that true, but you never know.
839 1298
840Second, you need to avoid resource-starving attacks. That means you should 1299Second, you need to avoid resource-starving attacks. That means you should
841limit the size of JSON texts you accept, or make sure then when your 1300limit the size of JSON texts you accept, or make sure then when your
842resources run out, thats just fine (e.g. by using a separate process that 1301resources run out, that's just fine (e.g. by using a separate process that
843can crash safely). The size of a JSON text in octets or characters is 1302can crash safely). The size of a JSON text in octets or characters is
844usually a good indication of the size of the resources required to decode 1303usually a good indication of the size of the resources required to decode
845it into a Perl structure. While JSON::XS can check the size of the JSON 1304it into a Perl structure. While JSON::XS can check the size of the JSON
846text, it might be too late when you already have it in memory, so you 1305text, it might be too late when you already have it in memory, so you
847might want to check the size before you accept the string. 1306might want to check the size before you accept the string.
848 1307
849Third, JSON::XS recurses using the C stack when decoding objects and 1308Third, JSON::XS recurses using the C stack when decoding objects and
850arrays. The C stack is a limited resource: for instance, on my amd64 1309arrays. The C stack is a limited resource: for instance, on my amd64
851machine with 8MB of stack size I can decode around 180k nested arrays but 1310machine with 8MB of stack size I can decode around 180k nested arrays but
852only 14k nested JSON objects (due to perl itself recursing deeply on croak 1311only 14k nested JSON objects (due to perl itself recursing deeply on croak
853to free the temporary). If that is exceeded, the program crashes. to be 1312to free the temporary). If that is exceeded, the program crashes. To be
854conservative, the default nesting limit is set to 512. If your process 1313conservative, the default nesting limit is set to 512. If your process
855has a smaller stack, you should adjust this setting accordingly with the 1314has a smaller stack, you should adjust this setting accordingly with the
856C<max_depth> method. 1315C<max_depth> method.
857 1316
858And last but least, something else could bomb you that I forgot to think 1317Something else could bomb you, too, that I forgot to think of. In that
859of. In that case, you get to keep the pieces. I am always open for hints, 1318case, you get to keep the pieces. I am always open for hints, though...
860though... 1319
1320Also keep in mind that JSON::XS might leak contents of your Perl data
1321structures in its error messages, so when you serialise sensitive
1322information you might want to make sure that exceptions thrown by JSON::XS
1323will not end up in front of untrusted eyes.
861 1324
862If you are using JSON::XS to return packets to consumption 1325If you are using JSON::XS to return packets to consumption
863by javascript scripts in a browser you should have a look at 1326by JavaScript scripts in a browser you should have a look at
864L<http://jpsykes.com/47/practical-csrf-and-json-security> to see wether 1327L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
865you are vulnerable to some common attack vectors (which really are browser 1328you are vulnerable to some common attack vectors (which really are browser
866design bugs, but it is still you who will have to deal with it, as major 1329design bugs, but it is still you who will have to deal with it, as major
867browser developers care only for features, not about doing security 1330browser developers care only for features, not about getting security
868right). 1331right).
869 1332
870 1333
1334=head1 THREADS
1335
1336This module is I<not> guaranteed to be thread safe and there are no
1337plans to change this until Perl gets thread support (as opposed to the
1338horribly slow so-called "threads" which are simply slow and bloated
1339process simulations - use fork, it's I<much> faster, cheaper, better).
1340
1341(It might actually work, but you have been warned).
1342
1343
871=head1 BUGS 1344=head1 BUGS
872 1345
873While the goal of this module is to be correct, that unfortunately does 1346While the goal of this module is to be correct, that unfortunately does
874not mean its bug-free, only that I think its design is bug-free. It is 1347not mean it's bug-free, only that I think its design is bug-free. If you
875still relatively early in its development. If you keep reporting bugs they 1348keep reporting bugs they will be fixed swiftly, though.
876will be fixed swiftly, though. 1349
1350Please refrain from using rt.cpan.org or any other bug reporting
1351service. I put the contact address into my modules for a reason.
877 1352
878=cut 1353=cut
879 1354
880our $true = do { bless \(my $dummy = "1"), "JSON::XS::Boolean" }; 1355our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
881our $false = do { bless \(my $dummy = "0"), "JSON::XS::Boolean" }; 1356our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
882 1357
883sub true() { $true } 1358sub true() { $true }
884sub false() { $false } 1359sub false() { $false }
885 1360
886sub is_bool($) { 1361sub is_bool($) {
898 "--" => sub { $_[0] = ${$_[0]} - 1 }, 1373 "--" => sub { $_[0] = ${$_[0]} - 1 },
899 fallback => 1; 1374 fallback => 1;
900 1375
9011; 13761;
902 1377
1378=head1 SEE ALSO
1379
1380The F<json_xs> command line utility for quick experiments.
1381
903=head1 AUTHOR 1382=head1 AUTHOR
904 1383
905 Marc Lehmann <schmorp@schmorp.de> 1384 Marc Lehmann <schmorp@schmorp.de>
906 http://home.schmorp.de/ 1385 http://home.schmorp.de/
907 1386

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