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Revision 1.47 by root, Mon Jun 25 06:57:42 2007 UTC vs.
Revision 1.102 by root, Sat Apr 19 03:39:27 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
15 # objToJson and jsonToObj aliases to to_json and from_json
16 # are exported for compatibility to the JSON module,
17 # but should not be used in new code.
18 19
19 # OO-interface 20 # OO-interface
20 21
21 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 22 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
22 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 23 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
23 $perl_scalar = $coder->decode ($unicode_json_text); 24 $perl_scalar = $coder->decode ($unicode_json_text);
24 25
26 # Note that JSON version 2.0 and above will automatically use JSON::XS
27 # if available, at virtually no speed overhead either, so you should
28 # be able to just:
29
30 use JSON;
31
32 # and do the same things, except that you have a pure-perl fallback now.
33
25=head1 DESCRIPTION 34=head1 DESCRIPTION
26 35
27This module converts Perl data structures to JSON and vice versa. Its 36This module converts Perl data structures to JSON and vice versa. Its
28primary 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
29I<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.
30 47
31As 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
32to 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
33modules, 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
34their maintainers are unresponsive, gone missing, or not listening to bug 51their maintainers are unresponsive, gone missing, or not listening to bug
41 58
42=head2 FEATURES 59=head2 FEATURES
43 60
44=over 4 61=over 4
45 62
46=item * correct unicode handling 63=item * correct Unicode handling
47 64
48This 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
49it does so. 66so, and even documents what "correct" means.
50 67
51=item * round-trip integrity 68=item * round-trip integrity
52 69
53When you serialise a perl data structure using only datatypes supported 70When you serialise a perl data structure using only datatypes supported
54by JSON, the deserialised data structure is identical on the Perl level. 71by JSON, the deserialised data structure is identical on the Perl level.
55(e.g. the string "2.0" doesn't suddenly become "2" just because it looks 72(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
56like a number). 73like a number). There minor I<are> exceptions to this, read the MAPPING
74section below to learn about those.
57 75
58=item * strict checking of JSON correctness 76=item * strict checking of JSON correctness
59 77
60There is no guessing, no generating of illegal JSON texts by default, 78There is no guessing, no generating of illegal JSON texts by default,
61and 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
62feature). 80feature).
63 81
64=item * fast 82=item * fast
65 83
66Compared to other JSON modules, this module compares favourably in terms 84Compared to other JSON modules and other serialisers such as Storable,
67of speed, too. 85this module usually compares favourably in terms of speed, too.
68 86
69=item * simple to use 87=item * simple to use
70 88
71This 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
72interface. 90oriented interface interface.
73 91
74=item * reasonably versatile output formats 92=item * reasonably versatile output formats
75 93
76You can choose between the most compact guarenteed single-line format 94You can choose between the most compact guaranteed-single-line format
77possible (nice for simple line-based protocols), a pure-ascii format 95possible (nice for simple line-based protocols), a pure-ascii format
78(for when your transport is not 8-bit clean, still supports the whole 96(for when your transport is not 8-bit clean, still supports the whole
79unicode 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
80stuff). Or you can combine those features in whatever way you like. 98stuff). Or you can combine those features in whatever way you like.
81 99
82=back 100=back
83 101
84=cut 102=cut
85 103
86package JSON::XS; 104package JSON::XS;
87 105
88use strict; 106use strict;
89 107
90our $VERSION = '1.4'; 108our $VERSION = '2.2';
91our @ISA = qw(Exporter); 109our @ISA = qw(Exporter);
92 110
93our @EXPORT = qw(to_json from_json objToJson jsonToObj); 111our @EXPORT = qw(encode_json decode_json to_json from_json);
112
113sub to_json($) {
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}
94 122
95use Exporter; 123use Exporter;
96use XSLoader; 124use XSLoader;
97 125
98=head1 FUNCTIONAL INTERFACE 126=head1 FUNCTIONAL INTERFACE
99 127
100The following convinience methods are provided by this module. They are 128The following convenience methods are provided by this module. They are
101exported by default: 129exported by default:
102 130
103=over 4 131=over 4
104 132
105=item $json_text = to_json $perl_scalar 133=item $json_text = encode_json $perl_scalar
106 134
107Converts 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
108a 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.
109octets only). Croaks on error.
110 137
111This function call is functionally identical to: 138This function call is functionally identical to:
112 139
113 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 140 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
114 141
115except being faster. 142except being faster.
116 143
117=item $perl_scalar = from_json $json_text 144=item $perl_scalar = decode_json $json_text
118 145
119The 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
120parse 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
121scalar or reference. Croaks on error. 148reference. Croaks on error.
122 149
123This function call is functionally identical to: 150This function call is functionally identical to:
124 151
125 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 152 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
126 153
136Perl. 163Perl.
137 164
138=back 165=back
139 166
140 167
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
141=head1 OBJECT-ORIENTED INTERFACE 216=head1 OBJECT-ORIENTED INTERFACE
142 217
143The object oriented interface lets you configure your own encoding or 218The object oriented interface lets you configure your own encoding or
144decoding style, within the limits of supported formats. 219decoding style, within the limits of supported formats.
145 220
156 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]})
157 => {"a": [1, 2]} 232 => {"a": [1, 2]}
158 233
159=item $json = $json->ascii ([$enable]) 234=item $json = $json->ascii ([$enable])
160 235
236=item $enabled = $json->get_ascii
237
161If C<$enable> is true (or missing), then the C<encode> method will not 238If C<$enable> is true (or missing), then the C<encode> method will not
162generate characters outside the code range C<0..127> (which is ASCII). Any 239generate characters outside the code range C<0..127> (which is ASCII). Any
163unicode characters outside that range will be escaped using either a 240Unicode characters outside that range will be escaped using either a
164single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, 241single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
165as per RFC4627. The resulting encoded JSON text can be treated as a native 242as per RFC4627. The resulting encoded JSON text can be treated as a native
166unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string, 243Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
167or any other superset of ASCII. 244or any other superset of ASCII.
168 245
169If C<$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
170characters unless required by the JSON syntax or other flags. This results 247characters unless required by the JSON syntax or other flags. This results
171in a faster and more compact format. 248in a faster and more compact format.
172 249
250See also the section I<ENCODING/CODESET FLAG NOTES> later in this
251document.
252
173The 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
174transmitted 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
175contain any 8 bit characters. 255contain any 8 bit characters.
176 256
177 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 257 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
178 => ["\ud801\udc01"] 258 => ["\ud801\udc01"]
179 259
180=item $json = $json->latin1 ([$enable]) 260=item $json = $json->latin1 ([$enable])
181 261
262=item $enabled = $json->get_latin1
263
182If C<$enable> is true (or missing), then the C<encode> method will encode 264If C<$enable> is true (or missing), then the C<encode> method will encode
183the resulting JSON text as latin1 (or iso-8859-1), escaping any characters 265the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
184outside the code range C<0..255>. The resulting string can be treated as a 266outside the code range C<0..255>. The resulting string can be treated as a
185latin1-encoded JSON text or a native unicode string. The C<decode> method 267latin1-encoded JSON text or a native Unicode string. The C<decode> method
186will not be affected in any way by this flag, as C<decode> by default 268will not be affected in any way by this flag, as C<decode> by default
187expects unicode, which is a strict superset of latin1. 269expects Unicode, which is a strict superset of latin1.
188 270
189If C<$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
190characters 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.
191 276
192The 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
193text, 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
194size. The disadvantage is that the resulting JSON text is encoded 279size. The disadvantage is that the resulting JSON text is encoded
195in latin1 (and must correctly be treated as such when storing and 280in latin1 (and must correctly be treated as such when storing and
196transfering), a rare encoding for JSON. It is therefore most useful when 281transferring), a rare encoding for JSON. It is therefore most useful when
197you want to store data structures known to contain binary data efficiently 282you want to store data structures known to contain binary data efficiently
198in files or databases, not when talking to other JSON encoders/decoders. 283in files or databases, not when talking to other JSON encoders/decoders.
199 284
200 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] 285 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
201 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) 286 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
202 287
203=item $json = $json->utf8 ([$enable]) 288=item $json = $json->utf8 ([$enable])
289
290=item $enabled = $json->get_utf8
204 291
205If C<$enable> is true (or missing), then the C<encode> method will encode 292If C<$enable> is true (or missing), then the C<encode> method will encode
206the JSON result into UTF-8, as required by many protocols, while the 293the JSON result into UTF-8, as required by many protocols, while the
207C<decode> method expects to be handled an UTF-8-encoded string. Please 294C<decode> method expects to be handled an UTF-8-encoded string. Please
208note that UTF-8-encoded strings do not contain any characters outside the 295note that UTF-8-encoded strings do not contain any characters outside the
209range C<0..255>, they are thus useful for bytewise/binary I/O. In future 296range C<0..255>, they are thus useful for bytewise/binary I/O. In future
210versions, enabling this option might enable autodetection of the UTF-16 297versions, enabling this option might enable autodetection of the UTF-16
211and UTF-32 encoding families, as described in RFC4627. 298and UTF-32 encoding families, as described in RFC4627.
212 299
213If C<$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
214string 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
215unicode 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
216to 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.
217 307
218Example, output UTF-16BE-encoded JSON: 308Example, output UTF-16BE-encoded JSON:
219 309
220 use Encode; 310 use Encode;
221 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); 311 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
242 ] 332 ]
243 } 333 }
244 334
245=item $json = $json->indent ([$enable]) 335=item $json = $json->indent ([$enable])
246 336
337=item $enabled = $json->get_indent
338
247If C<$enable> is true (or missing), then the C<encode> method will use a multiline 339If C<$enable> is true (or missing), then the C<encode> method will use a multiline
248format as output, putting every array member or object/hash key-value pair 340format as output, putting every array member or object/hash key-value pair
249into its own line, identing them properly. 341into its own line, indenting them properly.
250 342
251If C<$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
252resulting JSON text is guarenteed not to contain any C<newlines>. 344resulting JSON text is guaranteed not to contain any C<newlines>.
253 345
254This setting has no effect when decoding JSON texts. 346This setting has no effect when decoding JSON texts.
255 347
256=item $json = $json->space_before ([$enable]) 348=item $json = $json->space_before ([$enable])
349
350=item $enabled = $json->get_space_before
257 351
258If C<$enable> is true (or missing), then the C<encode> method will add an extra 352If C<$enable> is true (or missing), then the C<encode> method will add an extra
259optional space before the C<:> separating keys from values in JSON objects. 353optional space before the C<:> separating keys from values in JSON objects.
260 354
261If C<$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
267Example, space_before enabled, space_after and indent disabled: 361Example, space_before enabled, space_after and indent disabled:
268 362
269 {"key" :"value"} 363 {"key" :"value"}
270 364
271=item $json = $json->space_after ([$enable]) 365=item $json = $json->space_after ([$enable])
366
367=item $enabled = $json->get_space_after
272 368
273If C<$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
274optional space after the C<:> separating keys from values in JSON objects 370optional space after the C<:> separating keys from values in JSON objects
275and extra whitespace after the C<,> separating key-value pairs and array 371and extra whitespace after the C<,> separating key-value pairs and array
276members. 372members.
282 378
283Example, space_before and indent disabled, space_after enabled: 379Example, space_before and indent disabled, space_after enabled:
284 380
285 {"key": "value"} 381 {"key": "value"}
286 382
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
287=item $json = $json->canonical ([$enable]) 430=item $json = $json->canonical ([$enable])
431
432=item $enabled = $json->get_canonical
288 433
289If C<$enable> is true (or missing), then the C<encode> method will output JSON objects 434If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
290by sorting their keys. This is adding a comparatively high overhead. 435by sorting their keys. This is adding a comparatively high overhead.
291 436
292If C<$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
293pairs 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
294of the same script). 439of the same script).
295 440
296This 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
297the 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,
298the 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,
299as key-value pairs have no inherent ordering in Perl. 444as key-value pairs have no inherent ordering in Perl.
300 445
301This setting has no effect when decoding JSON texts. 446This setting has no effect when decoding JSON texts.
302 447
303=item $json = $json->allow_nonref ([$enable]) 448=item $json = $json->allow_nonref ([$enable])
449
450=item $enabled = $json->get_allow_nonref
304 451
305If C<$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
306non-reference into its corresponding string, number or null JSON value, 453non-reference into its corresponding string, number or null JSON value,
307which 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
308values instead of croaking. 455values instead of croaking.
316resulting in an invalid JSON text: 463resulting in an invalid JSON text:
317 464
318 JSON::XS->new->allow_nonref->encode ("Hello, World!") 465 JSON::XS->new->allow_nonref->encode ("Hello, World!")
319 => "Hello, World!" 466 => "Hello, World!"
320 467
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
321=item $json = $json->allow_blessed ([$enable]) 484=item $json = $json->allow_blessed ([$enable])
485
486=item $enabled = $json->get_allow_blessed
322 487
323If C<$enable> is true (or missing), then the C<encode> method will not 488If C<$enable> is true (or missing), then the C<encode> method will not
324barf when it encounters a blessed reference. Instead, the value of the 489barf when it encounters a blessed reference. Instead, the value of the
325B<convert_blessed> option will decide wether C<null> (C<convert_blessed> 490B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
326disabled or no C<to_json> method found) or a representation of the 491disabled or no C<TO_JSON> method found) or a representation of the
327object (C<convert_blessed> enabled and C<to_json> method found) is being 492object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
328encoded. Has no effect on C<decode>. 493encoded. Has no effect on C<decode>.
329 494
330If C<$enable> is false (the default), then C<encode> will throw an 495If C<$enable> is false (the default), then C<encode> will throw an
331exception when it encounters a blessed object. 496exception when it encounters a blessed object.
332 497
333=item $json = $json->convert_blessed ([$enable]) 498=item $json = $json->convert_blessed ([$enable])
499
500=item $enabled = $json->get_convert_blessed
334 501
335If C<$enable> is true (or missing), then C<encode>, upon encountering a 502If C<$enable> is true (or missing), then C<encode>, upon encountering a
336blessed object, will check for the availability of the C<TO_JSON> method 503blessed object, will check for the availability of the C<TO_JSON> method
337on the object's class. If found, it will be called in scalar context 504on the object's class. If found, it will be called in scalar context
338and the resulting scalar will be encoded instead of the object. If no 505and the resulting scalar will be encoded instead of the object. If no
342The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON> 509The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
343returns other blessed objects, those will be handled in the same 510returns other blessed objects, those will be handled in the same
344way. C<TO_JSON> must take care of not causing an endless recursion cycle 511way. C<TO_JSON> must take care of not causing an endless recursion cycle
345(== crash) in this case. The name of C<TO_JSON> was chosen because other 512(== crash) in this case. The name of C<TO_JSON> was chosen because other
346methods called by the Perl core (== not by the user of the object) are 513methods called by the Perl core (== not by the user of the object) are
347usually in upper case letters and to avoid collisions with the C<to_json> 514usually in upper case letters and to avoid collisions with any C<to_json>
348function. 515function or method.
349 516
350This setting does not yet influence C<decode> in any way, but in the 517This setting does not yet influence C<decode> in any way, but in the
351future, global hooks might get installed that influence C<decode> and are 518future, global hooks might get installed that influence C<decode> and are
352enabled by this setting. 519enabled by this setting.
353 520
354If C<$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
355to do when a blessed object is found. 522to do when a blessed object is found.
356 523
524=item $json = $json->filter_json_object ([$coderef->($hashref)])
525
526When C<$coderef> is specified, it will be called from C<decode> each
527time it decodes a JSON object. The only argument is a reference to the
528newly-created hash. If the code references returns a single scalar (which
529need not be a reference), this value (i.e. a copy of that scalar to avoid
530aliasing) is inserted into the deserialised data structure. If it returns
531an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
532original deserialised hash will be inserted. This setting can slow down
533decoding considerably.
534
535When C<$coderef> is omitted or undefined, any existing callback will
536be removed and C<decode> will not change the deserialised hash in any
537way.
538
539Example, convert all JSON objects into the integer 5:
540
541 my $js = JSON::XS->new->filter_json_object (sub { 5 });
542 # returns [5]
543 $js->decode ('[{}]')
544 # throw an exception because allow_nonref is not enabled
545 # so a lone 5 is not allowed.
546 $js->decode ('{"a":1, "b":2}');
547
548=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
549
550Works remotely similar to C<filter_json_object>, but is only called for
551JSON objects having a single key named C<$key>.
552
553This C<$coderef> is called before the one specified via
554C<filter_json_object>, if any. It gets passed the single value in the JSON
555object. If it returns a single value, it will be inserted into the data
556structure. If it returns nothing (not even C<undef> but the empty list),
557the callback from C<filter_json_object> will be called next, as if no
558single-key callback were specified.
559
560If C<$coderef> is omitted or undefined, the corresponding callback will be
561disabled. There can only ever be one callback for a given key.
562
563As this callback gets called less often then the C<filter_json_object>
564one, decoding speed will not usually suffer as much. Therefore, single-key
565objects make excellent targets to serialise Perl objects into, especially
566as single-key JSON objects are as close to the type-tagged value concept
567as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
568support this in any way, so you need to make sure your data never looks
569like a serialised Perl hash.
570
571Typical names for the single object key are C<__class_whatever__>, or
572C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
573things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
574with real hashes.
575
576Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
577into the corresponding C<< $WIDGET{<id>} >> object:
578
579 # return whatever is in $WIDGET{5}:
580 JSON::XS
581 ->new
582 ->filter_json_single_key_object (__widget__ => sub {
583 $WIDGET{ $_[0] }
584 })
585 ->decode ('{"__widget__": 5')
586
587 # this can be used with a TO_JSON method in some "widget" class
588 # for serialisation to json:
589 sub WidgetBase::TO_JSON {
590 my ($self) = @_;
591
592 unless ($self->{id}) {
593 $self->{id} = ..get..some..id..;
594 $WIDGET{$self->{id}} = $self;
595 }
596
597 { __widget__ => $self->{id} }
598 }
599
357=item $json = $json->shrink ([$enable]) 600=item $json = $json->shrink ([$enable])
601
602=item $enabled = $json->get_shrink
358 603
359Perl usually over-allocates memory a bit when allocating space for 604Perl usually over-allocates memory a bit when allocating space for
360strings. This flag optionally resizes strings generated by either 605strings. This flag optionally resizes strings generated by either
361C<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
362memory 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
380strings that look like integers or floats into integers or floats 625strings that look like integers or floats into integers or floats
381internally (there is no difference on the Perl level), saving space. 626internally (there is no difference on the Perl level), saving space.
382 627
383=item $json = $json->max_depth ([$maximum_nesting_depth]) 628=item $json = $json->max_depth ([$maximum_nesting_depth])
384 629
630=item $max_depth = $json->get_max_depth
631
385Sets the maximum nesting level (default C<512>) accepted while encoding 632Sets the maximum nesting level (default C<512>) accepted while encoding
386or 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
387higher nesting level then this limit, then the encoder and decoder will 634data structure, then the encoder and decoder will stop and croak at that
388stop and croak at that point. 635point.
389 636
390Nesting 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
391needs 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<[>
392characters without their matching closing parenthesis crossed to reach a 639characters without their matching closing parenthesis crossed to reach a
393given character in a string. 640given character in a string.
394 641
395Setting the maximum depth to one disallows any nesting, so that ensures 642Setting the maximum depth to one disallows any nesting, so that ensures
396that the object is only a single hash/object or array. 643that the object is only a single hash/object or array.
397 644
398The argument to C<max_depth> will be rounded up to the next highest power
399of 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
400used, 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.
401 651
402See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 652See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
403 653
404=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
405 657
406Set 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
407being 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>
408is 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
409attempt 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
410effect on C<encode> (yet). 662effect on C<encode> (yet).
411 663
412The 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
413power of two (so may be more than requested). If no argument is given, the 665C<0> is specified).
414limit check will be deactivated (same as when C<0> is specified).
415 666
416See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 667See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
417 668
418=item $json_text = $json->encode ($perl_scalar) 669=item $json_text = $json->encode ($perl_scalar)
419 670
448 => ([], 3) 699 => ([], 3)
449 700
450=back 701=back
451 702
452 703
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
453=head1 MAPPING 924=head1 MAPPING
454 925
455This 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
456vice 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
457circumstances automatically, preserving round-tripping characteristics 928circumstances automatically, preserving round-tripping characteristics
458(what you put in comes out as something equivalent). 929(what you put in comes out as something equivalent).
459 930
460For the more enlightened: note that in the following descriptions, 931For the more enlightened: note that in the following descriptions,
461lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl> 932lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
462refers to the abstract Perl language itself. 933refers to the abstract Perl language itself.
463 934
464 935
465=head2 JSON -> PERL 936=head2 JSON -> PERL
466 937
467=over 4 938=over 4
468 939
469=item object 940=item object
470 941
471A 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
472keys is preserved (JSON does not preserver object key ordering itself). 943keys is preserved (JSON does not preserve object key ordering itself).
473 944
474=item array 945=item array
475 946
476A JSON array becomes a reference to an array in Perl. 947A JSON array becomes a reference to an array in Perl.
477 948
481are 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
482decoding is necessary. 953decoding is necessary.
483 954
484=item number 955=item number
485 956
486A JSON number becomes either an integer or numeric (floating point) 957A JSON number becomes either an integer, numeric (floating point) or
487scalar 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
488Perl 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
489conversion details, but an integer may take slightly less memory and might 960the conversion details, but an integer may take slightly less memory and
490represent 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).
491 974
492=item true, false 975=item true, false
493 976
494These 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>,
495respectively. They are overloaded to act almost exactly like the numbers 978respectively. They are overloaded to act almost exactly like the numbers
496C<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
497the C<JSON::XS::is_bool> function. 980the C<JSON::XS::is_bool> function.
498 981
499=item null 982=item null
500 983
501A JSON null atom becomes C<undef> in Perl. 984A JSON null atom becomes C<undef> in Perl.
532Other unblessed references are generally not allowed and will cause an 1015Other unblessed references are generally not allowed and will cause an
533exception 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
534C<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
535also 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.
536 1019
537 to_json [\0,JSON::XS::true] # yields [false,true] 1020 encode_json [\0,JSON::XS::true] # yields [false,true]
538 1021
539=item JSON::XS::true, JSON::XS::false 1022=item JSON::XS::true, JSON::XS::false
540 1023
541These special values become JSON true and JSON false values, 1024These special values become JSON true and JSON false values,
542respectively. 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.
543 1026
544=item blessed objects 1027=item blessed objects
545 1028
546Blessed objects are not allowed. JSON::XS currently tries to encode their 1029Blessed objects are not directly representable in JSON. See the
547underlying representation (hash- or arrayref), but this behaviour might 1030C<allow_blessed> and C<convert_blessed> methods on various options on
548change 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.
549 1034
550=item simple scalars 1035=item simple scalars
551 1036
552Simple 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
553difficult objects to encode: JSON::XS will encode undefined scalars as 1038difficult objects to encode: JSON::XS will encode undefined scalars as
554JSON 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
555before encoding as JSON strings and anything else as number value: 1040before encoding as JSON strings, and anything else as number value:
556 1041
557 # dump as number 1042 # dump as number
558 to_json [2] # yields [2] 1043 encode_json [2] # yields [2]
559 to_json [-3.0e17] # yields [-3e+17] 1044 encode_json [-3.0e17] # yields [-3e+17]
560 my $value = 5; to_json [$value] # yields [5] 1045 my $value = 5; encode_json [$value] # yields [5]
561 1046
562 # used as string, so dump as string 1047 # used as string, so dump as string
563 print $value; 1048 print $value;
564 to_json [$value] # yields ["5"] 1049 encode_json [$value] # yields ["5"]
565 1050
566 # undef becomes null 1051 # undef becomes null
567 to_json [undef] # yields [null] 1052 encode_json [undef] # yields [null]
568 1053
569You can force the type to be a string by stringifying it: 1054You can force the type to be a JSON string by stringifying it:
570 1055
571 my $x = 3.1; # some variable containing a number 1056 my $x = 3.1; # some variable containing a number
572 "$x"; # stringified 1057 "$x"; # stringified
573 $x .= ""; # another, more awkward way to stringify 1058 $x .= ""; # another, more awkward way to stringify
574 print $x; # perl does it for you, too, quite often 1059 print $x; # perl does it for you, too, quite often
575 1060
576You can force the type to be a number by numifying it: 1061You can force the type to be a JSON number by numifying it:
577 1062
578 my $x = "3"; # some variable containing a string 1063 my $x = "3"; # some variable containing a string
579 $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
580 $x *= 1; # same thing, the choise is yours. 1065 $x *= 1; # same thing, the choice is yours.
581 1066
582You 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
583less 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:).
584 1070
585=back 1071=back
586 1072
587 1073
588=head1 COMPARISON 1074=head1 ENCODING/CODESET FLAG NOTES
589 1075
590As already mentioned, this module was created because none of the existing 1076The interested reader might have seen a number of flags that signify
591JSON 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
592problems (or pleasures) I encountered with various existing JSON modules, 1078some confusion on what these do, so here is a short comparison:
593followed by some benchmark values. JSON::XS was designed not to suffer 1079
594from 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.
595 1098
596=over 4 1099=over 4
597 1100
598=item JSON 1.07 1101=item C<utf8> flag disabled
599 1102
600Slow (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).
601 1110
602Undocumented/buggy Unicode handling (how JSON handles unicode values is 1111This is useful when you want to do the encoding yourself (e.g. when you
603undocumented. 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
604en-/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).
605 1116
606No roundtripping (strings get clobbered if they look like numbers, e.g. 1117=item C<utf8> flag enabled
607the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
608decode into the number 2.
609 1118
610=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.
611 1124
612Very 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.
613 1128
614Undocumented/buggy Unicode handling. 1129=item C<latin1> or C<ascii> flags enabled
615 1130
616No 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.
617 1134
618Has 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
619values 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).
620 1140
621Does 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,
622which is not a valid JSON text. 1142regardless of these flags, just some more characters will be escaped using
1143C<\uXXXX> then before.
623 1144
624Unmaintained (maintainer unresponsive for many months, bugs are not 1145Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
625getting 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.
626 1149
627=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.
628 1154
629Very 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.
630 1157
631Very inflexible (no human-readable format supported, format pretty much 1158The main use for C<latin1> is to relatively efficiently store binary data
632undocumented. 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.
633single-line compact format for use in a protocol, and preferably a way to
634generate ASCII-only JSON texts).
635 1160
636Completely broken (and confusingly documented) Unicode handling (unicode 1161The main use for C<ascii> is to force the output to not contain characters
637escapes are not working properly, you need to set ImplicitUnicode to 1162with values > 127, which means you can interpret the resulting string
638I<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
639 11648-bit-encoding, and still get the same data structure back. This is useful
640No 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
641value was used in a numeric context or not). 1166might be mangled in between (e.g. in mail), and works because ASCII is a
642 1167proper subset of most 8-bit and multibyte encodings in use in the world.
643Dumping hashes may skip hash values depending on iterator state.
644
645Unmaintained (maintainer unresponsive for many months, bugs are not
646getting fixed).
647
648Does not check input for validity (i.e. will accept non-JSON input and
649return "something" instead of raising an exception. This is a security
650issue: imagine two banks transfering money between each other using
651JSON. One bank might parse a given non-JSON request and deduct money,
652while the other might reject the transaction with a syntax error. While a
653good protocol will at least recover, that is extra unnecessary work and
654the transaction will still not succeed).
655
656=item JSON::DWIW 0.04
657
658Very fast. Very natural. Very nice.
659
660Undocumented unicode handling (but the best of the pack. Unicode escapes
661still don't get parsed properly).
662
663Very inflexible.
664
665No roundtripping.
666
667Does not generate valid JSON texts (key strings are often unquoted, empty keys
668result in nothing being output)
669
670Does not check input for validity.
671 1168
672=back 1169=back
673 1170
674 1171
675=head2 JSON and YAML 1172=head2 JSON and YAML
676 1173
677You 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
678however, 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),
679no 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.
680 1179
681If 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
682algorithm (subject to change in future versions): 1181algorithm (subject to change in future versions):
683 1182
684 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1183 my $to_yaml = JSON::XS->new->utf8->space_after (1);
685 my $yaml = $to_yaml->encode ($ref) . "\n"; 1184 my $yaml = $to_yaml->encode ($ref) . "\n";
686 1185
687This will usually generate JSON texts that also parse as valid 1186This will I<usually> generate JSON texts that also parse as valid
688YAML. Please note that YAML has hardcoded limits on (simple) object key 1187YAML. Please note that YAML has hardcoded limits on (simple) object key
689lengths 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
690keys 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).
691 1195
692There 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
693you 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
694or 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
695that 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
696 1224
697 1225
698=head2 SPEED 1226=head2 SPEED
699 1227
700It 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
701tables. 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
702in 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
703system. 1231system.
704 1232
705First comes a comparison between various modules using a very short 1233First comes a comparison between various modules using
706single-line JSON string: 1234a very short single-line JSON string (also available at
1235L<http://dist.schmorp.de/misc/json/short.json>).
707 1236
708 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1237 {"method": "handleMessage", "params": ["user1",
709 "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]}
710 1240
711It shows the number of encodes/decodes per second (JSON::XS uses 1241It shows the number of encodes/decodes per second (JSON::XS uses
712the functional interface, while JSON::XS/2 uses the OO interface 1242the functional interface, while JSON::XS/2 uses the OO interface
713with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables 1243with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
714shrink). Higher is better: 1244shrink). Higher is better:
715 1245
716 module | encode | decode | 1246 module | encode | decode |
717 -----------|------------|------------| 1247 -----------|------------|------------|
718 JSON | 7645.468 | 4208.613 | 1248 JSON 1.x | 4990.842 | 4088.813 |
719 JSON::DWIW | 40721.398 | 77101.176 | 1249 JSON::DWIW | 51653.990 | 71575.154 |
720 JSON::PC | 65948.176 | 78251.940 | 1250 JSON::PC | 65948.176 | 74631.744 |
721 JSON::Syck | 22844.793 | 26479.192 | 1251 JSON::PP | 8931.652 | 3817.168 |
1252 JSON::Syck | 24877.248 | 27776.848 |
722 JSON::XS | 388361.481 | 199728.762 | 1253 JSON::XS | 388361.481 | 227951.304 |
723 JSON::XS/2 | 218453.333 | 192399.266 | 1254 JSON::XS/2 | 227951.304 | 218453.333 |
724 JSON::XS/3 | 338250.323 | 192399.266 | 1255 JSON::XS/3 | 338250.323 | 218453.333 |
725 Storable | 15779.925 | 14169.946 | 1256 Storable | 16500.016 | 135300.129 |
726 -----------+------------+------------+ 1257 -----------+------------+------------+
727 1258
728That 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,
729about three times faster on decoding, and over fourty times faster 1260about three times faster on decoding, and over forty times faster
730than JSON, even with pretty-printing and key sorting. It also compares 1261than JSON, even with pretty-printing and key sorting. It also compares
731favourably to Storable for small amounts of data. 1262favourably to Storable for small amounts of data.
732 1263
733Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1264Using a longer test string (roughly 18KB, generated from Yahoo! Locals
734search API (http://nanoref.com/yahooapis/mgPdGg): 1265search API (L<http://dist.schmorp.de/misc/json/long.json>).
735 1266
736 module | encode | decode | 1267 module | encode | decode |
737 -----------|------------|------------| 1268 -----------|------------|------------|
738 JSON | 254.685 | 37.665 | 1269 JSON 1.x | 55.260 | 34.971 |
739 JSON::DWIW | 843.343 | 1049.731 | 1270 JSON::DWIW | 825.228 | 1082.513 |
740 JSON::PC | 3602.116 | 2307.352 | 1271 JSON::PC | 3571.444 | 2394.829 |
1272 JSON::PP | 210.987 | 32.574 |
741 JSON::Syck | 505.107 | 787.899 | 1273 JSON::Syck | 552.551 | 787.544 |
742 JSON::XS | 5747.196 | 3690.220 | 1274 JSON::XS | 5780.463 | 4854.519 |
743 JSON::XS/2 | 3968.121 | 3676.634 | 1275 JSON::XS/2 | 3869.998 | 4798.975 |
744 JSON::XS/3 | 6105.246 | 3662.508 | 1276 JSON::XS/3 | 5862.880 | 4798.975 |
745 Storable | 4417.337 | 5285.161 | 1277 Storable | 4445.002 | 5235.027 |
746 -----------+------------+------------+ 1278 -----------+------------+------------+
747 1279
748Again, JSON::XS leads by far (except for Storable which non-surprisingly 1280Again, JSON::XS leads by far (except for Storable which non-surprisingly
749decodes faster). 1281decodes faster).
750 1282
751On large strings containing lots of high unicode characters, some modules 1283On large strings containing lots of high Unicode characters, some modules
752(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
753will be broken due to missing (or wrong) unicode handling. Others refuse 1285will be broken due to missing (or wrong) Unicode handling. Others refuse
754to 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
755comparison table for that case. 1287comparison table for that case.
756 1288
757 1289
758=head1 SECURITY CONSIDERATIONS 1290=head1 SECURITY CONSIDERATIONS
764any buffer overflows. Obviously, this module should ensure that and I am 1296any buffer overflows. Obviously, this module should ensure that and I am
765trying hard on making that true, but you never know. 1297trying hard on making that true, but you never know.
766 1298
767Second, you need to avoid resource-starving attacks. That means you should 1299Second, you need to avoid resource-starving attacks. That means you should
768limit 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
769resources 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
770can 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
771usually 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
772it 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
773text, 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
774might want to check the size before you accept the string. 1306might want to check the size before you accept the string.
775 1307
776Third, JSON::XS recurses using the C stack when decoding objects and 1308Third, JSON::XS recurses using the C stack when decoding objects and
777arrays. 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
778machine 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
779only 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
780to 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
781conservative, the default nesting limit is set to 512. If your process 1313conservative, the default nesting limit is set to 512. If your process
782has a smaller stack, you should adjust this setting accordingly with the 1314has a smaller stack, you should adjust this setting accordingly with the
783C<max_depth> method. 1315C<max_depth> method.
784 1316
785And 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
786of. 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...
787though... 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.
788 1324
789If you are using JSON::XS to return packets to consumption 1325If you are using JSON::XS to return packets to consumption
790by javascript scripts in a browser you should have a look at 1326by JavaScript scripts in a browser you should have a look at
791L<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
792you are vulnerable to some common attack vectors (which really are browser 1328you are vulnerable to some common attack vectors (which really are browser
793design 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
794browser developers care only for features, not about doing security 1330browser developers care only for features, not about getting security
795right). 1331right).
796 1332
797 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
798=head1 BUGS 1344=head1 BUGS
799 1345
800While 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
801not 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. It is
802still relatively early in its development. If you keep reporting bugs they 1348still relatively early in its development. If you keep reporting bugs they
803will be fixed swiftly, though. 1349will be fixed swiftly, though.
1350
1351Please refrain from using rt.cpan.org or any other bug reporting
1352service. I put the contact address into my modules for a reason.
804 1353
805=cut 1354=cut
806 1355
807our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" }; 1356our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
808our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" }; 1357our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
825 "--" => sub { $_[0] = ${$_[0]} - 1 }, 1374 "--" => sub { $_[0] = ${$_[0]} - 1 },
826 fallback => 1; 1375 fallback => 1;
827 1376
8281; 13771;
829 1378
1379=head1 SEE ALSO
1380
1381The F<json_xs> command line utility for quick experiments.
1382
830=head1 AUTHOR 1383=head1 AUTHOR
831 1384
832 Marc Lehmann <schmorp@schmorp.de> 1385 Marc Lehmann <schmorp@schmorp.de>
833 http://home.schmorp.de/ 1386 http://home.schmorp.de/
834 1387

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