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Revision 1.23 by root, Sun Mar 25 21:19:13 2007 UTC vs.
Revision 1.75 by root, Thu Nov 29 13:35:35 2007 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
5JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
6 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
4 7
5=head1 SYNOPSIS 8=head1 SYNOPSIS
6 9
7 use JSON::XS; 10 use JSON::XS;
8 11
9 # exported functions, they croak on error 12 # exported functions, they croak on error
10 # and expect/generate UTF-8 13 # and expect/generate UTF-8
11 14
12 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 15 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
13 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 16 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text;
14
15 # objToJson and jsonToObj aliases to to_json and from_json
16 # are exported for compatibility to the JSON module,
17 # but should not be used in new code.
18 17
19 # OO-interface 18 # OO-interface
20 19
21 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 20 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
22 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 21 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
… …
41 40
42=head2 FEATURES 41=head2 FEATURES
43 42
44=over 4 43=over 4
45 44
46=item * correct unicode handling 45=item * correct Unicode handling
47 46
48This module knows how to handle Unicode, and even documents how and when 47This module knows how to handle Unicode, and even documents how and when
49it does so. 48it does so.
50 49
51=item * round-trip integrity 50=item * round-trip integrity
… …
71This module has both a simple functional interface as well as an OO 70This module has both a simple functional interface as well as an OO
72interface. 71interface.
73 72
74=item * reasonably versatile output formats 73=item * reasonably versatile output formats
75 74
76You can choose between the most compact guarenteed single-line format 75You can choose between the most compact guaranteed single-line format
77possible (nice for simple line-based protocols), a pure-ascii format 76possible (nice for simple line-based protocols), a pure-ascii format
78(for when your transport is not 8-bit clean, still supports the whole 77(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 78Unicode 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. 79stuff). Or you can combine those features in whatever way you like.
81 80
82=back 81=back
83 82
84=cut 83=cut
85 84
86package JSON::XS; 85package JSON::XS;
87 86
88use strict; 87use strict;
89 88
90BEGIN {
91 our $VERSION = '0.8'; 89our $VERSION = '2.0';
92 our @ISA = qw(Exporter); 90our @ISA = qw(Exporter);
93 91
94 our @EXPORT = qw(to_json from_json objToJson jsonToObj); 92our @EXPORT = qw(to_json from_json);
95 require Exporter;
96 93
97 require XSLoader; 94use Exporter;
98 XSLoader::load JSON::XS::, $VERSION; 95use XSLoader;
99}
100 96
101=head1 FUNCTIONAL INTERFACE 97=head1 FUNCTIONAL INTERFACE
102 98
103The following convinience methods are provided by this module. They are 99The following convenience methods are provided by this module. They are
104exported by default: 100exported by default:
105 101
106=over 4 102=over 4
107 103
108=item $json_text = to_json $perl_scalar 104=item $json_text = to_json $perl_scalar
109 105
110Converts the given Perl data structure (a simple scalar or a reference to 106Converts the given Perl data structure to a UTF-8 encoded, binary string
111a hash or array) to a UTF-8 encoded, binary string (that is, the string contains 107(that is, the string contains octets only). Croaks on error.
112octets only). Croaks on error.
113 108
114This function call is functionally identical to: 109This function call is functionally identical to:
115 110
116 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 111 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
117 112
118except being faster. 113except being faster.
119 114
120=item $perl_scalar = from_json $json_text 115=item $perl_scalar = from_json $json_text
121 116
122The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to 117The opposite of C<to_json>: expects an UTF-8 (binary) string and tries
123parse that as an UTF-8 encoded JSON text, returning the resulting simple 118to parse that as an UTF-8 encoded JSON text, returning the resulting
124scalar or reference. Croaks on error. 119reference. Croaks on error.
125 120
126This function call is functionally identical to: 121This function call is functionally identical to:
127 122
128 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 123 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
129 124
130except being faster. 125except being faster.
131 126
127=item $is_boolean = JSON::XS::is_bool $scalar
128
129Returns true if the passed scalar represents either JSON::XS::true or
130JSON::XS::false, two constants that act like C<1> and C<0>, respectively
131and are used to represent JSON C<true> and C<false> values in Perl.
132
133See MAPPING, below, for more information on how JSON values are mapped to
134Perl.
135
132=back 136=back
137
138
139=head1 A FEW NOTES ON UNICODE AND PERL
140
141Since this often leads to confusion, here are a few very clear words on
142how Unicode works in Perl, modulo bugs.
143
144=over 4
145
146=item 1. Perl strings can store characters with ordinal values > 255.
147
148This enables you to store Unicode characters as single characters in a
149Perl string - very natural.
150
151=item 2. Perl does I<not> associate an encoding with your strings.
152
153Unless you force it to, e.g. when matching it against a regex, or printing
154the scalar to a file, in which case Perl either interprets your string as
155locale-encoded text, octets/binary, or as Unicode, depending on various
156settings. In no case is an encoding stored together with your data, it is
157I<use> that decides encoding, not any magical metadata.
158
159=item 3. The internal utf-8 flag has no meaning with regards to the
160encoding of your string.
161
162Just ignore that flag unless you debug a Perl bug, a module written in
163XS or want to dive into the internals of perl. Otherwise it will only
164confuse you, as, despite the name, it says nothing about how your string
165is encoded. You can have Unicode strings with that flag set, with that
166flag clear, and you can have binary data with that flag set and that flag
167clear. Other possibilities exist, too.
168
169If you didn't know about that flag, just the better, pretend it doesn't
170exist.
171
172=item 4. A "Unicode String" is simply a string where each character can be
173validly interpreted as a Unicode codepoint.
174
175If you have UTF-8 encoded data, it is no longer a Unicode string, but a
176Unicode string encoded in UTF-8, giving you a binary string.
177
178=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
179
180It's a fact. Learn to live with it.
181
182=back
183
184I hope this helps :)
133 185
134 186
135=head1 OBJECT-ORIENTED INTERFACE 187=head1 OBJECT-ORIENTED INTERFACE
136 188
137The object oriented interface lets you configure your own encoding or 189The object oriented interface lets you configure your own encoding or
… …
150 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) 202 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
151 => {"a": [1, 2]} 203 => {"a": [1, 2]}
152 204
153=item $json = $json->ascii ([$enable]) 205=item $json = $json->ascii ([$enable])
154 206
207=item $enabled = $json->get_ascii
208
155If C<$enable> is true (or missing), then the C<encode> method will not 209If C<$enable> is true (or missing), then the C<encode> method will not
156generate characters outside the code range C<0..127> (which is ASCII). Any 210generate characters outside the code range C<0..127> (which is ASCII). Any
157unicode characters outside that range will be escaped using either a 211Unicode characters outside that range will be escaped using either a
158single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, 212single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
159as per RFC4627. 213as per RFC4627. The resulting encoded JSON text can be treated as a native
214Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
215or any other superset of ASCII.
160 216
161If C<$enable> is false, then the C<encode> method will not escape Unicode 217If C<$enable> is false, then the C<encode> method will not escape Unicode
162characters unless required by the JSON syntax. This results in a faster 218characters unless required by the JSON syntax or other flags. This results
163and more compact format. 219in a faster and more compact format.
220
221The main use for this flag is to produce JSON texts that can be
222transmitted over a 7-bit channel, as the encoded JSON texts will not
223contain any 8 bit characters.
164 224
165 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 225 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
166 => ["\ud801\udc01"] 226 => ["\ud801\udc01"]
167 227
228=item $json = $json->latin1 ([$enable])
229
230=item $enabled = $json->get_latin1
231
232If C<$enable> is true (or missing), then the C<encode> method will encode
233the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
234outside the code range C<0..255>. The resulting string can be treated as a
235latin1-encoded JSON text or a native Unicode string. The C<decode> method
236will not be affected in any way by this flag, as C<decode> by default
237expects Unicode, which is a strict superset of latin1.
238
239If C<$enable> is false, then the C<encode> method will not escape Unicode
240characters unless required by the JSON syntax or other flags.
241
242The main use for this flag is efficiently encoding binary data as JSON
243text, as most octets will not be escaped, resulting in a smaller encoded
244size. The disadvantage is that the resulting JSON text is encoded
245in latin1 (and must correctly be treated as such when storing and
246transferring), a rare encoding for JSON. It is therefore most useful when
247you want to store data structures known to contain binary data efficiently
248in files or databases, not when talking to other JSON encoders/decoders.
249
250 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
251 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
252
168=item $json = $json->utf8 ([$enable]) 253=item $json = $json->utf8 ([$enable])
254
255=item $enabled = $json->get_utf8
169 256
170If C<$enable> is true (or missing), then the C<encode> method will encode 257If C<$enable> is true (or missing), then the C<encode> method will encode
171the JSON result into UTF-8, as required by many protocols, while the 258the JSON result into UTF-8, as required by many protocols, while the
172C<decode> method expects to be handled an UTF-8-encoded string. Please 259C<decode> method expects to be handled an UTF-8-encoded string. Please
173note that UTF-8-encoded strings do not contain any characters outside the 260note that UTF-8-encoded strings do not contain any characters outside the
174range C<0..255>, they are thus useful for bytewise/binary I/O. In future 261range C<0..255>, they are thus useful for bytewise/binary I/O. In future
175versions, enabling this option might enable autodetection of the UTF-16 262versions, enabling this option might enable autodetection of the UTF-16
176and UTF-32 encoding families, as described in RFC4627. 263and UTF-32 encoding families, as described in RFC4627.
177 264
178If C<$enable> is false, then the C<encode> method will return the JSON 265If C<$enable> is false, then the C<encode> method will return the JSON
179string as a (non-encoded) unicode string, while C<decode> expects thus a 266string as a (non-encoded) Unicode string, while C<decode> expects thus a
180unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs 267Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
181to be done yourself, e.g. using the Encode module. 268to be done yourself, e.g. using the Encode module.
182 269
183Example, output UTF-16BE-encoded JSON: 270Example, output UTF-16BE-encoded JSON:
184 271
185 use Encode; 272 use Encode;
… …
207 ] 294 ]
208 } 295 }
209 296
210=item $json = $json->indent ([$enable]) 297=item $json = $json->indent ([$enable])
211 298
299=item $enabled = $json->get_indent
300
212If C<$enable> is true (or missing), then the C<encode> method will use a multiline 301If C<$enable> is true (or missing), then the C<encode> method will use a multiline
213format as output, putting every array member or object/hash key-value pair 302format as output, putting every array member or object/hash key-value pair
214into its own line, identing them properly. 303into its own line, indenting them properly.
215 304
216If C<$enable> is false, no newlines or indenting will be produced, and the 305If C<$enable> is false, no newlines or indenting will be produced, and the
217resulting JSON text is guarenteed not to contain any C<newlines>. 306resulting JSON text is guaranteed not to contain any C<newlines>.
218 307
219This setting has no effect when decoding JSON texts. 308This setting has no effect when decoding JSON texts.
220 309
221=item $json = $json->space_before ([$enable]) 310=item $json = $json->space_before ([$enable])
311
312=item $enabled = $json->get_space_before
222 313
223If C<$enable> is true (or missing), then the C<encode> method will add an extra 314If C<$enable> is true (or missing), then the C<encode> method will add an extra
224optional space before the C<:> separating keys from values in JSON objects. 315optional space before the C<:> separating keys from values in JSON objects.
225 316
226If C<$enable> is false, then the C<encode> method will not add any extra 317If C<$enable> is false, then the C<encode> method will not add any extra
… …
232Example, space_before enabled, space_after and indent disabled: 323Example, space_before enabled, space_after and indent disabled:
233 324
234 {"key" :"value"} 325 {"key" :"value"}
235 326
236=item $json = $json->space_after ([$enable]) 327=item $json = $json->space_after ([$enable])
328
329=item $enabled = $json->get_space_after
237 330
238If C<$enable> is true (or missing), then the C<encode> method will add an extra 331If C<$enable> is true (or missing), then the C<encode> method will add an extra
239optional space after the C<:> separating keys from values in JSON objects 332optional space after the C<:> separating keys from values in JSON objects
240and extra whitespace after the C<,> separating key-value pairs and array 333and extra whitespace after the C<,> separating key-value pairs and array
241members. 334members.
… …
247 340
248Example, space_before and indent disabled, space_after enabled: 341Example, space_before and indent disabled, space_after enabled:
249 342
250 {"key": "value"} 343 {"key": "value"}
251 344
345=item $json = $json->relaxed ([$enable])
346
347=item $enabled = $json->get_relaxed
348
349If C<$enable> is true (or missing), then C<decode> will accept some
350extensions to normal JSON syntax (see below). C<encode> will not be
351affected in anyway. I<Be aware that this option makes you accept invalid
352JSON texts as if they were valid!>. I suggest only to use this option to
353parse application-specific files written by humans (configuration files,
354resource files etc.)
355
356If C<$enable> is false (the default), then C<decode> will only accept
357valid JSON texts.
358
359Currently accepted extensions are:
360
361=over 4
362
363=item * list items can have an end-comma
364
365JSON I<separates> array elements and key-value pairs with commas. This
366can be annoying if you write JSON texts manually and want to be able to
367quickly append elements, so this extension accepts comma at the end of
368such items not just between them:
369
370 [
371 1,
372 2, <- this comma not normally allowed
373 ]
374 {
375 "k1": "v1",
376 "k2": "v2", <- this comma not normally allowed
377 }
378
379=item * shell-style '#'-comments
380
381Whenever JSON allows whitespace, shell-style comments are additionally
382allowed. They are terminated by the first carriage-return or line-feed
383character, after which more white-space and comments are allowed.
384
385 [
386 1, # this comment not allowed in JSON
387 # neither this one...
388 ]
389
390=back
391
252=item $json = $json->canonical ([$enable]) 392=item $json = $json->canonical ([$enable])
393
394=item $enabled = $json->get_canonical
253 395
254If C<$enable> is true (or missing), then the C<encode> method will output JSON objects 396If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
255by sorting their keys. This is adding a comparatively high overhead. 397by sorting their keys. This is adding a comparatively high overhead.
256 398
257If C<$enable> is false, then the C<encode> method will output key-value 399If C<$enable> is false, then the C<encode> method will output key-value
258pairs in the order Perl stores them (which will likely change between runs 400pairs in the order Perl stores them (which will likely change between runs
259of the same script). 401of the same script).
260 402
261This option is useful if you want the same data structure to be encoded as 403This option is useful if you want the same data structure to be encoded as
262the same JSON text (given the same overall settings). If it is disabled, 404the same JSON text (given the same overall settings). If it is disabled,
263the same hash migh be encoded differently even if contains the same data, 405the same hash might be encoded differently even if contains the same data,
264as key-value pairs have no inherent ordering in Perl. 406as key-value pairs have no inherent ordering in Perl.
265 407
266This setting has no effect when decoding JSON texts. 408This setting has no effect when decoding JSON texts.
267 409
268=item $json = $json->allow_nonref ([$enable]) 410=item $json = $json->allow_nonref ([$enable])
411
412=item $enabled = $json->get_allow_nonref
269 413
270If C<$enable> is true (or missing), then the C<encode> method can convert a 414If C<$enable> is true (or missing), then the C<encode> method can convert a
271non-reference into its corresponding string, number or null JSON value, 415non-reference into its corresponding string, number or null JSON value,
272which is an extension to RFC4627. Likewise, C<decode> will accept those JSON 416which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
273values instead of croaking. 417values instead of croaking.
… …
281resulting in an invalid JSON text: 425resulting in an invalid JSON text:
282 426
283 JSON::XS->new->allow_nonref->encode ("Hello, World!") 427 JSON::XS->new->allow_nonref->encode ("Hello, World!")
284 => "Hello, World!" 428 => "Hello, World!"
285 429
430=item $json = $json->allow_blessed ([$enable])
431
432=item $enabled = $json->get_allow_blessed
433
434If C<$enable> is true (or missing), then the C<encode> method will not
435barf when it encounters a blessed reference. Instead, the value of the
436B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
437disabled or no C<to_json> method found) or a representation of the
438object (C<convert_blessed> enabled and C<to_json> method found) is being
439encoded. Has no effect on C<decode>.
440
441If C<$enable> is false (the default), then C<encode> will throw an
442exception when it encounters a blessed object.
443
444=item $json = $json->convert_blessed ([$enable])
445
446=item $enabled = $json->get_convert_blessed
447
448If C<$enable> is true (or missing), then C<encode>, upon encountering a
449blessed object, will check for the availability of the C<TO_JSON> method
450on the object's class. If found, it will be called in scalar context
451and the resulting scalar will be encoded instead of the object. If no
452C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
453to do.
454
455The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
456returns other blessed objects, those will be handled in the same
457way. C<TO_JSON> must take care of not causing an endless recursion cycle
458(== crash) in this case. The name of C<TO_JSON> was chosen because other
459methods called by the Perl core (== not by the user of the object) are
460usually in upper case letters and to avoid collisions with the C<to_json>
461function.
462
463This setting does not yet influence C<decode> in any way, but in the
464future, global hooks might get installed that influence C<decode> and are
465enabled by this setting.
466
467If C<$enable> is false, then the C<allow_blessed> setting will decide what
468to do when a blessed object is found.
469
470=item $json = $json->filter_json_object ([$coderef->($hashref)])
471
472When C<$coderef> is specified, it will be called from C<decode> each
473time it decodes a JSON object. The only argument is a reference to the
474newly-created hash. If the code references returns a single scalar (which
475need not be a reference), this value (i.e. a copy of that scalar to avoid
476aliasing) is inserted into the deserialised data structure. If it returns
477an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
478original deserialised hash will be inserted. This setting can slow down
479decoding considerably.
480
481When C<$coderef> is omitted or undefined, any existing callback will
482be removed and C<decode> will not change the deserialised hash in any
483way.
484
485Example, convert all JSON objects into the integer 5:
486
487 my $js = JSON::XS->new->filter_json_object (sub { 5 });
488 # returns [5]
489 $js->decode ('[{}]')
490 # throw an exception because allow_nonref is not enabled
491 # so a lone 5 is not allowed.
492 $js->decode ('{"a":1, "b":2}');
493
494=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
495
496Works remotely similar to C<filter_json_object>, but is only called for
497JSON objects having a single key named C<$key>.
498
499This C<$coderef> is called before the one specified via
500C<filter_json_object>, if any. It gets passed the single value in the JSON
501object. If it returns a single value, it will be inserted into the data
502structure. If it returns nothing (not even C<undef> but the empty list),
503the callback from C<filter_json_object> will be called next, as if no
504single-key callback were specified.
505
506If C<$coderef> is omitted or undefined, the corresponding callback will be
507disabled. There can only ever be one callback for a given key.
508
509As this callback gets called less often then the C<filter_json_object>
510one, decoding speed will not usually suffer as much. Therefore, single-key
511objects make excellent targets to serialise Perl objects into, especially
512as single-key JSON objects are as close to the type-tagged value concept
513as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
514support this in any way, so you need to make sure your data never looks
515like a serialised Perl hash.
516
517Typical names for the single object key are C<__class_whatever__>, or
518C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
519things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
520with real hashes.
521
522Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
523into the corresponding C<< $WIDGET{<id>} >> object:
524
525 # return whatever is in $WIDGET{5}:
526 JSON::XS
527 ->new
528 ->filter_json_single_key_object (__widget__ => sub {
529 $WIDGET{ $_[0] }
530 })
531 ->decode ('{"__widget__": 5')
532
533 # this can be used with a TO_JSON method in some "widget" class
534 # for serialisation to json:
535 sub WidgetBase::TO_JSON {
536 my ($self) = @_;
537
538 unless ($self->{id}) {
539 $self->{id} = ..get..some..id..;
540 $WIDGET{$self->{id}} = $self;
541 }
542
543 { __widget__ => $self->{id} }
544 }
545
286=item $json = $json->shrink ([$enable]) 546=item $json = $json->shrink ([$enable])
287 547
548=item $enabled = $json->get_shrink
549
288Perl usually over-allocates memory a bit when allocating space for 550Perl usually over-allocates memory a bit when allocating space for
289strings. This flag optionally resizes strings generated by either 551strings. This flag optionally resizes strings generated by either
290C<encode> or C<decode> to their minimum size possible. This can save 552C<encode> or C<decode> to their minimum size possible. This can save
291memory when your JSON texts are either very very long or you have many 553memory when your JSON texts are either very very long or you have many
292short strings. It will also try to downgrade any strings to octet-form 554short strings. It will also try to downgrade any strings to octet-form
293if possible: perl stores strings internally either in an encoding called 555if possible: perl stores strings internally either in an encoding called
294UTF-X or in octet-form. The latter cannot store everything but uses less 556UTF-X or in octet-form. The latter cannot store everything but uses less
295space in general. 557space in general (and some buggy Perl or C code might even rely on that
558internal representation being used).
296 559
560The actual definition of what shrink does might change in future versions,
561but it will always try to save space at the expense of time.
562
297If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit, 563If C<$enable> is true (or missing), the string returned by C<encode> will
298while all strings generated by C<decode> will also be shrunk-to-fit. 564be shrunk-to-fit, while all strings generated by C<decode> will also be
565shrunk-to-fit.
299 566
300If C<$enable> is false, then the normal perl allocation algorithms are used. 567If C<$enable> is false, then the normal perl allocation algorithms are used.
301If you work with your data, then this is likely to be faster. 568If you work with your data, then this is likely to be faster.
302 569
303In the future, this setting might control other things, such as converting 570In the future, this setting might control other things, such as converting
304strings that look like integers or floats into integers or floats 571strings that look like integers or floats into integers or floats
305internally (there is no difference on the Perl level), saving space. 572internally (there is no difference on the Perl level), saving space.
306 573
307=item $json = $json->max_depth ([$maximum_nesting_depth]) 574=item $json = $json->max_depth ([$maximum_nesting_depth])
308 575
576=item $max_depth = $json->get_max_depth
577
309Sets the maximum nesting level (default C<8192>) accepted while encoding 578Sets the maximum nesting level (default C<512>) accepted while encoding
310or decoding. If the JSON text or Perl data structure has an equal or 579or decoding. If the JSON text or Perl data structure has an equal or
311higher nesting level then this limit, then the encoder and decoder will 580higher nesting level then this limit, then the encoder and decoder will
312stop and croak at that point. 581stop and croak at that point.
313 582
314Nesting level is defined by number of hash- or arrayrefs that the encoder 583Nesting level is defined by number of hash- or arrayrefs that the encoder
… …
317given character in a string. 586given character in a string.
318 587
319Setting the maximum depth to one disallows any nesting, so that ensures 588Setting the maximum depth to one disallows any nesting, so that ensures
320that the object is only a single hash/object or array. 589that the object is only a single hash/object or array.
321 590
322The argument to C<max_depth> will be rounded up to the next nearest power 591The argument to C<max_depth> will be rounded up to the next highest power
323of two. 592of two. If no argument is given, the highest possible setting will be
593used, which is rarely useful.
594
595See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
596
597=item $json = $json->max_size ([$maximum_string_size])
598
599=item $max_size = $json->get_max_size
600
601Set the maximum length a JSON text may have (in bytes) where decoding is
602being attempted. The default is C<0>, meaning no limit. When C<decode>
603is called on a string longer then this number of characters it will not
604attempt to decode the string but throw an exception. This setting has no
605effect on C<encode> (yet).
606
607The argument to C<max_size> will be rounded up to the next B<highest>
608power of two (so may be more than requested). If no argument is given, the
609limit check will be deactivated (same as when C<0> is specified).
324 610
325See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 611See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
326 612
327=item $json_text = $json->encode ($perl_scalar) 613=item $json_text = $json->encode ($perl_scalar)
328 614
… …
340 626
341JSON numbers and strings become simple Perl scalars. JSON arrays become 627JSON numbers and strings become simple Perl scalars. JSON arrays become
342Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes 628Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
343C<1>, C<false> becomes C<0> and C<null> becomes C<undef>. 629C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
344 630
631=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
632
633This works like the C<decode> method, but instead of raising an exception
634when there is trailing garbage after the first JSON object, it will
635silently stop parsing there and return the number of characters consumed
636so far.
637
638This is useful if your JSON texts are not delimited by an outer protocol
639(which is not the brightest thing to do in the first place) and you need
640to know where the JSON text ends.
641
642 JSON::XS->new->decode_prefix ("[1] the tail")
643 => ([], 3)
644
345=back 645=back
346 646
347 647
348=head1 MAPPING 648=head1 MAPPING
349 649
… …
351vice versa. These mappings are designed to "do the right thing" in most 651vice versa. These mappings are designed to "do the right thing" in most
352circumstances automatically, preserving round-tripping characteristics 652circumstances automatically, preserving round-tripping characteristics
353(what you put in comes out as something equivalent). 653(what you put in comes out as something equivalent).
354 654
355For the more enlightened: note that in the following descriptions, 655For the more enlightened: note that in the following descriptions,
356lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl> 656lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
357refers to the abstract Perl language itself. 657refers to the abstract Perl language itself.
358 658
659
359=head2 JSON -> PERL 660=head2 JSON -> PERL
360 661
361=over 4 662=over 4
362 663
363=item object 664=item object
364 665
365A JSON object becomes a reference to a hash in Perl. No ordering of object 666A JSON object becomes a reference to a hash in Perl. No ordering of object
366keys is preserved (JSON does not preserver object key ordering itself). 667keys is preserved (JSON does not preserve object key ordering itself).
367 668
368=item array 669=item array
369 670
370A JSON array becomes a reference to an array in Perl. 671A JSON array becomes a reference to an array in Perl.
371 672
… …
375are represented by the same codepoints in the Perl string, so no manual 676are represented by the same codepoints in the Perl string, so no manual
376decoding is necessary. 677decoding is necessary.
377 678
378=item number 679=item number
379 680
380A JSON number becomes either an integer or numeric (floating point) 681A JSON number becomes either an integer, numeric (floating point) or
381scalar in perl, depending on its range and any fractional parts. On the 682string scalar in perl, depending on its range and any fractional parts. On
382Perl level, there is no difference between those as Perl handles all the 683the Perl level, there is no difference between those as Perl handles all
383conversion details, but an integer may take slightly less memory and might 684the conversion details, but an integer may take slightly less memory and
384represent more values exactly than (floating point) numbers. 685might represent more values exactly than (floating point) numbers.
686
687If the number consists of digits only, JSON::XS will try to represent
688it as an integer value. If that fails, it will try to represent it as
689a numeric (floating point) value if that is possible without loss of
690precision. Otherwise it will preserve the number as a string value.
691
692Numbers containing a fractional or exponential part will always be
693represented as numeric (floating point) values, possibly at a loss of
694precision.
695
696This might create round-tripping problems as numbers might become strings,
697but as Perl is typeless there is no other way to do it.
385 698
386=item true, false 699=item true, false
387 700
388These JSON atoms become C<0>, C<1>, respectively. Information is lost in 701These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
389this process. Future versions might represent those values differently, 702respectively. They are overloaded to act almost exactly like the numbers
390but they will be guarenteed to act like these integers would normally in 703C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
391Perl. 704the C<JSON::XS::is_bool> function.
392 705
393=item null 706=item null
394 707
395A JSON null atom becomes C<undef> in Perl. 708A JSON null atom becomes C<undef> in Perl.
396 709
397=back 710=back
711
398 712
399=head2 PERL -> JSON 713=head2 PERL -> JSON
400 714
401The mapping from Perl to JSON is slightly more difficult, as Perl is a 715The mapping from Perl to JSON is slightly more difficult, as Perl is a
402truly typeless language, so we can only guess which JSON type is meant by 716truly typeless language, so we can only guess which JSON type is meant by
… …
405=over 4 719=over 4
406 720
407=item hash references 721=item hash references
408 722
409Perl hash references become JSON objects. As there is no inherent ordering 723Perl hash references become JSON objects. As there is no inherent ordering
410in hash keys, they will usually be encoded in a pseudo-random order that 724in hash keys (or JSON objects), they will usually be encoded in a
411can change between runs of the same program but stays generally the same 725pseudo-random order that can change between runs of the same program but
412within a single run of a program. JSON::XS can optionally sort the hash 726stays generally the same within a single run of a program. JSON::XS can
413keys (determined by the I<canonical> flag), so the same datastructure 727optionally sort the hash keys (determined by the I<canonical> flag), so
414will serialise to the same JSON text (given same settings and version of 728the same datastructure will serialise to the same JSON text (given same
415JSON::XS), but this incurs a runtime overhead. 729settings and version of JSON::XS), but this incurs a runtime overhead
730and is only rarely useful, e.g. when you want to compare some JSON text
731against another for equality.
416 732
417=item array references 733=item array references
418 734
419Perl array references become JSON arrays. 735Perl array references become JSON arrays.
736
737=item other references
738
739Other unblessed references are generally not allowed and will cause an
740exception to be thrown, except for references to the integers C<0> and
741C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
742also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
743
744 to_json [\0,JSON::XS::true] # yields [false,true]
745
746=item JSON::XS::true, JSON::XS::false
747
748These special values become JSON true and JSON false values,
749respectively. You can also use C<\1> and C<\0> directly if you want.
420 750
421=item blessed objects 751=item blessed objects
422 752
423Blessed objects are not allowed. JSON::XS currently tries to encode their 753Blessed objects are not allowed. JSON::XS currently tries to encode their
424underlying representation (hash- or arrayref), but this behaviour might 754underlying representation (hash- or arrayref), but this behaviour might
… …
441 to_json [$value] # yields ["5"] 771 to_json [$value] # yields ["5"]
442 772
443 # undef becomes null 773 # undef becomes null
444 to_json [undef] # yields [null] 774 to_json [undef] # yields [null]
445 775
446You can force the type to be a string by stringifying it: 776You can force the type to be a JSON string by stringifying it:
447 777
448 my $x = 3.1; # some variable containing a number 778 my $x = 3.1; # some variable containing a number
449 "$x"; # stringified 779 "$x"; # stringified
450 $x .= ""; # another, more awkward way to stringify 780 $x .= ""; # another, more awkward way to stringify
451 print $x; # perl does it for you, too, quite often 781 print $x; # perl does it for you, too, quite often
452 782
453You can force the type to be a number by numifying it: 783You can force the type to be a JSON number by numifying it:
454 784
455 my $x = "3"; # some variable containing a string 785 my $x = "3"; # some variable containing a string
456 $x += 0; # numify it, ensuring it will be dumped as a number 786 $x += 0; # numify it, ensuring it will be dumped as a number
457 $x *= 1; # same thing, the choise is yours. 787 $x *= 1; # same thing, the choice is yours.
458 788
459You can not currently output JSON booleans or force the type in other, 789You can not currently force the type in other, less obscure, ways. Tell me
460less obscure, ways. Tell me if you need this capability. 790if you need this capability.
461
462=item circular data structures
463
464Those will be encoded until memory or stackspace runs out.
465 791
466=back 792=back
467 793
468 794
469=head1 COMPARISON 795=head1 COMPARISON
… …
478 804
479=item JSON 1.07 805=item JSON 1.07
480 806
481Slow (but very portable, as it is written in pure Perl). 807Slow (but very portable, as it is written in pure Perl).
482 808
483Undocumented/buggy Unicode handling (how JSON handles unicode values is 809Undocumented/buggy Unicode handling (how JSON handles Unicode values is
484undocumented. One can get far by feeding it unicode strings and doing 810undocumented. One can get far by feeding it Unicode strings and doing
485en-/decoding oneself, but unicode escapes are not working properly). 811en-/decoding oneself, but Unicode escapes are not working properly).
486 812
487No roundtripping (strings get clobbered if they look like numbers, e.g. 813No round-tripping (strings get clobbered if they look like numbers, e.g.
488the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will 814the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
489decode into the number 2. 815decode into the number 2.
490 816
491=item JSON::PC 0.01 817=item JSON::PC 0.01
492 818
493Very fast. 819Very fast.
494 820
495Undocumented/buggy Unicode handling. 821Undocumented/buggy Unicode handling.
496 822
497No roundtripping. 823No round-tripping.
498 824
499Has problems handling many Perl values (e.g. regex results and other magic 825Has problems handling many Perl values (e.g. regex results and other magic
500values will make it croak). 826values will make it croak).
501 827
502Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> 828Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
… …
512Very inflexible (no human-readable format supported, format pretty much 838Very inflexible (no human-readable format supported, format pretty much
513undocumented. I need at least a format for easy reading by humans and a 839undocumented. I need at least a format for easy reading by humans and a
514single-line compact format for use in a protocol, and preferably a way to 840single-line compact format for use in a protocol, and preferably a way to
515generate ASCII-only JSON texts). 841generate ASCII-only JSON texts).
516 842
517Completely broken (and confusingly documented) Unicode handling (unicode 843Completely broken (and confusingly documented) Unicode handling (Unicode
518escapes are not working properly, you need to set ImplicitUnicode to 844escapes are not working properly, you need to set ImplicitUnicode to
519I<different> values on en- and decoding to get symmetric behaviour). 845I<different> values on en- and decoding to get symmetric behaviour).
520 846
521No roundtripping (simple cases work, but this depends on wether the scalar 847No round-tripping (simple cases work, but this depends on whether the scalar
522value was used in a numeric context or not). 848value was used in a numeric context or not).
523 849
524Dumping hashes may skip hash values depending on iterator state. 850Dumping hashes may skip hash values depending on iterator state.
525 851
526Unmaintained (maintainer unresponsive for many months, bugs are not 852Unmaintained (maintainer unresponsive for many months, bugs are not
527getting fixed). 853getting fixed).
528 854
529Does not check input for validity (i.e. will accept non-JSON input and 855Does not check input for validity (i.e. will accept non-JSON input and
530return "something" instead of raising an exception. This is a security 856return "something" instead of raising an exception. This is a security
531issue: imagine two banks transfering money between each other using 857issue: imagine two banks transferring money between each other using
532JSON. One bank might parse a given non-JSON request and deduct money, 858JSON. One bank might parse a given non-JSON request and deduct money,
533while the other might reject the transaction with a syntax error. While a 859while the other might reject the transaction with a syntax error. While a
534good protocol will at least recover, that is extra unnecessary work and 860good protocol will at least recover, that is extra unnecessary work and
535the transaction will still not succeed). 861the transaction will still not succeed).
536 862
537=item JSON::DWIW 0.04 863=item JSON::DWIW 0.04
538 864
539Very fast. Very natural. Very nice. 865Very fast. Very natural. Very nice.
540 866
541Undocumented unicode handling (but the best of the pack. Unicode escapes 867Undocumented Unicode handling (but the best of the pack. Unicode escapes
542still don't get parsed properly). 868still don't get parsed properly).
543 869
544Very inflexible. 870Very inflexible.
545 871
546No roundtripping. 872No round-tripping.
547 873
548Does not generate valid JSON texts (key strings are often unquoted, empty keys 874Does not generate valid JSON texts (key strings are often unquoted, empty keys
549result in nothing being output) 875result in nothing being output)
550 876
551Does not check input for validity. 877Does not check input for validity.
552 878
553=back 879=back
880
881
882=head2 JSON and YAML
883
884You often hear that JSON is a subset (or a close subset) of YAML. This is,
885however, a mass hysteria and very far from the truth. In general, there is
886no way to configure JSON::XS to output a data structure as valid YAML.
887
888If you really must use JSON::XS to generate YAML, you should use this
889algorithm (subject to change in future versions):
890
891 my $to_yaml = JSON::XS->new->utf8->space_after (1);
892 my $yaml = $to_yaml->encode ($ref) . "\n";
893
894This will usually generate JSON texts that also parse as valid
895YAML. Please note that YAML has hardcoded limits on (simple) object key
896lengths that JSON doesn't have, so you should make sure that your hash
897keys are noticeably shorter than the 1024 characters YAML allows.
898
899There might be other incompatibilities that I am not aware of. In general
900you should not try to generate YAML with a JSON generator or vice versa,
901or try to parse JSON with a YAML parser or vice versa: chances are high
902that you will run into severe interoperability problems.
903
554 904
555=head2 SPEED 905=head2 SPEED
556 906
557It seems that JSON::XS is surprisingly fast, as shown in the following 907It seems that JSON::XS is surprisingly fast, as shown in the following
558tables. They have been generated with the help of the C<eg/bench> program 908tables. They have been generated with the help of the C<eg/bench> program
559in the JSON::XS distribution, to make it easy to compare on your own 909in the JSON::XS distribution, to make it easy to compare on your own
560system. 910system.
561 911
562First comes a comparison between various modules using a very short JSON 912First comes a comparison between various modules using a very short
563string: 913single-line JSON string:
564 914
565 {"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null} 915 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
916 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
566 917
567It shows the number of encodes/decodes per second (JSON::XS uses the 918It shows the number of encodes/decodes per second (JSON::XS uses
568functional interface, while JSON::XS/2 uses the OO interface with 919the functional interface, while JSON::XS/2 uses the OO interface
569pretty-printing and hashkey sorting enabled). Higher is better: 920with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
921shrink). Higher is better:
570 922
571 module | encode | decode | 923 module | encode | decode |
572 -----------|------------|------------| 924 -----------|------------|------------|
573 JSON | 11488.516 | 7823.035 | 925 JSON 1.x | 4990.842 | 4088.813 |
574 JSON::DWIW | 94708.054 | 129094.260 | 926 JSON::DWIW | 51653.990 | 71575.154 |
575 JSON::PC | 63884.157 | 128528.212 | 927 JSON::PC | 65948.176 | 74631.744 |
576 JSON::Syck | 34898.677 | 42096.911 | 928 JSON::PP | 8931.652 | 3817.168 |
577 JSON::XS | 654027.064 | 396423.669 | 929 JSON::Syck | 24877.248 | 27776.848 |
578 JSON::XS/2 | 371564.190 | 371725.613 | 930 JSON::XS | 388361.481 | 227951.304 |
931 JSON::XS/2 | 227951.304 | 218453.333 |
932 JSON::XS/3 | 338250.323 | 218453.333 |
933 Storable | 16500.016 | 135300.129 |
579 -----------+------------+------------+ 934 -----------+------------+------------+
580 935
581That is, JSON::XS is more than six times faster than JSON::DWIW on 936That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
582encoding, more than three times faster on decoding, and about thirty times 937about three times faster on decoding, and over forty times faster
583faster than JSON, even with pretty-printing and key sorting. 938than JSON, even with pretty-printing and key sorting. It also compares
939favourably to Storable for small amounts of data.
584 940
585Using a longer test string (roughly 18KB, generated from Yahoo! Locals 941Using a longer test string (roughly 18KB, generated from Yahoo! Locals
586search API (http://nanoref.com/yahooapis/mgPdGg): 942search API (http://nanoref.com/yahooapis/mgPdGg):
587 943
588 module | encode | decode | 944 module | encode | decode |
589 -----------|------------|------------| 945 -----------|------------|------------|
590 JSON | 273.023 | 44.674 | 946 JSON 1.x | 55.260 | 34.971 |
591 JSON::DWIW | 1089.383 | 1145.704 | 947 JSON::DWIW | 825.228 | 1082.513 |
592 JSON::PC | 3097.419 | 2393.921 | 948 JSON::PC | 3571.444 | 2394.829 |
593 JSON::Syck | 514.060 | 843.053 | 949 JSON::PP | 210.987 | 32.574 |
594 JSON::XS | 6479.668 | 3636.364 | 950 JSON::Syck | 552.551 | 787.544 |
595 JSON::XS/2 | 3774.221 | 3599.124 | 951 JSON::XS | 5780.463 | 4854.519 |
952 JSON::XS/2 | 3869.998 | 4798.975 |
953 JSON::XS/3 | 5862.880 | 4798.975 |
954 Storable | 4445.002 | 5235.027 |
596 -----------+------------+------------+ 955 -----------+------------+------------+
597 956
598Again, JSON::XS leads by far. 957Again, JSON::XS leads by far (except for Storable which non-surprisingly
958decodes faster).
599 959
600On large strings containing lots of high unicode characters, some modules 960On large strings containing lots of high Unicode characters, some modules
601(such as JSON::PC) seem to decode faster than JSON::XS, but the result 961(such as JSON::PC) seem to decode faster than JSON::XS, but the result
602will be broken due to missing (or wrong) unicode handling. Others refuse 962will be broken due to missing (or wrong) Unicode handling. Others refuse
603to decode or encode properly, so it was impossible to prepare a fair 963to decode or encode properly, so it was impossible to prepare a fair
604comparison table for that case. 964comparison table for that case.
605 965
606 966
607=head1 SECURITY CONSIDERATIONS 967=head1 SECURITY CONSIDERATIONS
… …
613any buffer overflows. Obviously, this module should ensure that and I am 973any buffer overflows. Obviously, this module should ensure that and I am
614trying hard on making that true, but you never know. 974trying hard on making that true, but you never know.
615 975
616Second, you need to avoid resource-starving attacks. That means you should 976Second, you need to avoid resource-starving attacks. That means you should
617limit the size of JSON texts you accept, or make sure then when your 977limit the size of JSON texts you accept, or make sure then when your
618resources run out, thats just fine (e.g. by using a separate process that 978resources run out, that's just fine (e.g. by using a separate process that
619can crash safely). The size of a JSON text in octets or characters is 979can crash safely). The size of a JSON text in octets or characters is
620usually a good indication of the size of the resources required to decode 980usually a good indication of the size of the resources required to decode
621it into a Perl structure. 981it into a Perl structure. While JSON::XS can check the size of the JSON
982text, it might be too late when you already have it in memory, so you
983might want to check the size before you accept the string.
622 984
623Third, JSON::XS recurses using the C stack when decoding objects and 985Third, JSON::XS recurses using the C stack when decoding objects and
624arrays. The C stack is a limited resource: for instance, on my amd64 986arrays. The C stack is a limited resource: for instance, on my amd64
625machine with 8MB of stack size I can decode around 180k nested arrays 987machine with 8MB of stack size I can decode around 180k nested arrays but
626but only 14k nested JSON objects. If that is exceeded, the program 988only 14k nested JSON objects (due to perl itself recursing deeply on croak
989to free the temporary). If that is exceeded, the program crashes. to be
627crashes. Thats why the default nesting limit is set to 8192. If your 990conservative, the default nesting limit is set to 512. If your process
628process has a smaller stack, you should adjust this setting accordingly 991has a smaller stack, you should adjust this setting accordingly with the
629with the C<max_depth> method. 992C<max_depth> method.
630 993
631And last but least, something else could bomb you that I forgot to think 994And last but least, something else could bomb you that I forgot to think
632of. In that case, you get to keep the pieces. I am alway sopen for hints, 995of. In that case, you get to keep the pieces. I am always open for hints,
633though... 996though...
997
998If you are using JSON::XS to return packets to consumption
999by JavaScript scripts in a browser you should have a look at
1000L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
1001you are vulnerable to some common attack vectors (which really are browser
1002design bugs, but it is still you who will have to deal with it, as major
1003browser developers care only for features, not about doing security
1004right).
1005
1006
1007=head1 THREADS
1008
1009This module is I<not> guaranteed to be thread safe and there are no
1010plans to change this until Perl gets thread support (as opposed to the
1011horribly slow so-called "threads" which are simply slow and bloated
1012process simulations - use fork, its I<much> faster, cheaper, better).
1013
1014(It might actually work, but you have been warned).
634 1015
635 1016
636=head1 BUGS 1017=head1 BUGS
637 1018
638While the goal of this module is to be correct, that unfortunately does 1019While the goal of this module is to be correct, that unfortunately does
639not mean its bug-free, only that I think its design is bug-free. It is 1020not mean its bug-free, only that I think its design is bug-free. It is
640still relatively early in its development. If you keep reporting bugs they 1021still relatively early in its development. If you keep reporting bugs they
641will be fixed swiftly, though. 1022will be fixed swiftly, though.
642 1023
1024Please refrain from using rt.cpan.org or any other bug reporting
1025service. I put the contact address into my modules for a reason.
1026
643=cut 1027=cut
1028
1029our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
1030our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
1031
1032sub true() { $true }
1033sub false() { $false }
1034
1035sub is_bool($) {
1036 UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
1037# or UNIVERSAL::isa $_[0], "JSON::Literal"
1038}
1039
1040XSLoader::load "JSON::XS", $VERSION;
1041
1042package JSON::XS::Boolean;
1043
1044use overload
1045 "0+" => sub { ${$_[0]} },
1046 "++" => sub { $_[0] = ${$_[0]} + 1 },
1047 "--" => sub { $_[0] = ${$_[0]} - 1 },
1048 fallback => 1;
644 1049
6451; 10501;
646 1051
647=head1 AUTHOR 1052=head1 AUTHOR
648 1053

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