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Revision 1.20 by root, Sun Mar 25 00:47:42 2007 UTC vs.
Revision 1.70 by root, Tue Nov 13 22:59:08 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 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)
7
5=head1 SYNOPSIS 8=head1 SYNOPSIS
6 9
7 use JSON::XS; 10 use JSON::XS;
8 11
9 # exported functions, croak on error 12 # exported functions, they croak on error
13 # and expect/generate UTF-8
10 14
11 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 15 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
12 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 16 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text;
13 17
14 # oo-interface 18 # OO-interface
15 19
16 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 20 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
17 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 21 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
18 $perl_scalar = $coder->decode ($unicode_json_text); 22 $perl_scalar = $coder->decode ($unicode_json_text);
19 23
36 40
37=head2 FEATURES 41=head2 FEATURES
38 42
39=over 4 43=over 4
40 44
41=item * correct handling of unicode issues 45=item * correct Unicode handling
42 46
43This 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
44it does so. 48it does so.
45 49
46=item * round-trip integrity 50=item * round-trip integrity
47 51
48When you serialise a perl data structure using only datatypes supported 52When you serialise a perl data structure using only datatypes supported
49by JSON, the deserialised data structure is identical on the Perl level. 53by JSON, the deserialised data structure is identical on the Perl level.
50(e.g. the string "2.0" doesn't suddenly become "2"). 54(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
55like a number).
51 56
52=item * strict checking of JSON correctness 57=item * strict checking of JSON correctness
53 58
54There is no guessing, no generating of illegal JSON texts by default, 59There is no guessing, no generating of illegal JSON texts by default,
55and only JSON is accepted as input by default (the latter is a security 60and only JSON is accepted as input by default (the latter is a security
65This 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
66interface. 71interface.
67 72
68=item * reasonably versatile output formats 73=item * reasonably versatile output formats
69 74
70You can choose between the most compact guarenteed single-line format 75You can choose between the most compact guaranteed single-line format
71possible (nice for simple line-based protocols), a pure-ascii format (for 76possible (nice for simple line-based protocols), a pure-ascii format
72when your transport is not 8-bit clean), or a pretty-printed format (for 77(for when your transport is not 8-bit clean, still supports the whole
73when you want to read that stuff). Or you can combine those features in 78Unicode range), or a pretty-printed format (for when you want to read that
74whatever way you like. 79stuff). Or you can combine those features in whatever way you like.
75 80
76=back 81=back
77 82
78=cut 83=cut
79 84
80package JSON::XS; 85package JSON::XS;
81 86
82use strict; 87use strict;
83 88
84BEGIN {
85 our $VERSION = '0.7'; 89our $VERSION = '1.53';
86 our @ISA = qw(Exporter); 90our @ISA = qw(Exporter);
87 91
88 our @EXPORT = qw(to_json from_json); 92our @EXPORT = qw(to_json from_json);
89 require Exporter;
90 93
91 require XSLoader; 94use Exporter;
92 XSLoader::load JSON::XS::, $VERSION; 95use XSLoader;
93}
94 96
95=head1 FUNCTIONAL INTERFACE 97=head1 FUNCTIONAL INTERFACE
96 98
97The following convinience methods are provided by this module. They are 99The following convenience methods are provided by this module. They are
98exported by default: 100exported by default:
99 101
100=over 4 102=over 4
101 103
102=item $json_text = to_json $perl_scalar 104=item $json_text = to_json $perl_scalar
103 105
104Converts 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
105a 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.
106octets only). Croaks on error.
107 108
108This function call is functionally identical to: 109This function call is functionally identical to:
109 110
110 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 111 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
111 112
112except being faster. 113except being faster.
113 114
114=item $perl_scalar = from_json $json_text 115=item $perl_scalar = from_json $json_text
115 116
116The 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
117parse 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
118scalar or reference. Croaks on error. 119reference. Croaks on error.
119 120
120This function call is functionally identical to: 121This function call is functionally identical to:
121 122
122 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 123 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
123 124
124except being faster. 125except being faster.
125 126
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
126=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 :)
185
127 186
128=head1 OBJECT-ORIENTED INTERFACE 187=head1 OBJECT-ORIENTED INTERFACE
129 188
130The object oriented interface lets you configure your own encoding or 189The object oriented interface lets you configure your own encoding or
131decoding style, within the limits of supported formats. 190decoding style, within the limits of supported formats.
145 204
146=item $json = $json->ascii ([$enable]) 205=item $json = $json->ascii ([$enable])
147 206
148If C<$enable> is true (or missing), then the C<encode> method will not 207If C<$enable> is true (or missing), then the C<encode> method will not
149generate characters outside the code range C<0..127> (which is ASCII). Any 208generate characters outside the code range C<0..127> (which is ASCII). Any
150unicode characters outside that range will be escaped using either a 209Unicode characters outside that range will be escaped using either a
151single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, 210single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
152as per RFC4627. 211as per RFC4627. The resulting encoded JSON text can be treated as a native
212Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
213or any other superset of ASCII.
153 214
154If C<$enable> is false, then the C<encode> method will not escape Unicode 215If C<$enable> is false, then the C<encode> method will not escape Unicode
155characters unless required by the JSON syntax. This results in a faster 216characters unless required by the JSON syntax or other flags. This results
156and more compact format. 217in a faster and more compact format.
218
219The main use for this flag is to produce JSON texts that can be
220transmitted over a 7-bit channel, as the encoded JSON texts will not
221contain any 8 bit characters.
157 222
158 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 223 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
159 => ["\ud801\udc01"] 224 => ["\ud801\udc01"]
225
226=item $json = $json->latin1 ([$enable])
227
228If C<$enable> is true (or missing), then the C<encode> method will encode
229the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
230outside the code range C<0..255>. The resulting string can be treated as a
231latin1-encoded JSON text or a native Unicode string. The C<decode> method
232will not be affected in any way by this flag, as C<decode> by default
233expects Unicode, which is a strict superset of latin1.
234
235If C<$enable> is false, then the C<encode> method will not escape Unicode
236characters unless required by the JSON syntax or other flags.
237
238The main use for this flag is efficiently encoding binary data as JSON
239text, as most octets will not be escaped, resulting in a smaller encoded
240size. The disadvantage is that the resulting JSON text is encoded
241in latin1 (and must correctly be treated as such when storing and
242transferring), a rare encoding for JSON. It is therefore most useful when
243you want to store data structures known to contain binary data efficiently
244in files or databases, not when talking to other JSON encoders/decoders.
245
246 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
247 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
160 248
161=item $json = $json->utf8 ([$enable]) 249=item $json = $json->utf8 ([$enable])
162 250
163If C<$enable> is true (or missing), then the C<encode> method will encode 251If C<$enable> is true (or missing), then the C<encode> method will encode
164the JSON result into UTF-8, as required by many protocols, while the 252the JSON result into UTF-8, as required by many protocols, while the
167range C<0..255>, they are thus useful for bytewise/binary I/O. In future 255range C<0..255>, they are thus useful for bytewise/binary I/O. In future
168versions, enabling this option might enable autodetection of the UTF-16 256versions, enabling this option might enable autodetection of the UTF-16
169and UTF-32 encoding families, as described in RFC4627. 257and UTF-32 encoding families, as described in RFC4627.
170 258
171If C<$enable> is false, then the C<encode> method will return the JSON 259If C<$enable> is false, then the C<encode> method will return the JSON
172string as a (non-encoded) unicode string, while C<decode> expects thus a 260string as a (non-encoded) Unicode string, while C<decode> expects thus a
173unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs 261Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
174to be done yourself, e.g. using the Encode module. 262to be done yourself, e.g. using the Encode module.
175 263
176Example, output UTF-16BE-encoded JSON: 264Example, output UTF-16BE-encoded JSON:
177 265
178 use Encode; 266 use Encode;
202 290
203=item $json = $json->indent ([$enable]) 291=item $json = $json->indent ([$enable])
204 292
205If C<$enable> is true (or missing), then the C<encode> method will use a multiline 293If C<$enable> is true (or missing), then the C<encode> method will use a multiline
206format as output, putting every array member or object/hash key-value pair 294format as output, putting every array member or object/hash key-value pair
207into its own line, identing them properly. 295into its own line, indenting them properly.
208 296
209If C<$enable> is false, no newlines or indenting will be produced, and the 297If C<$enable> is false, no newlines or indenting will be produced, and the
210resulting JSON text is guarenteed not to contain any C<newlines>. 298resulting JSON text is guaranteed not to contain any C<newlines>.
211 299
212This setting has no effect when decoding JSON texts. 300This setting has no effect when decoding JSON texts.
213 301
214=item $json = $json->space_before ([$enable]) 302=item $json = $json->space_before ([$enable])
215 303
240 328
241Example, space_before and indent disabled, space_after enabled: 329Example, space_before and indent disabled, space_after enabled:
242 330
243 {"key": "value"} 331 {"key": "value"}
244 332
333=item $json = $json->relaxed ([$enable])
334
335If C<$enable> is true (or missing), then C<decode> will accept some
336extensions to normal JSON syntax (see below). C<encode> will not be
337affected in anyway. I<Be aware that this option makes you accept invalid
338JSON texts as if they were valid!>. I suggest only to use this option to
339parse application-specific files written by humans (configuration files,
340resource files etc.)
341
342If C<$enable> is false (the default), then C<decode> will only accept
343valid JSON texts.
344
345Currently accepted extensions are:
346
347=over 4
348
349=item * list items can have an end-comma
350
351JSON I<separates> array elements and key-value pairs with commas. This
352can be annoying if you write JSON texts manually and want to be able to
353quickly append elements, so this extension accepts comma at the end of
354such items not just between them:
355
356 [
357 1,
358 2, <- this comma not normally allowed
359 ]
360 {
361 "k1": "v1",
362 "k2": "v2", <- this comma not normally allowed
363 }
364
365=item * shell-style '#'-comments
366
367Whenever JSON allows whitespace, shell-style comments are additionally
368allowed. They are terminated by the first carriage-return or line-feed
369character, after which more white-space and comments are allowed.
370
371 [
372 1, # this comment not allowed in JSON
373 # neither this one...
374 ]
375
376=back
377
245=item $json = $json->canonical ([$enable]) 378=item $json = $json->canonical ([$enable])
246 379
247If C<$enable> is true (or missing), then the C<encode> method will output JSON objects 380If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
248by sorting their keys. This is adding a comparatively high overhead. 381by sorting their keys. This is adding a comparatively high overhead.
249 382
251pairs in the order Perl stores them (which will likely change between runs 384pairs in the order Perl stores them (which will likely change between runs
252of the same script). 385of the same script).
253 386
254This option is useful if you want the same data structure to be encoded as 387This option is useful if you want the same data structure to be encoded as
255the same JSON text (given the same overall settings). If it is disabled, 388the same JSON text (given the same overall settings). If it is disabled,
256the same hash migh be encoded differently even if contains the same data, 389the same hash might be encoded differently even if contains the same data,
257as key-value pairs have no inherent ordering in Perl. 390as key-value pairs have no inherent ordering in Perl.
258 391
259This setting has no effect when decoding JSON texts. 392This setting has no effect when decoding JSON texts.
260 393
261=item $json = $json->allow_nonref ([$enable]) 394=item $json = $json->allow_nonref ([$enable])
274resulting in an invalid JSON text: 407resulting in an invalid JSON text:
275 408
276 JSON::XS->new->allow_nonref->encode ("Hello, World!") 409 JSON::XS->new->allow_nonref->encode ("Hello, World!")
277 => "Hello, World!" 410 => "Hello, World!"
278 411
412=item $json = $json->allow_blessed ([$enable])
413
414If C<$enable> is true (or missing), then the C<encode> method will not
415barf when it encounters a blessed reference. Instead, the value of the
416B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
417disabled or no C<to_json> method found) or a representation of the
418object (C<convert_blessed> enabled and C<to_json> method found) is being
419encoded. Has no effect on C<decode>.
420
421If C<$enable> is false (the default), then C<encode> will throw an
422exception when it encounters a blessed object.
423
424=item $json = $json->convert_blessed ([$enable])
425
426If C<$enable> is true (or missing), then C<encode>, upon encountering a
427blessed object, will check for the availability of the C<TO_JSON> method
428on the object's class. If found, it will be called in scalar context
429and the resulting scalar will be encoded instead of the object. If no
430C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
431to do.
432
433The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
434returns other blessed objects, those will be handled in the same
435way. C<TO_JSON> must take care of not causing an endless recursion cycle
436(== crash) in this case. The name of C<TO_JSON> was chosen because other
437methods called by the Perl core (== not by the user of the object) are
438usually in upper case letters and to avoid collisions with the C<to_json>
439function.
440
441This setting does not yet influence C<decode> in any way, but in the
442future, global hooks might get installed that influence C<decode> and are
443enabled by this setting.
444
445If C<$enable> is false, then the C<allow_blessed> setting will decide what
446to do when a blessed object is found.
447
448=item $json = $json->filter_json_object ([$coderef->($hashref)])
449
450When C<$coderef> is specified, it will be called from C<decode> each
451time it decodes a JSON object. The only argument is a reference to the
452newly-created hash. If the code references returns a single scalar (which
453need not be a reference), this value (i.e. a copy of that scalar to avoid
454aliasing) is inserted into the deserialised data structure. If it returns
455an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
456original deserialised hash will be inserted. This setting can slow down
457decoding considerably.
458
459When C<$coderef> is omitted or undefined, any existing callback will
460be removed and C<decode> will not change the deserialised hash in any
461way.
462
463Example, convert all JSON objects into the integer 5:
464
465 my $js = JSON::XS->new->filter_json_object (sub { 5 });
466 # returns [5]
467 $js->decode ('[{}]')
468 # throw an exception because allow_nonref is not enabled
469 # so a lone 5 is not allowed.
470 $js->decode ('{"a":1, "b":2}');
471
472=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
473
474Works remotely similar to C<filter_json_object>, but is only called for
475JSON objects having a single key named C<$key>.
476
477This C<$coderef> is called before the one specified via
478C<filter_json_object>, if any. It gets passed the single value in the JSON
479object. If it returns a single value, it will be inserted into the data
480structure. If it returns nothing (not even C<undef> but the empty list),
481the callback from C<filter_json_object> will be called next, as if no
482single-key callback were specified.
483
484If C<$coderef> is omitted or undefined, the corresponding callback will be
485disabled. There can only ever be one callback for a given key.
486
487As this callback gets called less often then the C<filter_json_object>
488one, decoding speed will not usually suffer as much. Therefore, single-key
489objects make excellent targets to serialise Perl objects into, especially
490as single-key JSON objects are as close to the type-tagged value concept
491as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
492support this in any way, so you need to make sure your data never looks
493like a serialised Perl hash.
494
495Typical names for the single object key are C<__class_whatever__>, or
496C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
497things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
498with real hashes.
499
500Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
501into the corresponding C<< $WIDGET{<id>} >> object:
502
503 # return whatever is in $WIDGET{5}:
504 JSON::XS
505 ->new
506 ->filter_json_single_key_object (__widget__ => sub {
507 $WIDGET{ $_[0] }
508 })
509 ->decode ('{"__widget__": 5')
510
511 # this can be used with a TO_JSON method in some "widget" class
512 # for serialisation to json:
513 sub WidgetBase::TO_JSON {
514 my ($self) = @_;
515
516 unless ($self->{id}) {
517 $self->{id} = ..get..some..id..;
518 $WIDGET{$self->{id}} = $self;
519 }
520
521 { __widget__ => $self->{id} }
522 }
523
279=item $json = $json->shrink ([$enable]) 524=item $json = $json->shrink ([$enable])
280 525
281Perl usually over-allocates memory a bit when allocating space for 526Perl usually over-allocates memory a bit when allocating space for
282strings. This flag optionally resizes strings generated by either 527strings. This flag optionally resizes strings generated by either
283C<encode> or C<decode> to their minimum size possible. This can save 528C<encode> or C<decode> to their minimum size possible. This can save
284memory when your JSON texts are either very very long or you have many 529memory when your JSON texts are either very very long or you have many
285short strings. It will also try to downgrade any strings to octet-form 530short strings. It will also try to downgrade any strings to octet-form
286if possible: perl stores strings internally either in an encoding called 531if possible: perl stores strings internally either in an encoding called
287UTF-X or in octet-form. The latter cannot store everything but uses less 532UTF-X or in octet-form. The latter cannot store everything but uses less
288space in general. 533space in general (and some buggy Perl or C code might even rely on that
534internal representation being used).
289 535
536The actual definition of what shrink does might change in future versions,
537but it will always try to save space at the expense of time.
538
290If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit, 539If C<$enable> is true (or missing), the string returned by C<encode> will
291while all strings generated by C<decode> will also be shrunk-to-fit. 540be shrunk-to-fit, while all strings generated by C<decode> will also be
541shrunk-to-fit.
292 542
293If C<$enable> is false, then the normal perl allocation algorithms are used. 543If C<$enable> is false, then the normal perl allocation algorithms are used.
294If you work with your data, then this is likely to be faster. 544If you work with your data, then this is likely to be faster.
295 545
296In the future, this setting might control other things, such as converting 546In the future, this setting might control other things, such as converting
297strings that look like integers or floats into integers or floats 547strings that look like integers or floats into integers or floats
298internally (there is no difference on the Perl level), saving space. 548internally (there is no difference on the Perl level), saving space.
549
550=item $json = $json->max_depth ([$maximum_nesting_depth])
551
552Sets the maximum nesting level (default C<512>) accepted while encoding
553or decoding. If the JSON text or Perl data structure has an equal or
554higher nesting level then this limit, then the encoder and decoder will
555stop and croak at that point.
556
557Nesting level is defined by number of hash- or arrayrefs that the encoder
558needs to traverse to reach a given point or the number of C<{> or C<[>
559characters without their matching closing parenthesis crossed to reach a
560given character in a string.
561
562Setting the maximum depth to one disallows any nesting, so that ensures
563that the object is only a single hash/object or array.
564
565The argument to C<max_depth> will be rounded up to the next highest power
566of two. If no argument is given, the highest possible setting will be
567used, which is rarely useful.
568
569See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
570
571=item $json = $json->max_size ([$maximum_string_size])
572
573Set the maximum length a JSON text may have (in bytes) where decoding is
574being attempted. The default is C<0>, meaning no limit. When C<decode>
575is called on a string longer then this number of characters it will not
576attempt to decode the string but throw an exception. This setting has no
577effect on C<encode> (yet).
578
579The argument to C<max_size> will be rounded up to the next B<highest>
580power of two (so may be more than requested). If no argument is given, the
581limit check will be deactivated (same as when C<0> is specified).
582
583See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
299 584
300=item $json_text = $json->encode ($perl_scalar) 585=item $json_text = $json->encode ($perl_scalar)
301 586
302Converts the given Perl data structure (a simple scalar or a reference 587Converts the given Perl data structure (a simple scalar or a reference
303to a hash or array) to its JSON representation. Simple scalars will be 588to a hash or array) to its JSON representation. Simple scalars will be
313 598
314JSON numbers and strings become simple Perl scalars. JSON arrays become 599JSON numbers and strings become simple Perl scalars. JSON arrays become
315Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes 600Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
316C<1>, C<false> becomes C<0> and C<null> becomes C<undef>. 601C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
317 602
603=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
604
605This works like the C<decode> method, but instead of raising an exception
606when there is trailing garbage after the first JSON object, it will
607silently stop parsing there and return the number of characters consumed
608so far.
609
610This is useful if your JSON texts are not delimited by an outer protocol
611(which is not the brightest thing to do in the first place) and you need
612to know where the JSON text ends.
613
614 JSON::XS->new->decode_prefix ("[1] the tail")
615 => ([], 3)
616
318=back 617=back
618
319 619
320=head1 MAPPING 620=head1 MAPPING
321 621
322This section describes how JSON::XS maps Perl values to JSON values and 622This section describes how JSON::XS maps Perl values to JSON values and
323vice versa. These mappings are designed to "do the right thing" in most 623vice versa. These mappings are designed to "do the right thing" in most
324circumstances automatically, preserving round-tripping characteristics 624circumstances automatically, preserving round-tripping characteristics
325(what you put in comes out as something equivalent). 625(what you put in comes out as something equivalent).
326 626
327For the more enlightened: note that in the following descriptions, 627For the more enlightened: note that in the following descriptions,
328lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl> 628lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
329refers to the abstract Perl language itself. 629refers to the abstract Perl language itself.
330 630
631
331=head2 JSON -> PERL 632=head2 JSON -> PERL
332 633
333=over 4 634=over 4
334 635
335=item object 636=item object
336 637
337A JSON object becomes a reference to a hash in Perl. No ordering of object 638A JSON object becomes a reference to a hash in Perl. No ordering of object
338keys is preserved (JSON does not preserver object key ordering itself). 639keys is preserved (JSON does not preserve object key ordering itself).
339 640
340=item array 641=item array
341 642
342A JSON array becomes a reference to an array in Perl. 643A JSON array becomes a reference to an array in Perl.
343 644
347are represented by the same codepoints in the Perl string, so no manual 648are represented by the same codepoints in the Perl string, so no manual
348decoding is necessary. 649decoding is necessary.
349 650
350=item number 651=item number
351 652
352A JSON number becomes either an integer or numeric (floating point) 653A JSON number becomes either an integer, numeric (floating point) or
353scalar in perl, depending on its range and any fractional parts. On the 654string scalar in perl, depending on its range and any fractional parts. On
354Perl level, there is no difference between those as Perl handles all the 655the Perl level, there is no difference between those as Perl handles all
355conversion details, but an integer may take slightly less memory and might 656the conversion details, but an integer may take slightly less memory and
356represent more values exactly than (floating point) numbers. 657might represent more values exactly than (floating point) numbers.
658
659If the number consists of digits only, JSON::XS will try to represent
660it as an integer value. If that fails, it will try to represent it as
661a numeric (floating point) value if that is possible without loss of
662precision. Otherwise it will preserve the number as a string value.
663
664Numbers containing a fractional or exponential part will always be
665represented as numeric (floating point) values, possibly at a loss of
666precision.
667
668This might create round-tripping problems as numbers might become strings,
669but as Perl is typeless there is no other way to do it.
357 670
358=item true, false 671=item true, false
359 672
360These JSON atoms become C<0>, C<1>, respectively. Information is lost in 673These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
361this process. Future versions might represent those values differently, 674respectively. They are overloaded to act almost exactly like the numbers
362but they will be guarenteed to act like these integers would normally in 675C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
363Perl. 676the C<JSON::XS::is_bool> function.
364 677
365=item null 678=item null
366 679
367A JSON null atom becomes C<undef> in Perl. 680A JSON null atom becomes C<undef> in Perl.
368 681
369=back 682=back
683
370 684
371=head2 PERL -> JSON 685=head2 PERL -> JSON
372 686
373The mapping from Perl to JSON is slightly more difficult, as Perl is a 687The mapping from Perl to JSON is slightly more difficult, as Perl is a
374truly typeless language, so we can only guess which JSON type is meant by 688truly typeless language, so we can only guess which JSON type is meant by
377=over 4 691=over 4
378 692
379=item hash references 693=item hash references
380 694
381Perl hash references become JSON objects. As there is no inherent ordering 695Perl hash references become JSON objects. As there is no inherent ordering
382in hash keys, they will usually be encoded in a pseudo-random order that 696in hash keys (or JSON objects), they will usually be encoded in a
383can change between runs of the same program but stays generally the same 697pseudo-random order that can change between runs of the same program but
384within a single run of a program. JSON::XS can optionally sort the hash 698stays generally the same within a single run of a program. JSON::XS can
385keys (determined by the I<canonical> flag), so the same datastructure 699optionally sort the hash keys (determined by the I<canonical> flag), so
386will serialise to the same JSON text (given same settings and version of 700the same datastructure will serialise to the same JSON text (given same
387JSON::XS), but this incurs a runtime overhead. 701settings and version of JSON::XS), but this incurs a runtime overhead
702and is only rarely useful, e.g. when you want to compare some JSON text
703against another for equality.
388 704
389=item array references 705=item array references
390 706
391Perl array references become JSON arrays. 707Perl array references become JSON arrays.
708
709=item other references
710
711Other unblessed references are generally not allowed and will cause an
712exception to be thrown, except for references to the integers C<0> and
713C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
714also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
715
716 to_json [\0,JSON::XS::true] # yields [false,true]
717
718=item JSON::XS::true, JSON::XS::false
719
720These special values become JSON true and JSON false values,
721respectively. You can also use C<\1> and C<\0> directly if you want.
392 722
393=item blessed objects 723=item blessed objects
394 724
395Blessed objects are not allowed. JSON::XS currently tries to encode their 725Blessed objects are not allowed. JSON::XS currently tries to encode their
396underlying representation (hash- or arrayref), but this behaviour might 726underlying representation (hash- or arrayref), but this behaviour might
413 to_json [$value] # yields ["5"] 743 to_json [$value] # yields ["5"]
414 744
415 # undef becomes null 745 # undef becomes null
416 to_json [undef] # yields [null] 746 to_json [undef] # yields [null]
417 747
418You can force the type to be a string by stringifying it: 748You can force the type to be a JSON string by stringifying it:
419 749
420 my $x = 3.1; # some variable containing a number 750 my $x = 3.1; # some variable containing a number
421 "$x"; # stringified 751 "$x"; # stringified
422 $x .= ""; # another, more awkward way to stringify 752 $x .= ""; # another, more awkward way to stringify
423 print $x; # perl does it for you, too, quite often 753 print $x; # perl does it for you, too, quite often
424 754
425You can force the type to be a number by numifying it: 755You can force the type to be a JSON number by numifying it:
426 756
427 my $x = "3"; # some variable containing a string 757 my $x = "3"; # some variable containing a string
428 $x += 0; # numify it, ensuring it will be dumped as a number 758 $x += 0; # numify it, ensuring it will be dumped as a number
429 $x *= 1; # same thing, the choise is yours. 759 $x *= 1; # same thing, the choice is yours.
430 760
431You can not currently output JSON booleans or force the type in other, 761You can not currently force the type in other, less obscure, ways. Tell me
432less obscure, ways. Tell me if you need this capability. 762if you need this capability.
433
434=item circular data structures
435
436Those will be encoded until memory or stackspace runs out.
437 763
438=back 764=back
765
439 766
440=head1 COMPARISON 767=head1 COMPARISON
441 768
442As already mentioned, this module was created because none of the existing 769As already mentioned, this module was created because none of the existing
443JSON modules could be made to work correctly. First I will describe the 770JSON modules could be made to work correctly. First I will describe the
449 776
450=item JSON 1.07 777=item JSON 1.07
451 778
452Slow (but very portable, as it is written in pure Perl). 779Slow (but very portable, as it is written in pure Perl).
453 780
454Undocumented/buggy Unicode handling (how JSON handles unicode values is 781Undocumented/buggy Unicode handling (how JSON handles Unicode values is
455undocumented. One can get far by feeding it unicode strings and doing 782undocumented. One can get far by feeding it Unicode strings and doing
456en-/decoding oneself, but unicode escapes are not working properly). 783en-/decoding oneself, but Unicode escapes are not working properly).
457 784
458No roundtripping (strings get clobbered if they look like numbers, e.g. 785No round-tripping (strings get clobbered if they look like numbers, e.g.
459the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will 786the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
460decode into the number 2. 787decode into the number 2.
461 788
462=item JSON::PC 0.01 789=item JSON::PC 0.01
463 790
464Very fast. 791Very fast.
465 792
466Undocumented/buggy Unicode handling. 793Undocumented/buggy Unicode handling.
467 794
468No roundtripping. 795No round-tripping.
469 796
470Has problems handling many Perl values (e.g. regex results and other magic 797Has problems handling many Perl values (e.g. regex results and other magic
471values will make it croak). 798values will make it croak).
472 799
473Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> 800Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
483Very inflexible (no human-readable format supported, format pretty much 810Very inflexible (no human-readable format supported, format pretty much
484undocumented. I need at least a format for easy reading by humans and a 811undocumented. I need at least a format for easy reading by humans and a
485single-line compact format for use in a protocol, and preferably a way to 812single-line compact format for use in a protocol, and preferably a way to
486generate ASCII-only JSON texts). 813generate ASCII-only JSON texts).
487 814
488Completely broken (and confusingly documented) Unicode handling (unicode 815Completely broken (and confusingly documented) Unicode handling (Unicode
489escapes are not working properly, you need to set ImplicitUnicode to 816escapes are not working properly, you need to set ImplicitUnicode to
490I<different> values on en- and decoding to get symmetric behaviour). 817I<different> values on en- and decoding to get symmetric behaviour).
491 818
492No roundtripping (simple cases work, but this depends on wether the scalar 819No round-tripping (simple cases work, but this depends on whether the scalar
493value was used in a numeric context or not). 820value was used in a numeric context or not).
494 821
495Dumping hashes may skip hash values depending on iterator state. 822Dumping hashes may skip hash values depending on iterator state.
496 823
497Unmaintained (maintainer unresponsive for many months, bugs are not 824Unmaintained (maintainer unresponsive for many months, bugs are not
498getting fixed). 825getting fixed).
499 826
500Does not check input for validity (i.e. will accept non-JSON input and 827Does not check input for validity (i.e. will accept non-JSON input and
501return "something" instead of raising an exception. This is a security 828return "something" instead of raising an exception. This is a security
502issue: imagine two banks transfering money between each other using 829issue: imagine two banks transferring money between each other using
503JSON. One bank might parse a given non-JSON request and deduct money, 830JSON. One bank might parse a given non-JSON request and deduct money,
504while the other might reject the transaction with a syntax error. While a 831while the other might reject the transaction with a syntax error. While a
505good protocol will at least recover, that is extra unnecessary work and 832good protocol will at least recover, that is extra unnecessary work and
506the transaction will still not succeed). 833the transaction will still not succeed).
507 834
508=item JSON::DWIW 0.04 835=item JSON::DWIW 0.04
509 836
510Very fast. Very natural. Very nice. 837Very fast. Very natural. Very nice.
511 838
512Undocumented unicode handling (but the best of the pack. Unicode escapes 839Undocumented Unicode handling (but the best of the pack. Unicode escapes
513still don't get parsed properly). 840still don't get parsed properly).
514 841
515Very inflexible. 842Very inflexible.
516 843
517No roundtripping. 844No round-tripping.
518 845
519Does not generate valid JSON texts (key strings are often unquoted, empty keys 846Does not generate valid JSON texts (key strings are often unquoted, empty keys
520result in nothing being output) 847result in nothing being output)
521 848
522Does not check input for validity. 849Does not check input for validity.
523 850
524=back 851=back
852
853
854=head2 JSON and YAML
855
856You often hear that JSON is a subset (or a close subset) of YAML. This is,
857however, a mass hysteria and very far from the truth. In general, there is
858no way to configure JSON::XS to output a data structure as valid YAML.
859
860If you really must use JSON::XS to generate YAML, you should use this
861algorithm (subject to change in future versions):
862
863 my $to_yaml = JSON::XS->new->utf8->space_after (1);
864 my $yaml = $to_yaml->encode ($ref) . "\n";
865
866This will usually generate JSON texts that also parse as valid
867YAML. Please note that YAML has hardcoded limits on (simple) object key
868lengths that JSON doesn't have, so you should make sure that your hash
869keys are noticeably shorter than the 1024 characters YAML allows.
870
871There might be other incompatibilities that I am not aware of. In general
872you should not try to generate YAML with a JSON generator or vice versa,
873or try to parse JSON with a YAML parser or vice versa: chances are high
874that you will run into severe interoperability problems.
875
525 876
526=head2 SPEED 877=head2 SPEED
527 878
528It seems that JSON::XS is surprisingly fast, as shown in the following 879It seems that JSON::XS is surprisingly fast, as shown in the following
529tables. They have been generated with the help of the C<eg/bench> program 880tables. They have been generated with the help of the C<eg/bench> program
530in the JSON::XS distribution, to make it easy to compare on your own 881in the JSON::XS distribution, to make it easy to compare on your own
531system. 882system.
532 883
533First comes a comparison between various modules using a very short JSON 884First comes a comparison between various modules using a very short
534string: 885single-line JSON string:
535 886
536 {"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null} 887 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
888 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
537 889
538It shows the number of encodes/decodes per second (JSON::XS uses the 890It shows the number of encodes/decodes per second (JSON::XS uses
539functional interface, while JSON::XS/2 uses the OO interface with 891the functional interface, while JSON::XS/2 uses the OO interface
540pretty-printing and hashkey sorting enabled). Higher is better: 892with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
893shrink). Higher is better:
541 894
895 Storable | 15779.925 | 14169.946 |
896 -----------+------------+------------+
542 module | encode | decode | 897 module | encode | decode |
543 -----------|------------|------------| 898 -----------|------------|------------|
544 JSON | 11488.516 | 7823.035 | 899 JSON | 4990.842 | 4088.813 |
545 JSON::DWIW | 94708.054 | 129094.260 | 900 JSON::DWIW | 51653.990 | 71575.154 |
546 JSON::PC | 63884.157 | 128528.212 | 901 JSON::PC | 65948.176 | 74631.744 |
547 JSON::Syck | 34898.677 | 42096.911 | 902 JSON::PP | 8931.652 | 3817.168 |
548 JSON::XS | 654027.064 | 396423.669 | 903 JSON::Syck | 24877.248 | 27776.848 |
549 JSON::XS/2 | 371564.190 | 371725.613 | 904 JSON::XS | 388361.481 | 227951.304 |
905 JSON::XS/2 | 227951.304 | 218453.333 |
906 JSON::XS/3 | 338250.323 | 218453.333 |
907 Storable | 16500.016 | 135300.129 |
550 -----------+------------+------------+ 908 -----------+------------+------------+
551 909
552That is, JSON::XS is more than six times faster than JSON::DWIW on 910That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
553encoding, more than three times faster on decoding, and about thirty times 911about three times faster on decoding, and over forty times faster
554faster than JSON, even with pretty-printing and key sorting. 912than JSON, even with pretty-printing and key sorting. It also compares
913favourably to Storable for small amounts of data.
555 914
556Using a longer test string (roughly 18KB, generated from Yahoo! Locals 915Using a longer test string (roughly 18KB, generated from Yahoo! Locals
557search API (http://nanoref.com/yahooapis/mgPdGg): 916search API (http://nanoref.com/yahooapis/mgPdGg):
558 917
559 module | encode | decode | 918 module | encode | decode |
560 -----------|------------|------------| 919 -----------|------------|------------|
561 JSON | 273.023 | 44.674 | 920 JSON | 55.260 | 34.971 |
562 JSON::DWIW | 1089.383 | 1145.704 | 921 JSON::DWIW | 825.228 | 1082.513 |
563 JSON::PC | 3097.419 | 2393.921 | 922 JSON::PC | 3571.444 | 2394.829 |
564 JSON::Syck | 514.060 | 843.053 | 923 JSON::PP | 210.987 | 32.574 |
565 JSON::XS | 6479.668 | 3636.364 | 924 JSON::Syck | 552.551 | 787.544 |
566 JSON::XS/2 | 3774.221 | 3599.124 | 925 JSON::XS | 5780.463 | 4854.519 |
926 JSON::XS/2 | 3869.998 | 4798.975 |
927 JSON::XS/3 | 5862.880 | 4798.975 |
928 Storable | 4445.002 | 5235.027 |
567 -----------+------------+------------+ 929 -----------+------------+------------+
568 930
569Again, JSON::XS leads by far. 931Again, JSON::XS leads by far (except for Storable which non-surprisingly
932decodes faster).
570 933
571On large strings containing lots of high unicode characters, some modules 934On large strings containing lots of high Unicode characters, some modules
572(such as JSON::PC) seem to decode faster than JSON::XS, but the result 935(such as JSON::PC) seem to decode faster than JSON::XS, but the result
573will be broken due to missing (or wrong) unicode handling. Others refuse 936will be broken due to missing (or wrong) Unicode handling. Others refuse
574to decode or encode properly, so it was impossible to prepare a fair 937to decode or encode properly, so it was impossible to prepare a fair
575comparison table for that case. 938comparison table for that case.
576 939
577=head1 RESOURCE LIMITS
578 940
579JSON::XS does not impose any limits on the size of JSON texts or Perl 941=head1 SECURITY CONSIDERATIONS
580values they represent - if your machine can handle it, JSON::XS will 942
581encode or decode it. Future versions might optionally impose structure 943When you are using JSON in a protocol, talking to untrusted potentially
582depth and memory use resource limits. 944hostile creatures requires relatively few measures.
945
946First of all, your JSON decoder should be secure, that is, should not have
947any buffer overflows. Obviously, this module should ensure that and I am
948trying hard on making that true, but you never know.
949
950Second, you need to avoid resource-starving attacks. That means you should
951limit the size of JSON texts you accept, or make sure then when your
952resources run out, that's just fine (e.g. by using a separate process that
953can crash safely). The size of a JSON text in octets or characters is
954usually a good indication of the size of the resources required to decode
955it into a Perl structure. While JSON::XS can check the size of the JSON
956text, it might be too late when you already have it in memory, so you
957might want to check the size before you accept the string.
958
959Third, JSON::XS recurses using the C stack when decoding objects and
960arrays. The C stack is a limited resource: for instance, on my amd64
961machine with 8MB of stack size I can decode around 180k nested arrays but
962only 14k nested JSON objects (due to perl itself recursing deeply on croak
963to free the temporary). If that is exceeded, the program crashes. to be
964conservative, the default nesting limit is set to 512. If your process
965has a smaller stack, you should adjust this setting accordingly with the
966C<max_depth> method.
967
968And last but least, something else could bomb you that I forgot to think
969of. In that case, you get to keep the pieces. I am always open for hints,
970though...
971
972If you are using JSON::XS to return packets to consumption
973by JavaScript scripts in a browser you should have a look at
974L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
975you are vulnerable to some common attack vectors (which really are browser
976design bugs, but it is still you who will have to deal with it, as major
977browser developers care only for features, not about doing security
978right).
979
980
981=head1 THREADS
982
983This module is I<not> guaranteed to be thread safe and there are no
984plans to change this until Perl gets thread support (as opposed to the
985horribly slow so-called "threads" which are simply slow and bloated
986process simulations - use fork, its I<much> faster, cheaper, better).
987
988(It might actually work, but you have been warned).
989
583 990
584=head1 BUGS 991=head1 BUGS
585 992
586While the goal of this module is to be correct, that unfortunately does 993While the goal of this module is to be correct, that unfortunately does
587not mean its bug-free, only that I think its design is bug-free. It is 994not mean its bug-free, only that I think its design is bug-free. It is
588still very young and not well-tested. If you keep reporting bugs they will 995still relatively early in its development. If you keep reporting bugs they
589be fixed swiftly, though. 996will be fixed swiftly, though.
997
998Please refrain from using rt.cpan.org or any other bug reporting
999service. I put the contact address into my modules for a reason.
590 1000
591=cut 1001=cut
1002
1003our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
1004our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
1005
1006sub true() { $true }
1007sub false() { $false }
1008
1009sub is_bool($) {
1010 UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
1011# or UNIVERSAL::isa $_[0], "JSON::Literal"
1012}
1013
1014XSLoader::load "JSON::XS", $VERSION;
1015
1016package JSON::XS::Boolean;
1017
1018use overload
1019 "0+" => sub { ${$_[0]} },
1020 "++" => sub { $_[0] = ${$_[0]} + 1 },
1021 "--" => sub { $_[0] = ${$_[0]} - 1 },
1022 fallback => 1;
592 1023
5931; 10241;
594 1025
595=head1 AUTHOR 1026=head1 AUTHOR
596 1027

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