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Revision 1.10 by root, Fri Mar 23 17:40:29 2007 UTC vs.
Revision 1.63 by root, Thu Oct 11 23:07:43 2007 UTC

1=encoding utf-8
2
1=head1 NAME 3=head1 NAME
2 4
3JSON::XS - JSON serialising/deserialising, done correctly and fast 5JSON::XS - JSON serialising/deserialising, done correctly and fast
4 6
7JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
8 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
9
5=head1 SYNOPSIS 10=head1 SYNOPSIS
6 11
7 use JSON::XS; 12 use JSON::XS;
13
14 # exported functions, they croak on error
15 # and expect/generate UTF-8
16
17 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
18 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text;
19
20 # OO-interface
21
22 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
23 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
24 $perl_scalar = $coder->decode ($unicode_json_text);
8 25
9=head1 DESCRIPTION 26=head1 DESCRIPTION
10 27
11This module converts Perl data structures to JSON and vice versa. Its 28This module converts Perl data structures to JSON and vice versa. Its
12primary goal is to be I<correct> and its secondary goal is to be 29primary goal is to be I<correct> and its secondary goal is to be
25 42
26=head2 FEATURES 43=head2 FEATURES
27 44
28=over 4 45=over 4
29 46
30=item * correct handling of unicode issues 47=item * correct unicode handling
31 48
32This module knows how to handle Unicode, and even documents how and when 49This module knows how to handle Unicode, and even documents how and when
33it does so. 50it does so.
34 51
35=item * round-trip integrity 52=item * round-trip integrity
36 53
37When you serialise a perl data structure using only datatypes supported 54When you serialise a perl data structure using only datatypes supported
38by JSON, the deserialised data structure is identical on the Perl level. 55by JSON, the deserialised data structure is identical on the Perl level.
39(e.g. the string "2.0" doesn't suddenly become "2"). 56(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
57like a number).
40 58
41=item * strict checking of JSON correctness 59=item * strict checking of JSON correctness
42 60
43There is no guessing, no generating of illegal JSON strings by default, 61There is no guessing, no generating of illegal JSON texts by default,
44and only JSON is accepted as input by default (the latter is a security 62and only JSON is accepted as input by default (the latter is a security
45feature). 63feature).
46 64
47=item * fast 65=item * fast
48 66
55interface. 73interface.
56 74
57=item * reasonably versatile output formats 75=item * reasonably versatile output formats
58 76
59You can choose between the most compact guarenteed single-line format 77You can choose between the most compact guarenteed single-line format
60possible (nice for simple line-based protocols), a pure-ascii format (for 78possible (nice for simple line-based protocols), a pure-ascii format
61when your transport is not 8-bit clean), or a pretty-printed format (for 79(for when your transport is not 8-bit clean, still supports the whole
62when you want to read that stuff). Or you can combine those features in 80unicode range), or a pretty-printed format (for when you want to read that
63whatever way you like. 81stuff). Or you can combine those features in whatever way you like.
64 82
65=back 83=back
66 84
67=cut 85=cut
68 86
69package JSON::XS; 87package JSON::XS;
70 88
71BEGIN { 89use strict;
90
72 $VERSION = '0.3'; 91our $VERSION = '1.5';
73 @ISA = qw(Exporter); 92our @ISA = qw(Exporter);
74 93
75 @EXPORT = qw(to_json from_json); 94our @EXPORT = qw(to_json from_json);
76 require Exporter;
77 95
78 require XSLoader; 96use Exporter;
79 XSLoader::load JSON::XS::, $VERSION; 97use XSLoader;
80}
81 98
82=head1 FUNCTIONAL INTERFACE 99=head1 FUNCTIONAL INTERFACE
83 100
84The following convinience methods are provided by this module. They are 101The following convinience methods are provided by this module. They are
85exported by default: 102exported by default:
86 103
87=over 4 104=over 4
88 105
89=item $json_string = to_json $perl_scalar 106=item $json_text = to_json $perl_scalar
90 107
91Converts the given Perl data structure (a simple scalar or a reference to 108Converts the given Perl data structure to a UTF-8 encoded, binary string
92a hash or array) to a UTF-8 encoded, binary string (that is, the string contains 109(that is, the string contains octets only). Croaks on error.
93octets only). Croaks on error.
94 110
95This function call is functionally identical to C<< JSON::XS->new->utf8->encode ($perl_scalar) >>. 111This function call is functionally identical to:
96 112
113 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
114
115except being faster.
116
97=item $perl_scalar = from_json $json_string 117=item $perl_scalar = from_json $json_text
98 118
99The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to 119The opposite of C<to_json>: expects an UTF-8 (binary) string and tries
100parse that as an UTF-8 encoded JSON string, returning the resulting simple 120to parse that as an UTF-8 encoded JSON text, returning the resulting
101scalar or reference. Croaks on error. 121reference. Croaks on error.
102 122
103This function call is functionally identical to C<< JSON::XS->new->utf8->decode ($json_string) >>. 123This function call is functionally identical to:
124
125 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
126
127except being faster.
128
129=item $is_boolean = JSON::XS::is_bool $scalar
130
131Returns true if the passed scalar represents either JSON::XS::true or
132JSON::XS::false, two constants that act like C<1> and C<0>, respectively
133and are used to represent JSON C<true> and C<false> values in Perl.
134
135See MAPPING, below, for more information on how JSON values are mapped to
136Perl.
104 137
105=back 138=back
139
140
141=head1 A FEW NOTES ON UNICODE AND PERL
142
143Since this often leads to confusion, here are a few very clear words on
144how Unicode works in Perl, modulo bugs.
145
146=over 4
147
148=item 1. Perl strings can store characters with ordinal values > 255.
149
150This enables you to store unicode characters as single characters in a
151Perl string - very natural.
152
153=item 2. Perl does I<not> associate an encoding with your strings.
154
155Unless you force it to, e.g. when matching it against a regex, or printing
156the scalar to a file, in which case Perl either interprets your string as
157locale-encoded text, octets/binary, or as Unicode, depending on various
158settings. In no case is an encoding stored together with your data, it is
159I<use> that decides encoding, not any magical metadata.
160
161=item 3. The internal utf-8 flag has no meaning with regards to the
162encoding of your string.
163
164Just ignore that flag unless you debug a Perl bug, a module written in
165XS or want to dive into the internals of perl. Otherwise it will only
166confuse you, as, despite the name, it says nothing about how your string
167is encoded. You can have unicode strings with that flag set, with that
168flag clear, and you can have binary data with that flag set and that flag
169clear. Other possibilities exist, too.
170
171If you didn't know about that flag, just the better, pretend it doesn't
172exist.
173
174=item 4. A "Unicode String" is simply a string where each character can be
175validly interpreted as a Unicode codepoint.
176
177If you have UTF-8 encoded data, it is no longer a Unicode string, but a
178Unicode string encoded in UTF-8, giving you a binary string.
179
180=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
181
182Its a fact. Learn to live with it.
183
184=back
185
186I hope this helps :)
187
106 188
107=head1 OBJECT-ORIENTED INTERFACE 189=head1 OBJECT-ORIENTED INTERFACE
108 190
109The object oriented interface lets you configure your own encoding or 191The object oriented interface lets you configure your own encoding or
110decoding style, within the limits of supported formats. 192decoding style, within the limits of supported formats.
117strings. All boolean flags described below are by default I<disabled>. 199strings. All boolean flags described below are by default I<disabled>.
118 200
119The mutators for flags all return the JSON object again and thus calls can 201The mutators for flags all return the JSON object again and thus calls can
120be chained: 202be chained:
121 203
122 my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]}) 204 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
123 => {"a": [1, 2]} 205 => {"a": [1, 2]}
124 206
125=item $json = $json->ascii ([$enable]) 207=item $json = $json->ascii ([$enable])
126 208
127If C<$enable> is true (or missing), then the C<encode> method will 209If C<$enable> is true (or missing), then the C<encode> method will not
128not generate characters outside the code range C<0..127>. Any unicode 210generate characters outside the code range C<0..127> (which is ASCII). Any
129characters outside that range will be escaped using either a single 211unicode characters outside that range will be escaped using either a
130\uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, as per 212single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
131RFC4627. 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.
132 216
133If 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
134characters unless necessary. 218characters unless required by the JSON syntax or other flags. This results
219in a faster and more compact format.
135 220
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.
224
136 JSON::XS->new->ascii (1)->encode (chr 0x10401) 225 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
137 => \ud801\udc01 226 => ["\ud801\udc01"]
227
228=item $json = $json->latin1 ([$enable])
229
230If C<$enable> is true (or missing), then the C<encode> method will encode
231the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
232outside the code range C<0..255>. The resulting string can be treated as a
233latin1-encoded JSON text or a native unicode string. The C<decode> method
234will not be affected in any way by this flag, as C<decode> by default
235expects unicode, which is a strict superset of latin1.
236
237If C<$enable> is false, then the C<encode> method will not escape Unicode
238characters unless required by the JSON syntax or other flags.
239
240The main use for this flag is efficiently encoding binary data as JSON
241text, as most octets will not be escaped, resulting in a smaller encoded
242size. The disadvantage is that the resulting JSON text is encoded
243in latin1 (and must correctly be treated as such when storing and
244transfering), a rare encoding for JSON. It is therefore most useful when
245you want to store data structures known to contain binary data efficiently
246in files or databases, not when talking to other JSON encoders/decoders.
247
248 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
249 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
138 250
139=item $json = $json->utf8 ([$enable]) 251=item $json = $json->utf8 ([$enable])
140 252
141If C<$enable> is true (or missing), then the C<encode> method will encode 253If C<$enable> is true (or missing), then the C<encode> method will encode
142the JSON string into UTF-8, as required by many protocols, while the 254the JSON result into UTF-8, as required by many protocols, while the
143C<decode> method expects to be handled an UTF-8-encoded string. Please 255C<decode> method expects to be handled an UTF-8-encoded string. Please
144note that UTF-8-encoded strings do not contain any characters outside the 256note that UTF-8-encoded strings do not contain any characters outside the
145range C<0..255>, they are thus useful for bytewise/binary I/O. 257range C<0..255>, they are thus useful for bytewise/binary I/O. In future
258versions, enabling this option might enable autodetection of the UTF-16
259and UTF-32 encoding families, as described in RFC4627.
146 260
147If C<$enable> is false, then the C<encode> method will return the JSON 261If C<$enable> is false, then the C<encode> method will return the JSON
148string as a (non-encoded) unicode string, while C<decode> expects thus a 262string as a (non-encoded) unicode string, while C<decode> expects thus a
149unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs 263unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
150to be done yourself, e.g. using the Encode module. 264to be done yourself, e.g. using the Encode module.
151 265
266Example, output UTF-16BE-encoded JSON:
267
268 use Encode;
269 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
270
271Example, decode UTF-32LE-encoded JSON:
272
273 use Encode;
274 $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
275
152=item $json = $json->pretty ([$enable]) 276=item $json = $json->pretty ([$enable])
153 277
154This enables (or disables) all of the C<indent>, C<space_before> and 278This enables (or disables) all of the C<indent>, C<space_before> and
155C<space_after> (and in the future possibly more) flags in one call to 279C<space_after> (and in the future possibly more) flags in one call to
156generate the most readable (or most compact) form possible. 280generate the most readable (or most compact) form possible.
281
282Example, pretty-print some simple structure:
157 283
158 my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) 284 my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
159 => 285 =>
160 { 286 {
161 "a" : [ 287 "a" : [
169If C<$enable> is true (or missing), then the C<encode> method will use a multiline 295If C<$enable> is true (or missing), then the C<encode> method will use a multiline
170format as output, putting every array member or object/hash key-value pair 296format as output, putting every array member or object/hash key-value pair
171into its own line, identing them properly. 297into its own line, identing them properly.
172 298
173If C<$enable> is false, no newlines or indenting will be produced, and the 299If C<$enable> is false, no newlines or indenting will be produced, and the
174resulting JSON strings is guarenteed not to contain any C<newlines>. 300resulting JSON text is guarenteed not to contain any C<newlines>.
175 301
176This setting has no effect when decoding JSON strings. 302This setting has no effect when decoding JSON texts.
177 303
178=item $json = $json->space_before ([$enable]) 304=item $json = $json->space_before ([$enable])
179 305
180If C<$enable> is true (or missing), then the C<encode> method will add an extra 306If C<$enable> is true (or missing), then the C<encode> method will add an extra
181optional space before the C<:> separating keys from values in JSON objects. 307optional space before the C<:> separating keys from values in JSON objects.
182 308
183If C<$enable> is false, then the C<encode> method will not add any extra 309If C<$enable> is false, then the C<encode> method will not add any extra
184space at those places. 310space at those places.
185 311
186This setting has no effect when decoding JSON strings. You will also most 312This setting has no effect when decoding JSON texts. You will also
187likely combine this setting with C<space_after>. 313most likely combine this setting with C<space_after>.
314
315Example, space_before enabled, space_after and indent disabled:
316
317 {"key" :"value"}
188 318
189=item $json = $json->space_after ([$enable]) 319=item $json = $json->space_after ([$enable])
190 320
191If C<$enable> is true (or missing), then the C<encode> method will add an extra 321If C<$enable> is true (or missing), then the C<encode> method will add an extra
192optional space after the C<:> separating keys from values in JSON objects 322optional space after the C<:> separating keys from values in JSON objects
194members. 324members.
195 325
196If C<$enable> is false, then the C<encode> method will not add any extra 326If C<$enable> is false, then the C<encode> method will not add any extra
197space at those places. 327space at those places.
198 328
199This setting has no effect when decoding JSON strings. 329This setting has no effect when decoding JSON texts.
330
331Example, space_before and indent disabled, space_after enabled:
332
333 {"key": "value"}
334
335=item $json = $json->relaxed ([$enable])
336
337If C<$enable> is true (or missing), then C<decode> will accept some
338extensions to normal JSON syntax (see below). C<encode> will not be
339affected in anyway. I<Be aware that this option makes you accept invalid
340JSON texts as if they were valid!>. I suggest only to use this option to
341parse application-specific files written by humans (configuration files,
342resource files etc.)
343
344If C<$enable> is false (the default), then C<decode> will only accept
345valid JSON texts.
346
347Currently accepted extensions are:
348
349=over 4
350
351=item * list items can have an end-comma
352
353JSON I<separates> array elements and key-value pairs with commas. This
354can be annoying if you write JSON texts manually and want to be able to
355quickly append elements, so this extension accepts comma at the end of
356such items not just between them:
357
358 [
359 1,
360 2, <- this comma not normally allowed
361 ]
362 {
363 "k1": "v1",
364 "k2": "v2", <- this comma not normally allowed
365 }
366
367=item * shell-style '#'-comments
368
369Whenever JSON allows whitespace, shell-style comments are additionally
370allowed. They are terminated by the first carriage-return or line-feed
371character, after which more white-space and comments are allowed.
372
373 [
374 1, # this comment not allowed in JSON
375 # neither this one...
376 ]
377
378=back
200 379
201=item $json = $json->canonical ([$enable]) 380=item $json = $json->canonical ([$enable])
202 381
203If C<$enable> is true (or missing), then the C<encode> method will output JSON objects 382If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
204by sorting their keys. This is adding a comparatively high overhead. 383by sorting their keys. This is adding a comparatively high overhead.
206If C<$enable> is false, then the C<encode> method will output key-value 385If C<$enable> is false, then the C<encode> method will output key-value
207pairs in the order Perl stores them (which will likely change between runs 386pairs in the order Perl stores them (which will likely change between runs
208of the same script). 387of the same script).
209 388
210This option is useful if you want the same data structure to be encoded as 389This option is useful if you want the same data structure to be encoded as
211the same JSON string (given the same overall settings). If it is disabled, 390the same JSON text (given the same overall settings). If it is disabled,
212the same hash migh be encoded differently even if contains the same data, 391the same hash migh be encoded differently even if contains the same data,
213as key-value pairs have no inherent ordering in Perl. 392as key-value pairs have no inherent ordering in Perl.
214 393
215This setting has no effect when decoding JSON strings. 394This setting has no effect when decoding JSON texts.
216 395
217=item $json = $json->allow_nonref ([$enable]) 396=item $json = $json->allow_nonref ([$enable])
218 397
219If C<$enable> is true (or missing), then the C<encode> method can convert a 398If C<$enable> is true (or missing), then the C<encode> method can convert a
220non-reference into its corresponding string, number or null JSON value, 399non-reference into its corresponding string, number or null JSON value,
221which is an extension to RFC4627. Likewise, C<decode> will accept those JSON 400which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
222values instead of croaking. 401values instead of croaking.
223 402
224If C<$enable> is false, then the C<encode> method will croak if it isn't 403If C<$enable> is false, then the C<encode> method will croak if it isn't
225passed an arrayref or hashref, as JSON strings must either be an object 404passed an arrayref or hashref, as JSON texts must either be an object
226or array. Likewise, C<decode> will croak if given something that is not a 405or array. Likewise, C<decode> will croak if given something that is not a
227JSON object or array. 406JSON object or array.
228 407
408Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
409resulting in an invalid JSON text:
410
411 JSON::XS->new->allow_nonref->encode ("Hello, World!")
412 => "Hello, World!"
413
414=item $json = $json->allow_blessed ([$enable])
415
416If C<$enable> is true (or missing), then the C<encode> method will not
417barf when it encounters a blessed reference. Instead, the value of the
418B<convert_blessed> option will decide wether C<null> (C<convert_blessed>
419disabled or no C<to_json> method found) or a representation of the
420object (C<convert_blessed> enabled and C<to_json> method found) is being
421encoded. Has no effect on C<decode>.
422
423If C<$enable> is false (the default), then C<encode> will throw an
424exception when it encounters a blessed object.
425
426=item $json = $json->convert_blessed ([$enable])
427
428If C<$enable> is true (or missing), then C<encode>, upon encountering a
429blessed object, will check for the availability of the C<TO_JSON> method
430on the object's class. If found, it will be called in scalar context
431and the resulting scalar will be encoded instead of the object. If no
432C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
433to do.
434
435The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
436returns other blessed objects, those will be handled in the same
437way. C<TO_JSON> must take care of not causing an endless recursion cycle
438(== crash) in this case. The name of C<TO_JSON> was chosen because other
439methods called by the Perl core (== not by the user of the object) are
440usually in upper case letters and to avoid collisions with the C<to_json>
441function.
442
443This setting does not yet influence C<decode> in any way, but in the
444future, global hooks might get installed that influence C<decode> and are
445enabled by this setting.
446
447If C<$enable> is false, then the C<allow_blessed> setting will decide what
448to do when a blessed object is found.
449
450=item $json = $json->filter_json_object ([$coderef->($hashref)])
451
452When C<$coderef> is specified, it will be called from C<decode> each
453time it decodes a JSON object. The only argument is a reference to the
454newly-created hash. If the code references returns a single scalar (which
455need not be a reference), this value (i.e. a copy of that scalar to avoid
456aliasing) is inserted into the deserialised data structure. If it returns
457an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
458original deserialised hash will be inserted. This setting can slow down
459decoding considerably.
460
461When C<$coderef> is omitted or undefined, any existing callback will
462be removed and C<decode> will not change the deserialised hash in any
463way.
464
465Example, convert all JSON objects into the integer 5:
466
467 my $js = JSON::XS->new->filter_json_object (sub { 5 });
468 # returns [5]
469 $js->decode ('[{}]')
470 # throw an exception because allow_nonref is not enabled
471 # so a lone 5 is not allowed.
472 $js->decode ('{"a":1, "b":2}');
473
474=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
475
476Works remotely similar to C<filter_json_object>, but is only called for
477JSON objects having a single key named C<$key>.
478
479This C<$coderef> is called before the one specified via
480C<filter_json_object>, if any. It gets passed the single value in the JSON
481object. If it returns a single value, it will be inserted into the data
482structure. If it returns nothing (not even C<undef> but the empty list),
483the callback from C<filter_json_object> will be called next, as if no
484single-key callback were specified.
485
486If C<$coderef> is omitted or undefined, the corresponding callback will be
487disabled. There can only ever be one callback for a given key.
488
489As this callback gets called less often then the C<filter_json_object>
490one, decoding speed will not usually suffer as much. Therefore, single-key
491objects make excellent targets to serialise Perl objects into, especially
492as single-key JSON objects are as close to the type-tagged value concept
493as JSON gets (its basically an ID/VALUE tuple). Of course, JSON does not
494support this in any way, so you need to make sure your data never looks
495like a serialised Perl hash.
496
497Typical names for the single object key are C<__class_whatever__>, or
498C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
499things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
500with real hashes.
501
502Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
503into the corresponding C<< $WIDGET{<id>} >> object:
504
505 # return whatever is in $WIDGET{5}:
506 JSON::XS
507 ->new
508 ->filter_json_single_key_object (__widget__ => sub {
509 $WIDGET{ $_[0] }
510 })
511 ->decode ('{"__widget__": 5')
512
513 # this can be used with a TO_JSON method in some "widget" class
514 # for serialisation to json:
515 sub WidgetBase::TO_JSON {
516 my ($self) = @_;
517
518 unless ($self->{id}) {
519 $self->{id} = ..get..some..id..;
520 $WIDGET{$self->{id}} = $self;
521 }
522
523 { __widget__ => $self->{id} }
524 }
525
229=item $json = $json->shrink ([$enable]) 526=item $json = $json->shrink ([$enable])
230 527
231Perl usually over-allocates memory a bit when allocating space for 528Perl usually over-allocates memory a bit when allocating space for
232strings. This flag optionally resizes strings generated by either 529strings. This flag optionally resizes strings generated by either
233C<encode> or C<decode> to their minimum size possible. This can save 530C<encode> or C<decode> to their minimum size possible. This can save
234memory when your JSON strings are either very very long or you have many 531memory when your JSON texts are either very very long or you have many
235short strings. It will also try to downgrade any strings to octet-form 532short strings. It will also try to downgrade any strings to octet-form
236if possible: perl stores strings internally either in an encoding called 533if possible: perl stores strings internally either in an encoding called
237UTF-X or in octet-form. The latter cannot store everything but uses less 534UTF-X or in octet-form. The latter cannot store everything but uses less
238space in general. 535space in general (and some buggy Perl or C code might even rely on that
536internal representation being used).
239 537
538The actual definition of what shrink does might change in future versions,
539but it will always try to save space at the expense of time.
540
240If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit, 541If C<$enable> is true (or missing), the string returned by C<encode> will
241while all strings generated by C<decode> will also be shrunk-to-fit. 542be shrunk-to-fit, while all strings generated by C<decode> will also be
543shrunk-to-fit.
242 544
243If C<$enable> is false, then the normal perl allocation algorithms are used. 545If C<$enable> is false, then the normal perl allocation algorithms are used.
244If you work with your data, then this is likely to be faster. 546If you work with your data, then this is likely to be faster.
245 547
246In the future, this setting might control other things, such as converting 548In the future, this setting might control other things, such as converting
247strings that look like integers or floats into integers or floats 549strings that look like integers or floats into integers or floats
248internally (there is no difference on the Perl level), saving space. 550internally (there is no difference on the Perl level), saving space.
249 551
552=item $json = $json->max_depth ([$maximum_nesting_depth])
553
554Sets the maximum nesting level (default C<512>) accepted while encoding
555or decoding. If the JSON text or Perl data structure has an equal or
556higher nesting level then this limit, then the encoder and decoder will
557stop and croak at that point.
558
559Nesting level is defined by number of hash- or arrayrefs that the encoder
560needs to traverse to reach a given point or the number of C<{> or C<[>
561characters without their matching closing parenthesis crossed to reach a
562given character in a string.
563
564Setting the maximum depth to one disallows any nesting, so that ensures
565that the object is only a single hash/object or array.
566
567The argument to C<max_depth> will be rounded up to the next highest power
568of two. If no argument is given, the highest possible setting will be
569used, which is rarely useful.
570
571See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
572
573=item $json = $json->max_size ([$maximum_string_size])
574
575Set the maximum length a JSON text may have (in bytes) where decoding is
576being attempted. The default is C<0>, meaning no limit. When C<decode>
577is called on a string longer then this number of characters it will not
578attempt to decode the string but throw an exception. This setting has no
579effect on C<encode> (yet).
580
581The argument to C<max_size> will be rounded up to the next B<highest>
582power of two (so may be more than requested). If no argument is given, the
583limit check will be deactivated (same as when C<0> is specified).
584
585See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
586
250=item $json_string = $json->encode ($perl_scalar) 587=item $json_text = $json->encode ($perl_scalar)
251 588
252Converts the given Perl data structure (a simple scalar or a reference 589Converts the given Perl data structure (a simple scalar or a reference
253to a hash or array) to its JSON representation. Simple scalars will be 590to a hash or array) to its JSON representation. Simple scalars will be
254converted into JSON string or number sequences, while references to arrays 591converted into JSON string or number sequences, while references to arrays
255become JSON arrays and references to hashes become JSON objects. Undefined 592become JSON arrays and references to hashes become JSON objects. Undefined
256Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true> 593Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
257nor C<false> values will be generated. 594nor C<false> values will be generated.
258 595
259=item $perl_scalar = $json->decode ($json_string) 596=item $perl_scalar = $json->decode ($json_text)
260 597
261The opposite of C<encode>: expects a JSON string and tries to parse it, 598The opposite of C<encode>: expects a JSON text and tries to parse it,
262returning the resulting simple scalar or reference. Croaks on error. 599returning the resulting simple scalar or reference. Croaks on error.
263 600
264JSON numbers and strings become simple Perl scalars. JSON arrays become 601JSON numbers and strings become simple Perl scalars. JSON arrays become
265Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes 602Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
266C<1>, C<false> becomes C<0> and C<null> becomes C<undef>. 603C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
267 604
605=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
606
607This works like the C<decode> method, but instead of raising an exception
608when there is trailing garbage after the first JSON object, it will
609silently stop parsing there and return the number of characters consumed
610so far.
611
612This is useful if your JSON texts are not delimited by an outer protocol
613(which is not the brightest thing to do in the first place) and you need
614to know where the JSON text ends.
615
616 JSON::XS->new->decode_prefix ("[1] the tail")
617 => ([], 3)
618
268=back 619=back
620
269 621
270=head1 MAPPING 622=head1 MAPPING
271 623
272This section describes how JSON::XS maps Perl values to JSON values and 624This section describes how JSON::XS maps Perl values to JSON values and
273vice versa. These mappings are designed to "do the right thing" in most 625vice versa. These mappings are designed to "do the right thing" in most
276 628
277For the more enlightened: note that in the following descriptions, 629For the more enlightened: note that in the following descriptions,
278lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl> 630lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>
279refers to the abstract Perl language itself. 631refers to the abstract Perl language itself.
280 632
633
281=head2 JSON -> PERL 634=head2 JSON -> PERL
282 635
283=over 4 636=over 4
284 637
285=item object 638=item object
286 639
287A JSON object becomes a reference to a hash in Perl. No ordering of object 640A JSON object becomes a reference to a hash in Perl. No ordering of object
288keys is preserved. 641keys is preserved (JSON does not preserver object key ordering itself).
289 642
290=item array 643=item array
291 644
292A JSON array becomes a reference to an array in Perl. 645A JSON array becomes a reference to an array in Perl.
293 646
297are represented by the same codepoints in the Perl string, so no manual 650are represented by the same codepoints in the Perl string, so no manual
298decoding is necessary. 651decoding is necessary.
299 652
300=item number 653=item number
301 654
302A JSON number becomes either an integer or numeric (floating point) 655A JSON number becomes either an integer, numeric (floating point) or
303scalar in perl, depending on its range and any fractional parts. On the 656string scalar in perl, depending on its range and any fractional parts. On
304Perl level, there is no difference between those as Perl handles all the 657the Perl level, there is no difference between those as Perl handles all
305conversion details, but an integer may take slightly less memory and might 658the conversion details, but an integer may take slightly less memory and
306represent more values exactly than (floating point) numbers. 659might represent more values exactly than (floating point) numbers.
660
661If the number consists of digits only, JSON::XS will try to represent
662it as an integer value. If that fails, it will try to represent it as
663a numeric (floating point) value if that is possible without loss of
664precision. Otherwise it will preserve the number as a string value.
665
666Numbers containing a fractional or exponential part will always be
667represented as numeric (floating point) values, possibly at a loss of
668precision.
669
670This might create round-tripping problems as numbers might become strings,
671but as Perl is typeless there is no other way to do it.
307 672
308=item true, false 673=item true, false
309 674
310These JSON atoms become C<0>, C<1>, respectively. Information is lost in 675These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
311this process. Future versions might represent those values differently, 676respectively. They are overloaded to act almost exactly like the numbers
312but they will be guarenteed to act like these integers would normally in 677C<1> and C<0>. You can check wether a scalar is a JSON boolean by using
313Perl. 678the C<JSON::XS::is_bool> function.
314 679
315=item null 680=item null
316 681
317A JSON null atom becomes C<undef> in Perl. 682A JSON null atom becomes C<undef> in Perl.
318 683
319=back 684=back
685
320 686
321=head2 PERL -> JSON 687=head2 PERL -> JSON
322 688
323The mapping from Perl to JSON is slightly more difficult, as Perl is a 689The mapping from Perl to JSON is slightly more difficult, as Perl is a
324truly typeless language, so we can only guess which JSON type is meant by 690truly typeless language, so we can only guess which JSON type is meant by
327=over 4 693=over 4
328 694
329=item hash references 695=item hash references
330 696
331Perl hash references become JSON objects. As there is no inherent ordering 697Perl hash references become JSON objects. As there is no inherent ordering
332in hash keys, they will usually be encoded in a pseudo-random order that 698in hash keys (or JSON objects), they will usually be encoded in a
333can change between runs of the same program but stays generally the same 699pseudo-random order that can change between runs of the same program but
334within the single run of a program. JSON::XS can optionally sort the hash 700stays generally the same within a single run of a program. JSON::XS can
335keys (determined by the I<canonical> flag), so the same datastructure 701optionally sort the hash keys (determined by the I<canonical> flag), so
336will serialise to the same JSON text (given same settings and version of 702the same datastructure will serialise to the same JSON text (given same
337JSON::XS), but this incurs a runtime overhead. 703settings and version of JSON::XS), but this incurs a runtime overhead
704and is only rarely useful, e.g. when you want to compare some JSON text
705against another for equality.
338 706
339=item array references 707=item array references
340 708
341Perl array references become JSON arrays. 709Perl array references become JSON arrays.
710
711=item other references
712
713Other unblessed references are generally not allowed and will cause an
714exception to be thrown, except for references to the integers C<0> and
715C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
716also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
717
718 to_json [\0,JSON::XS::true] # yields [false,true]
719
720=item JSON::XS::true, JSON::XS::false
721
722These special values become JSON true and JSON false values,
723respectively. You can also use C<\1> and C<\0> directly if you want.
342 724
343=item blessed objects 725=item blessed objects
344 726
345Blessed objects are not allowed. JSON::XS currently tries to encode their 727Blessed objects are not allowed. JSON::XS currently tries to encode their
346underlying representation (hash- or arrayref), but this behaviour might 728underlying representation (hash- or arrayref), but this behaviour might
380 762
381You can not currently output JSON booleans or force the type in other, 763You can not currently output JSON booleans or force the type in other,
382less obscure, ways. Tell me if you need this capability. 764less obscure, ways. Tell me if you need this capability.
383 765
384=back 766=back
767
385 768
386=head1 COMPARISON 769=head1 COMPARISON
387 770
388As already mentioned, this module was created because none of the existing 771As already mentioned, this module was created because none of the existing
389JSON modules could be made to work correctly. First I will describe the 772JSON modules could be made to work correctly. First I will describe the
415 798
416Has problems handling many Perl values (e.g. regex results and other magic 799Has problems handling many Perl values (e.g. regex results and other magic
417values will make it croak). 800values will make it croak).
418 801
419Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> 802Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
420which is not a valid JSON string. 803which is not a valid JSON text.
421 804
422Unmaintained (maintainer unresponsive for many months, bugs are not 805Unmaintained (maintainer unresponsive for many months, bugs are not
423getting fixed). 806getting fixed).
424 807
425=item JSON::Syck 0.21 808=item JSON::Syck 0.21
427Very buggy (often crashes). 810Very buggy (often crashes).
428 811
429Very inflexible (no human-readable format supported, format pretty much 812Very inflexible (no human-readable format supported, format pretty much
430undocumented. I need at least a format for easy reading by humans and a 813undocumented. I need at least a format for easy reading by humans and a
431single-line compact format for use in a protocol, and preferably a way to 814single-line compact format for use in a protocol, and preferably a way to
432generate ASCII-only JSON strings). 815generate ASCII-only JSON texts).
433 816
434Completely broken (and confusingly documented) Unicode handling (unicode 817Completely broken (and confusingly documented) Unicode handling (unicode
435escapes are not working properly, you need to set ImplicitUnicode to 818escapes are not working properly, you need to set ImplicitUnicode to
436I<different> values on en- and decoding to get symmetric behaviour). 819I<different> values on en- and decoding to get symmetric behaviour).
437 820
460 843
461Very inflexible. 844Very inflexible.
462 845
463No roundtripping. 846No roundtripping.
464 847
465Does not generate valid JSON (key strings are often unquoted, empty keys 848Does not generate valid JSON texts (key strings are often unquoted, empty keys
466result in nothing being output) 849result in nothing being output)
467 850
468Does not check input for validity. 851Does not check input for validity.
469 852
470=back 853=back
854
855
856=head2 JSON and YAML
857
858You often hear that JSON is a subset (or a close subset) of YAML. This is,
859however, a mass hysteria and very far from the truth. In general, there is
860no way to configure JSON::XS to output a data structure as valid YAML.
861
862If you really must use JSON::XS to generate YAML, you should use this
863algorithm (subject to change in future versions):
864
865 my $to_yaml = JSON::XS->new->utf8->space_after (1);
866 my $yaml = $to_yaml->encode ($ref) . "\n";
867
868This will usually generate JSON texts that also parse as valid
869YAML. Please note that YAML has hardcoded limits on (simple) object key
870lengths that JSON doesn't have, so you should make sure that your hash
871keys are noticably shorter than the 1024 characters YAML allows.
872
873There might be other incompatibilities that I am not aware of. In general
874you should not try to generate YAML with a JSON generator or vice versa,
875or try to parse JSON with a YAML parser or vice versa: chances are high
876that you will run into severe interoperability problems.
877
471 878
472=head2 SPEED 879=head2 SPEED
473 880
474It seems that JSON::XS is surprisingly fast, as shown in the following 881It seems that JSON::XS is surprisingly fast, as shown in the following
475tables. They have been generated with the help of the C<eg/bench> program 882tables. They have been generated with the help of the C<eg/bench> program
476in the JSON::XS distribution, to make it easy to compare on your own 883in the JSON::XS distribution, to make it easy to compare on your own
477system. 884system.
478 885
479First is a comparison between various modules using a very simple JSON 886First comes a comparison between various modules using a very short
887single-line JSON string:
888
889 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
890 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
891
480string, showing the number of encodes/decodes per second (JSON::XS is 892It shows the number of encodes/decodes per second (JSON::XS uses
481the functional interface, while JSON::XS/2 is the OO interface with 893the functional interface, while JSON::XS/2 uses the OO interface
482pretty-printing and hashkey sorting enabled). 894with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
895shrink). Higher is better:
483 896
897 Storable | 15779.925 | 14169.946 |
898 -----------+------------+------------+
484 module | encode | decode | 899 module | encode | decode |
485 -----------|------------|------------| 900 -----------|------------|------------|
486 JSON | 14006 | 6820 | 901 JSON | 4990.842 | 4088.813 |
487 JSON::DWIW | 200937 | 120386 | 902 JSON::DWIW | 51653.990 | 71575.154 |
488 JSON::PC | 85065 | 129366 | 903 JSON::PC | 65948.176 | 74631.744 |
489 JSON::Syck | 59898 | 44232 | 904 JSON::PP | 8931.652 | 3817.168 |
490 JSON::XS | 1171478 | 342435 | 905 JSON::Syck | 24877.248 | 27776.848 |
491 JSON::XS/2 | 730760 | 328714 | 906 JSON::XS | 388361.481 | 227951.304 |
907 JSON::XS/2 | 227951.304 | 218453.333 |
908 JSON::XS/3 | 338250.323 | 218453.333 |
909 Storable | 16500.016 | 135300.129 |
492 -----------+------------+------------+ 910 -----------+------------+------------+
493 911
494That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80 912That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
913about three times faster on decoding, and over fourty times faster
495times faster than JSON, even with pretty-printing and key sorting. 914than JSON, even with pretty-printing and key sorting. It also compares
915favourably to Storable for small amounts of data.
496 916
497Using a longer test string (roughly 8KB, generated from Yahoo! Locals 917Using a longer test string (roughly 18KB, generated from Yahoo! Locals
498search API (http://nanoref.com/yahooapis/mgPdGg): 918search API (http://nanoref.com/yahooapis/mgPdGg):
499 919
500 module | encode | decode | 920 module | encode | decode |
501 -----------|------------|------------| 921 -----------|------------|------------|
502 JSON | 673 | 38 | 922 JSON | 55.260 | 34.971 |
503 JSON::DWIW | 5271 | 770 | 923 JSON::DWIW | 825.228 | 1082.513 |
504 JSON::PC | 9901 | 2491 | 924 JSON::PC | 3571.444 | 2394.829 |
505 JSON::Syck | 2360 | 786 | 925 JSON::PP | 210.987 | 32.574 |
506 JSON::XS | 37398 | 3202 | 926 JSON::Syck | 552.551 | 787.544 |
507 JSON::XS/2 | 13765 | 3153 | 927 JSON::XS | 5780.463 | 4854.519 |
928 JSON::XS/2 | 3869.998 | 4798.975 |
929 JSON::XS/3 | 5862.880 | 4798.975 |
930 Storable | 4445.002 | 5235.027 |
508 -----------+------------+------------+ 931 -----------+------------+------------+
509 932
510Again, JSON::XS leads by far in the encoding case, while still beating 933Again, JSON::XS leads by far (except for Storable which non-surprisingly
511every other module in the decoding case. 934decodes faster).
512 935
513Last example is an almost 8MB large hash with many large binary values 936On large strings containing lots of high unicode characters, some modules
514(PNG files), resulting in a lot of escaping: 937(such as JSON::PC) seem to decode faster than JSON::XS, but the result
938will be broken due to missing (or wrong) unicode handling. Others refuse
939to decode or encode properly, so it was impossible to prepare a fair
940comparison table for that case.
941
942
943=head1 SECURITY CONSIDERATIONS
944
945When you are using JSON in a protocol, talking to untrusted potentially
946hostile creatures requires relatively few measures.
947
948First of all, your JSON decoder should be secure, that is, should not have
949any buffer overflows. Obviously, this module should ensure that and I am
950trying hard on making that true, but you never know.
951
952Second, you need to avoid resource-starving attacks. That means you should
953limit the size of JSON texts you accept, or make sure then when your
954resources run out, thats just fine (e.g. by using a separate process that
955can crash safely). The size of a JSON text in octets or characters is
956usually a good indication of the size of the resources required to decode
957it into a Perl structure. While JSON::XS can check the size of the JSON
958text, it might be too late when you already have it in memory, so you
959might want to check the size before you accept the string.
960
961Third, JSON::XS recurses using the C stack when decoding objects and
962arrays. The C stack is a limited resource: for instance, on my amd64
963machine with 8MB of stack size I can decode around 180k nested arrays but
964only 14k nested JSON objects (due to perl itself recursing deeply on croak
965to free the temporary). If that is exceeded, the program crashes. to be
966conservative, the default nesting limit is set to 512. If your process
967has a smaller stack, you should adjust this setting accordingly with the
968C<max_depth> method.
969
970And last but least, something else could bomb you that I forgot to think
971of. In that case, you get to keep the pieces. I am always open for hints,
972though...
973
974If you are using JSON::XS to return packets to consumption
975by javascript scripts in a browser you should have a look at
976L<http://jpsykes.com/47/practical-csrf-and-json-security> to see wether
977you are vulnerable to some common attack vectors (which really are browser
978design bugs, but it is still you who will have to deal with it, as major
979browser developers care only for features, not about doing security
980right).
981
515 982
516=head1 BUGS 983=head1 BUGS
517 984
518While the goal of this module is to be correct, that unfortunately does 985While the goal of this module is to be correct, that unfortunately does
519not mean its bug-free, only that I think its design is bug-free. It is 986not mean its bug-free, only that I think its design is bug-free. It is
520still very young and not well-tested. If you keep reporting bugs they will 987still relatively early in its development. If you keep reporting bugs they
521be fixed swiftly, though. 988will be fixed swiftly, though.
522 989
523=cut 990=cut
991
992our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
993our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
994
995sub true() { $true }
996sub false() { $false }
997
998sub is_bool($) {
999 UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
1000# or UNIVERSAL::isa $_[0], "JSON::Literal"
1001}
1002
1003XSLoader::load "JSON::XS", $VERSION;
1004
1005package JSON::XS::Boolean;
1006
1007use overload
1008 "0+" => sub { ${$_[0]} },
1009 "++" => sub { $_[0] = ${$_[0]} + 1 },
1010 "--" => sub { $_[0] = ${$_[0]} - 1 },
1011 fallback => 1;
524 1012
5251; 10131;
526 1014
527=head1 AUTHOR 1015=head1 AUTHOR
528 1016

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