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Revision 1.50 by root, Mon Jul 2 00:29:38 2007 UTC vs.
Revision 1.78 by root, Wed Dec 5 10:59:28 2007 UTC

1=head1 NAME 1=head1 NAME
2 2
3JSON::XS - JSON serialising/deserialising, done correctly and fast 3JSON::XS - JSON serialising/deserialising, done correctly and fast
4
5JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
6 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
4 7
5=head1 SYNOPSIS 8=head1 SYNOPSIS
6 9
7 use JSON::XS; 10 use JSON::XS;
8 11
9 # exported functions, they croak on error 12 # exported functions, they croak on error
10 # and expect/generate UTF-8 13 # and expect/generate UTF-8
11 14
12 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 15 $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
13 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 16 $perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
14 17
15 # OO-interface 18 # OO-interface
16 19
17 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 20 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
18 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 21 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
19 $perl_scalar = $coder->decode ($unicode_json_text); 22 $perl_scalar = $coder->decode ($unicode_json_text);
20 23
24 # Note that JSON version 2.0 and above will automatically use JSON::XS
25 # if available, at virtually no speed overhead either, so you should
26 # be able to just:
27
28 use JSON;
29
30 # and do the same things, except that you have a pure-perl fallback now.
31
21=head1 DESCRIPTION 32=head1 DESCRIPTION
22 33
23This module converts Perl data structures to JSON and vice versa. Its 34This module converts Perl data structures to JSON and vice versa. Its
24primary goal is to be I<correct> and its secondary goal is to be 35primary goal is to be I<correct> and its secondary goal is to be
25I<fast>. To reach the latter goal it was written in C. 36I<fast>. To reach the latter goal it was written in C.
37
38Beginning with version 2.0 of the JSON module, when both JSON and
39JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
40overriden) with no overhead due to emulation (by inheritign constructor
41and methods). If JSON::XS is not available, it will fall back to the
42compatible JSON::PP module as backend, so using JSON instead of JSON::XS
43gives you a portable JSON API that can be fast when you need and doesn't
44require a C compiler when that is a problem.
26 45
27As this is the n-th-something JSON module on CPAN, what was the reason 46As this is the n-th-something JSON module on CPAN, what was the reason
28to write yet another JSON module? While it seems there are many JSON 47to write yet another JSON module? While it seems there are many JSON
29modules, none of them correctly handle all corner cases, and in most cases 48modules, none of them correctly handle all corner cases, and in most cases
30their maintainers are unresponsive, gone missing, or not listening to bug 49their maintainers are unresponsive, gone missing, or not listening to bug
37 56
38=head2 FEATURES 57=head2 FEATURES
39 58
40=over 4 59=over 4
41 60
42=item * correct unicode handling 61=item * correct Unicode handling
43 62
44This module knows how to handle Unicode, and even documents how and when 63This module knows how to handle Unicode, and even documents how and when
45it does so. 64it does so.
46 65
47=item * round-trip integrity 66=item * round-trip integrity
67This module has both a simple functional interface as well as an OO 86This module has both a simple functional interface as well as an OO
68interface. 87interface.
69 88
70=item * reasonably versatile output formats 89=item * reasonably versatile output formats
71 90
72You can choose between the most compact guarenteed single-line format 91You can choose between the most compact guaranteed single-line format
73possible (nice for simple line-based protocols), a pure-ascii format 92possible (nice for simple line-based protocols), a pure-ascii format
74(for when your transport is not 8-bit clean, still supports the whole 93(for when your transport is not 8-bit clean, still supports the whole
75unicode range), or a pretty-printed format (for when you want to read that 94Unicode range), or a pretty-printed format (for when you want to read that
76stuff). Or you can combine those features in whatever way you like. 95stuff). Or you can combine those features in whatever way you like.
77 96
78=back 97=back
79 98
80=cut 99=cut
81 100
82package JSON::XS; 101package JSON::XS;
83 102
84use strict; 103use strict;
85 104
86our $VERSION = '1.4'; 105our $VERSION = '2.01';
87our @ISA = qw(Exporter); 106our @ISA = qw(Exporter);
88 107
89our @EXPORT = qw(to_json from_json); 108our @EXPORT = qw(encode_json decode_json to_json from_json);
109
110sub to_json($) {
111 require Carp;
112 Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
113}
114
115sub from_json($) {
116 require Carp;
117 Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
118}
90 119
91use Exporter; 120use Exporter;
92use XSLoader; 121use XSLoader;
93 122
94=head1 FUNCTIONAL INTERFACE 123=head1 FUNCTIONAL INTERFACE
95 124
96The following convinience methods are provided by this module. They are 125The following convenience methods are provided by this module. They are
97exported by default: 126exported by default:
98 127
99=over 4 128=over 4
100 129
101=item $json_text = to_json $perl_scalar 130=item $json_text = encode_json $perl_scalar
102 131
103Converts the given Perl data structure (a simple scalar or a reference to 132Converts the given Perl data structure to a UTF-8 encoded, binary string
104a hash or array) to a UTF-8 encoded, binary string (that is, the string contains 133(that is, the string contains octets only). Croaks on error.
105octets only). Croaks on error.
106 134
107This function call is functionally identical to: 135This function call is functionally identical to:
108 136
109 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 137 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
110 138
111except being faster. 139except being faster.
112 140
113=item $perl_scalar = from_json $json_text 141=item $perl_scalar = decode_json $json_text
114 142
115The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to 143The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
116parse that as an UTF-8 encoded JSON text, returning the resulting simple 144to parse that as an UTF-8 encoded JSON text, returning the resulting
117scalar or reference. Croaks on error. 145reference. Croaks on error.
118 146
119This function call is functionally identical to: 147This function call is functionally identical to:
120 148
121 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 149 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
122 150
132Perl. 160Perl.
133 161
134=back 162=back
135 163
136 164
165=head1 A FEW NOTES ON UNICODE AND PERL
166
167Since this often leads to confusion, here are a few very clear words on
168how Unicode works in Perl, modulo bugs.
169
170=over 4
171
172=item 1. Perl strings can store characters with ordinal values > 255.
173
174This enables you to store Unicode characters as single characters in a
175Perl string - very natural.
176
177=item 2. Perl does I<not> associate an encoding with your strings.
178
179Unless you force it to, e.g. when matching it against a regex, or printing
180the scalar to a file, in which case Perl either interprets your string as
181locale-encoded text, octets/binary, or as Unicode, depending on various
182settings. In no case is an encoding stored together with your data, it is
183I<use> that decides encoding, not any magical metadata.
184
185=item 3. The internal utf-8 flag has no meaning with regards to the
186encoding of your string.
187
188Just ignore that flag unless you debug a Perl bug, a module written in
189XS or want to dive into the internals of perl. Otherwise it will only
190confuse you, as, despite the name, it says nothing about how your string
191is encoded. You can have Unicode strings with that flag set, with that
192flag clear, and you can have binary data with that flag set and that flag
193clear. Other possibilities exist, too.
194
195If you didn't know about that flag, just the better, pretend it doesn't
196exist.
197
198=item 4. A "Unicode String" is simply a string where each character can be
199validly interpreted as a Unicode codepoint.
200
201If you have UTF-8 encoded data, it is no longer a Unicode string, but a
202Unicode string encoded in UTF-8, giving you a binary string.
203
204=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
205
206It's a fact. Learn to live with it.
207
208=back
209
210I hope this helps :)
211
212
137=head1 OBJECT-ORIENTED INTERFACE 213=head1 OBJECT-ORIENTED INTERFACE
138 214
139The object oriented interface lets you configure your own encoding or 215The object oriented interface lets you configure your own encoding or
140decoding style, within the limits of supported formats. 216decoding style, within the limits of supported formats.
141 217
152 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) 228 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
153 => {"a": [1, 2]} 229 => {"a": [1, 2]}
154 230
155=item $json = $json->ascii ([$enable]) 231=item $json = $json->ascii ([$enable])
156 232
233=item $enabled = $json->get_ascii
234
157If C<$enable> is true (or missing), then the C<encode> method will not 235If C<$enable> is true (or missing), then the C<encode> method will not
158generate characters outside the code range C<0..127> (which is ASCII). Any 236generate characters outside the code range C<0..127> (which is ASCII). Any
159unicode characters outside that range will be escaped using either a 237Unicode characters outside that range will be escaped using either a
160single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, 238single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
161as per RFC4627. The resulting encoded JSON text can be treated as a native 239as per RFC4627. The resulting encoded JSON text can be treated as a native
162unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string, 240Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
163or any other superset of ASCII. 241or any other superset of ASCII.
164 242
165If C<$enable> is false, then the C<encode> method will not escape Unicode 243If C<$enable> is false, then the C<encode> method will not escape Unicode
166characters unless required by the JSON syntax or other flags. This results 244characters unless required by the JSON syntax or other flags. This results
167in a faster and more compact format. 245in a faster and more compact format.
173 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 251 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
174 => ["\ud801\udc01"] 252 => ["\ud801\udc01"]
175 253
176=item $json = $json->latin1 ([$enable]) 254=item $json = $json->latin1 ([$enable])
177 255
256=item $enabled = $json->get_latin1
257
178If C<$enable> is true (or missing), then the C<encode> method will encode 258If C<$enable> is true (or missing), then the C<encode> method will encode
179the resulting JSON text as latin1 (or iso-8859-1), escaping any characters 259the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
180outside the code range C<0..255>. The resulting string can be treated as a 260outside the code range C<0..255>. The resulting string can be treated as a
181latin1-encoded JSON text or a native unicode string. The C<decode> method 261latin1-encoded JSON text or a native Unicode string. The C<decode> method
182will not be affected in any way by this flag, as C<decode> by default 262will not be affected in any way by this flag, as C<decode> by default
183expects unicode, which is a strict superset of latin1. 263expects Unicode, which is a strict superset of latin1.
184 264
185If C<$enable> is false, then the C<encode> method will not escape Unicode 265If C<$enable> is false, then the C<encode> method will not escape Unicode
186characters unless required by the JSON syntax or other flags. 266characters unless required by the JSON syntax or other flags.
187 267
188The main use for this flag is efficiently encoding binary data as JSON 268The main use for this flag is efficiently encoding binary data as JSON
189text, as most octets will not be escaped, resulting in a smaller encoded 269text, as most octets will not be escaped, resulting in a smaller encoded
190size. The disadvantage is that the resulting JSON text is encoded 270size. The disadvantage is that the resulting JSON text is encoded
191in latin1 (and must correctly be treated as such when storing and 271in latin1 (and must correctly be treated as such when storing and
192transfering), a rare encoding for JSON. It is therefore most useful when 272transferring), a rare encoding for JSON. It is therefore most useful when
193you want to store data structures known to contain binary data efficiently 273you want to store data structures known to contain binary data efficiently
194in files or databases, not when talking to other JSON encoders/decoders. 274in files or databases, not when talking to other JSON encoders/decoders.
195 275
196 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] 276 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
197 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) 277 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
198 278
199=item $json = $json->utf8 ([$enable]) 279=item $json = $json->utf8 ([$enable])
280
281=item $enabled = $json->get_utf8
200 282
201If C<$enable> is true (or missing), then the C<encode> method will encode 283If C<$enable> is true (or missing), then the C<encode> method will encode
202the JSON result into UTF-8, as required by many protocols, while the 284the JSON result into UTF-8, as required by many protocols, while the
203C<decode> method expects to be handled an UTF-8-encoded string. Please 285C<decode> method expects to be handled an UTF-8-encoded string. Please
204note that UTF-8-encoded strings do not contain any characters outside the 286note that UTF-8-encoded strings do not contain any characters outside the
205range C<0..255>, they are thus useful for bytewise/binary I/O. In future 287range C<0..255>, they are thus useful for bytewise/binary I/O. In future
206versions, enabling this option might enable autodetection of the UTF-16 288versions, enabling this option might enable autodetection of the UTF-16
207and UTF-32 encoding families, as described in RFC4627. 289and UTF-32 encoding families, as described in RFC4627.
208 290
209If C<$enable> is false, then the C<encode> method will return the JSON 291If C<$enable> is false, then the C<encode> method will return the JSON
210string as a (non-encoded) unicode string, while C<decode> expects thus a 292string as a (non-encoded) Unicode string, while C<decode> expects thus a
211unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs 293Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
212to be done yourself, e.g. using the Encode module. 294to be done yourself, e.g. using the Encode module.
213 295
214Example, output UTF-16BE-encoded JSON: 296Example, output UTF-16BE-encoded JSON:
215 297
216 use Encode; 298 use Encode;
238 ] 320 ]
239 } 321 }
240 322
241=item $json = $json->indent ([$enable]) 323=item $json = $json->indent ([$enable])
242 324
325=item $enabled = $json->get_indent
326
243If C<$enable> is true (or missing), then the C<encode> method will use a multiline 327If C<$enable> is true (or missing), then the C<encode> method will use a multiline
244format as output, putting every array member or object/hash key-value pair 328format as output, putting every array member or object/hash key-value pair
245into its own line, identing them properly. 329into its own line, indenting them properly.
246 330
247If C<$enable> is false, no newlines or indenting will be produced, and the 331If C<$enable> is false, no newlines or indenting will be produced, and the
248resulting JSON text is guarenteed not to contain any C<newlines>. 332resulting JSON text is guaranteed not to contain any C<newlines>.
249 333
250This setting has no effect when decoding JSON texts. 334This setting has no effect when decoding JSON texts.
251 335
252=item $json = $json->space_before ([$enable]) 336=item $json = $json->space_before ([$enable])
337
338=item $enabled = $json->get_space_before
253 339
254If C<$enable> is true (or missing), then the C<encode> method will add an extra 340If C<$enable> is true (or missing), then the C<encode> method will add an extra
255optional space before the C<:> separating keys from values in JSON objects. 341optional space before the C<:> separating keys from values in JSON objects.
256 342
257If C<$enable> is false, then the C<encode> method will not add any extra 343If C<$enable> is false, then the C<encode> method will not add any extra
263Example, space_before enabled, space_after and indent disabled: 349Example, space_before enabled, space_after and indent disabled:
264 350
265 {"key" :"value"} 351 {"key" :"value"}
266 352
267=item $json = $json->space_after ([$enable]) 353=item $json = $json->space_after ([$enable])
354
355=item $enabled = $json->get_space_after
268 356
269If C<$enable> is true (or missing), then the C<encode> method will add an extra 357If C<$enable> is true (or missing), then the C<encode> method will add an extra
270optional space after the C<:> separating keys from values in JSON objects 358optional space after the C<:> separating keys from values in JSON objects
271and extra whitespace after the C<,> separating key-value pairs and array 359and extra whitespace after the C<,> separating key-value pairs and array
272members. 360members.
278 366
279Example, space_before and indent disabled, space_after enabled: 367Example, space_before and indent disabled, space_after enabled:
280 368
281 {"key": "value"} 369 {"key": "value"}
282 370
371=item $json = $json->relaxed ([$enable])
372
373=item $enabled = $json->get_relaxed
374
375If C<$enable> is true (or missing), then C<decode> will accept some
376extensions to normal JSON syntax (see below). C<encode> will not be
377affected in anyway. I<Be aware that this option makes you accept invalid
378JSON texts as if they were valid!>. I suggest only to use this option to
379parse application-specific files written by humans (configuration files,
380resource files etc.)
381
382If C<$enable> is false (the default), then C<decode> will only accept
383valid JSON texts.
384
385Currently accepted extensions are:
386
387=over 4
388
389=item * list items can have an end-comma
390
391JSON I<separates> array elements and key-value pairs with commas. This
392can be annoying if you write JSON texts manually and want to be able to
393quickly append elements, so this extension accepts comma at the end of
394such items not just between them:
395
396 [
397 1,
398 2, <- this comma not normally allowed
399 ]
400 {
401 "k1": "v1",
402 "k2": "v2", <- this comma not normally allowed
403 }
404
405=item * shell-style '#'-comments
406
407Whenever JSON allows whitespace, shell-style comments are additionally
408allowed. They are terminated by the first carriage-return or line-feed
409character, after which more white-space and comments are allowed.
410
411 [
412 1, # this comment not allowed in JSON
413 # neither this one...
414 ]
415
416=back
417
283=item $json = $json->canonical ([$enable]) 418=item $json = $json->canonical ([$enable])
419
420=item $enabled = $json->get_canonical
284 421
285If C<$enable> is true (or missing), then the C<encode> method will output JSON objects 422If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
286by sorting their keys. This is adding a comparatively high overhead. 423by sorting their keys. This is adding a comparatively high overhead.
287 424
288If C<$enable> is false, then the C<encode> method will output key-value 425If C<$enable> is false, then the C<encode> method will output key-value
289pairs in the order Perl stores them (which will likely change between runs 426pairs in the order Perl stores them (which will likely change between runs
290of the same script). 427of the same script).
291 428
292This option is useful if you want the same data structure to be encoded as 429This option is useful if you want the same data structure to be encoded as
293the same JSON text (given the same overall settings). If it is disabled, 430the same JSON text (given the same overall settings). If it is disabled,
294the same hash migh be encoded differently even if contains the same data, 431the same hash might be encoded differently even if contains the same data,
295as key-value pairs have no inherent ordering in Perl. 432as key-value pairs have no inherent ordering in Perl.
296 433
297This setting has no effect when decoding JSON texts. 434This setting has no effect when decoding JSON texts.
298 435
299=item $json = $json->allow_nonref ([$enable]) 436=item $json = $json->allow_nonref ([$enable])
437
438=item $enabled = $json->get_allow_nonref
300 439
301If C<$enable> is true (or missing), then the C<encode> method can convert a 440If C<$enable> is true (or missing), then the C<encode> method can convert a
302non-reference into its corresponding string, number or null JSON value, 441non-reference into its corresponding string, number or null JSON value,
303which is an extension to RFC4627. Likewise, C<decode> will accept those JSON 442which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
304values instead of croaking. 443values instead of croaking.
314 JSON::XS->new->allow_nonref->encode ("Hello, World!") 453 JSON::XS->new->allow_nonref->encode ("Hello, World!")
315 => "Hello, World!" 454 => "Hello, World!"
316 455
317=item $json = $json->allow_blessed ([$enable]) 456=item $json = $json->allow_blessed ([$enable])
318 457
458=item $enabled = $json->get_allow_blessed
459
319If C<$enable> is true (or missing), then the C<encode> method will not 460If C<$enable> is true (or missing), then the C<encode> method will not
320barf when it encounters a blessed reference. Instead, the value of the 461barf when it encounters a blessed reference. Instead, the value of the
321B<convert_blessed> option will decide wether C<null> (C<convert_blessed> 462B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
322disabled or no C<to_json> method found) or a representation of the 463disabled or no C<TO_JSON> method found) or a representation of the
323object (C<convert_blessed> enabled and C<to_json> method found) is being 464object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
324encoded. Has no effect on C<decode>. 465encoded. Has no effect on C<decode>.
325 466
326If C<$enable> is false (the default), then C<encode> will throw an 467If C<$enable> is false (the default), then C<encode> will throw an
327exception when it encounters a blessed object. 468exception when it encounters a blessed object.
328 469
329=item $json = $json->convert_blessed ([$enable]) 470=item $json = $json->convert_blessed ([$enable])
471
472=item $enabled = $json->get_convert_blessed
330 473
331If C<$enable> is true (or missing), then C<encode>, upon encountering a 474If C<$enable> is true (or missing), then C<encode>, upon encountering a
332blessed object, will check for the availability of the C<TO_JSON> method 475blessed object, will check for the availability of the C<TO_JSON> method
333on the object's class. If found, it will be called in scalar context 476on the object's class. If found, it will be called in scalar context
334and the resulting scalar will be encoded instead of the object. If no 477and the resulting scalar will be encoded instead of the object. If no
338The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON> 481The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
339returns other blessed objects, those will be handled in the same 482returns other blessed objects, those will be handled in the same
340way. C<TO_JSON> must take care of not causing an endless recursion cycle 483way. C<TO_JSON> must take care of not causing an endless recursion cycle
341(== crash) in this case. The name of C<TO_JSON> was chosen because other 484(== crash) in this case. The name of C<TO_JSON> was chosen because other
342methods called by the Perl core (== not by the user of the object) are 485methods called by the Perl core (== not by the user of the object) are
343usually in upper case letters and to avoid collisions with the C<to_json> 486usually in upper case letters and to avoid collisions with any C<to_json>
344function. 487function or method.
345 488
346This setting does not yet influence C<decode> in any way, but in the 489This setting does not yet influence C<decode> in any way, but in the
347future, global hooks might get installed that influence C<decode> and are 490future, global hooks might get installed that influence C<decode> and are
348enabled by this setting. 491enabled by this setting.
349 492
350If C<$enable> is false, then the C<allow_blessed> setting will decide what 493If C<$enable> is false, then the C<allow_blessed> setting will decide what
351to do when a blessed object is found. 494to do when a blessed object is found.
352 495
496=item $json = $json->filter_json_object ([$coderef->($hashref)])
497
498When C<$coderef> is specified, it will be called from C<decode> each
499time it decodes a JSON object. The only argument is a reference to the
500newly-created hash. If the code references returns a single scalar (which
501need not be a reference), this value (i.e. a copy of that scalar to avoid
502aliasing) is inserted into the deserialised data structure. If it returns
503an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
504original deserialised hash will be inserted. This setting can slow down
505decoding considerably.
506
507When C<$coderef> is omitted or undefined, any existing callback will
508be removed and C<decode> will not change the deserialised hash in any
509way.
510
511Example, convert all JSON objects into the integer 5:
512
513 my $js = JSON::XS->new->filter_json_object (sub { 5 });
514 # returns [5]
515 $js->decode ('[{}]')
516 # throw an exception because allow_nonref is not enabled
517 # so a lone 5 is not allowed.
518 $js->decode ('{"a":1, "b":2}');
519
520=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
521
522Works remotely similar to C<filter_json_object>, but is only called for
523JSON objects having a single key named C<$key>.
524
525This C<$coderef> is called before the one specified via
526C<filter_json_object>, if any. It gets passed the single value in the JSON
527object. If it returns a single value, it will be inserted into the data
528structure. If it returns nothing (not even C<undef> but the empty list),
529the callback from C<filter_json_object> will be called next, as if no
530single-key callback were specified.
531
532If C<$coderef> is omitted or undefined, the corresponding callback will be
533disabled. There can only ever be one callback for a given key.
534
535As this callback gets called less often then the C<filter_json_object>
536one, decoding speed will not usually suffer as much. Therefore, single-key
537objects make excellent targets to serialise Perl objects into, especially
538as single-key JSON objects are as close to the type-tagged value concept
539as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
540support this in any way, so you need to make sure your data never looks
541like a serialised Perl hash.
542
543Typical names for the single object key are C<__class_whatever__>, or
544C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
545things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
546with real hashes.
547
548Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
549into the corresponding C<< $WIDGET{<id>} >> object:
550
551 # return whatever is in $WIDGET{5}:
552 JSON::XS
553 ->new
554 ->filter_json_single_key_object (__widget__ => sub {
555 $WIDGET{ $_[0] }
556 })
557 ->decode ('{"__widget__": 5')
558
559 # this can be used with a TO_JSON method in some "widget" class
560 # for serialisation to json:
561 sub WidgetBase::TO_JSON {
562 my ($self) = @_;
563
564 unless ($self->{id}) {
565 $self->{id} = ..get..some..id..;
566 $WIDGET{$self->{id}} = $self;
567 }
568
569 { __widget__ => $self->{id} }
570 }
571
353=item $json = $json->shrink ([$enable]) 572=item $json = $json->shrink ([$enable])
573
574=item $enabled = $json->get_shrink
354 575
355Perl usually over-allocates memory a bit when allocating space for 576Perl usually over-allocates memory a bit when allocating space for
356strings. This flag optionally resizes strings generated by either 577strings. This flag optionally resizes strings generated by either
357C<encode> or C<decode> to their minimum size possible. This can save 578C<encode> or C<decode> to their minimum size possible. This can save
358memory when your JSON texts are either very very long or you have many 579memory when your JSON texts are either very very long or you have many
376strings that look like integers or floats into integers or floats 597strings that look like integers or floats into integers or floats
377internally (there is no difference on the Perl level), saving space. 598internally (there is no difference on the Perl level), saving space.
378 599
379=item $json = $json->max_depth ([$maximum_nesting_depth]) 600=item $json = $json->max_depth ([$maximum_nesting_depth])
380 601
602=item $max_depth = $json->get_max_depth
603
381Sets the maximum nesting level (default C<512>) accepted while encoding 604Sets the maximum nesting level (default C<512>) accepted while encoding
382or decoding. If the JSON text or Perl data structure has an equal or 605or decoding. If the JSON text or Perl data structure has an equal or
383higher nesting level then this limit, then the encoder and decoder will 606higher nesting level then this limit, then the encoder and decoder will
384stop and croak at that point. 607stop and croak at that point.
385 608
396used, which is rarely useful. 619used, which is rarely useful.
397 620
398See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 621See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
399 622
400=item $json = $json->max_size ([$maximum_string_size]) 623=item $json = $json->max_size ([$maximum_string_size])
624
625=item $max_size = $json->get_max_size
401 626
402Set the maximum length a JSON text may have (in bytes) where decoding is 627Set the maximum length a JSON text may have (in bytes) where decoding is
403being attempted. The default is C<0>, meaning no limit. When C<decode> 628being attempted. The default is C<0>, meaning no limit. When C<decode>
404is called on a string longer then this number of characters it will not 629is called on a string longer then this number of characters it will not
405attempt to decode the string but throw an exception. This setting has no 630attempt to decode the string but throw an exception. This setting has no
452vice versa. These mappings are designed to "do the right thing" in most 677vice versa. These mappings are designed to "do the right thing" in most
453circumstances automatically, preserving round-tripping characteristics 678circumstances automatically, preserving round-tripping characteristics
454(what you put in comes out as something equivalent). 679(what you put in comes out as something equivalent).
455 680
456For the more enlightened: note that in the following descriptions, 681For the more enlightened: note that in the following descriptions,
457lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl> 682lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
458refers to the abstract Perl language itself. 683refers to the abstract Perl language itself.
459 684
460 685
461=head2 JSON -> PERL 686=head2 JSON -> PERL
462 687
463=over 4 688=over 4
464 689
465=item object 690=item object
466 691
467A JSON object becomes a reference to a hash in Perl. No ordering of object 692A JSON object becomes a reference to a hash in Perl. No ordering of object
468keys is preserved (JSON does not preserver object key ordering itself). 693keys is preserved (JSON does not preserve object key ordering itself).
469 694
470=item array 695=item array
471 696
472A JSON array becomes a reference to an array in Perl. 697A JSON array becomes a reference to an array in Perl.
473 698
477are represented by the same codepoints in the Perl string, so no manual 702are represented by the same codepoints in the Perl string, so no manual
478decoding is necessary. 703decoding is necessary.
479 704
480=item number 705=item number
481 706
482A JSON number becomes either an integer or numeric (floating point) 707A JSON number becomes either an integer, numeric (floating point) or
483scalar in perl, depending on its range and any fractional parts. On the 708string scalar in perl, depending on its range and any fractional parts. On
484Perl level, there is no difference between those as Perl handles all the 709the Perl level, there is no difference between those as Perl handles all
485conversion details, but an integer may take slightly less memory and might 710the conversion details, but an integer may take slightly less memory and
486represent more values exactly than (floating point) numbers. 711might represent more values exactly than (floating point) numbers.
712
713If the number consists of digits only, JSON::XS will try to represent
714it as an integer value. If that fails, it will try to represent it as
715a numeric (floating point) value if that is possible without loss of
716precision. Otherwise it will preserve the number as a string value.
717
718Numbers containing a fractional or exponential part will always be
719represented as numeric (floating point) values, possibly at a loss of
720precision.
721
722This might create round-tripping problems as numbers might become strings,
723but as Perl is typeless there is no other way to do it.
487 724
488=item true, false 725=item true, false
489 726
490These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, 727These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
491respectively. They are overloaded to act almost exactly like the numbers 728respectively. They are overloaded to act almost exactly like the numbers
492C<1> and C<0>. You can check wether a scalar is a JSON boolean by using 729C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
493the C<JSON::XS::is_bool> function. 730the C<JSON::XS::is_bool> function.
494 731
495=item null 732=item null
496 733
497A JSON null atom becomes C<undef> in Perl. 734A JSON null atom becomes C<undef> in Perl.
528Other unblessed references are generally not allowed and will cause an 765Other unblessed references are generally not allowed and will cause an
529exception to be thrown, except for references to the integers C<0> and 766exception to be thrown, except for references to the integers C<0> and
530C<1>, which get turned into C<false> and C<true> atoms in JSON. You can 767C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
531also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. 768also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
532 769
533 to_json [\0,JSON::XS::true] # yields [false,true] 770 encode_json [\0,JSON::XS::true] # yields [false,true]
534 771
535=item JSON::XS::true, JSON::XS::false 772=item JSON::XS::true, JSON::XS::false
536 773
537These special values become JSON true and JSON false values, 774These special values become JSON true and JSON false values,
538respectively. You cna alos use C<\1> and C<\0> directly if you want. 775respectively. You can also use C<\1> and C<\0> directly if you want.
539 776
540=item blessed objects 777=item blessed objects
541 778
542Blessed objects are not allowed. JSON::XS currently tries to encode their 779Blessed objects are not allowed. JSON::XS currently tries to encode their
543underlying representation (hash- or arrayref), but this behaviour might 780underlying representation (hash- or arrayref), but this behaviour might
549difficult objects to encode: JSON::XS will encode undefined scalars as 786difficult objects to encode: JSON::XS will encode undefined scalars as
550JSON null value, scalars that have last been used in a string context 787JSON null value, scalars that have last been used in a string context
551before encoding as JSON strings and anything else as number value: 788before encoding as JSON strings and anything else as number value:
552 789
553 # dump as number 790 # dump as number
554 to_json [2] # yields [2] 791 encode_json [2] # yields [2]
555 to_json [-3.0e17] # yields [-3e+17] 792 encode_json [-3.0e17] # yields [-3e+17]
556 my $value = 5; to_json [$value] # yields [5] 793 my $value = 5; encode_json [$value] # yields [5]
557 794
558 # used as string, so dump as string 795 # used as string, so dump as string
559 print $value; 796 print $value;
560 to_json [$value] # yields ["5"] 797 encode_json [$value] # yields ["5"]
561 798
562 # undef becomes null 799 # undef becomes null
563 to_json [undef] # yields [null] 800 encode_json [undef] # yields [null]
564 801
565You can force the type to be a string by stringifying it: 802You can force the type to be a JSON string by stringifying it:
566 803
567 my $x = 3.1; # some variable containing a number 804 my $x = 3.1; # some variable containing a number
568 "$x"; # stringified 805 "$x"; # stringified
569 $x .= ""; # another, more awkward way to stringify 806 $x .= ""; # another, more awkward way to stringify
570 print $x; # perl does it for you, too, quite often 807 print $x; # perl does it for you, too, quite often
571 808
572You can force the type to be a number by numifying it: 809You can force the type to be a JSON number by numifying it:
573 810
574 my $x = "3"; # some variable containing a string 811 my $x = "3"; # some variable containing a string
575 $x += 0; # numify it, ensuring it will be dumped as a number 812 $x += 0; # numify it, ensuring it will be dumped as a number
576 $x *= 1; # same thing, the choise is yours. 813 $x *= 1; # same thing, the choice is yours.
577 814
578You can not currently output JSON booleans or force the type in other, 815You can not currently force the type in other, less obscure, ways. Tell me
579less obscure, ways. Tell me if you need this capability. 816if you need this capability.
580 817
581=back 818=back
582 819
583 820
584=head1 COMPARISON 821=head1 COMPARISON
593 830
594=item JSON 1.07 831=item JSON 1.07
595 832
596Slow (but very portable, as it is written in pure Perl). 833Slow (but very portable, as it is written in pure Perl).
597 834
598Undocumented/buggy Unicode handling (how JSON handles unicode values is 835Undocumented/buggy Unicode handling (how JSON handles Unicode values is
599undocumented. One can get far by feeding it unicode strings and doing 836undocumented. One can get far by feeding it Unicode strings and doing
600en-/decoding oneself, but unicode escapes are not working properly). 837en-/decoding oneself, but Unicode escapes are not working properly).
601 838
602No roundtripping (strings get clobbered if they look like numbers, e.g. 839No round-tripping (strings get clobbered if they look like numbers, e.g.
603the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will 840the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
604decode into the number 2. 841decode into the number 2.
605 842
606=item JSON::PC 0.01 843=item JSON::PC 0.01
607 844
608Very fast. 845Very fast.
609 846
610Undocumented/buggy Unicode handling. 847Undocumented/buggy Unicode handling.
611 848
612No roundtripping. 849No round-tripping.
613 850
614Has problems handling many Perl values (e.g. regex results and other magic 851Has problems handling many Perl values (e.g. regex results and other magic
615values will make it croak). 852values will make it croak).
616 853
617Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> 854Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
627Very inflexible (no human-readable format supported, format pretty much 864Very inflexible (no human-readable format supported, format pretty much
628undocumented. I need at least a format for easy reading by humans and a 865undocumented. I need at least a format for easy reading by humans and a
629single-line compact format for use in a protocol, and preferably a way to 866single-line compact format for use in a protocol, and preferably a way to
630generate ASCII-only JSON texts). 867generate ASCII-only JSON texts).
631 868
632Completely broken (and confusingly documented) Unicode handling (unicode 869Completely broken (and confusingly documented) Unicode handling (Unicode
633escapes are not working properly, you need to set ImplicitUnicode to 870escapes are not working properly, you need to set ImplicitUnicode to
634I<different> values on en- and decoding to get symmetric behaviour). 871I<different> values on en- and decoding to get symmetric behaviour).
635 872
636No roundtripping (simple cases work, but this depends on wether the scalar 873No round-tripping (simple cases work, but this depends on whether the scalar
637value was used in a numeric context or not). 874value was used in a numeric context or not).
638 875
639Dumping hashes may skip hash values depending on iterator state. 876Dumping hashes may skip hash values depending on iterator state.
640 877
641Unmaintained (maintainer unresponsive for many months, bugs are not 878Unmaintained (maintainer unresponsive for many months, bugs are not
642getting fixed). 879getting fixed).
643 880
644Does not check input for validity (i.e. will accept non-JSON input and 881Does not check input for validity (i.e. will accept non-JSON input and
645return "something" instead of raising an exception. This is a security 882return "something" instead of raising an exception. This is a security
646issue: imagine two banks transfering money between each other using 883issue: imagine two banks transferring money between each other using
647JSON. One bank might parse a given non-JSON request and deduct money, 884JSON. One bank might parse a given non-JSON request and deduct money,
648while the other might reject the transaction with a syntax error. While a 885while the other might reject the transaction with a syntax error. While a
649good protocol will at least recover, that is extra unnecessary work and 886good protocol will at least recover, that is extra unnecessary work and
650the transaction will still not succeed). 887the transaction will still not succeed).
651 888
652=item JSON::DWIW 0.04 889=item JSON::DWIW 0.04
653 890
654Very fast. Very natural. Very nice. 891Very fast. Very natural. Very nice.
655 892
656Undocumented unicode handling (but the best of the pack. Unicode escapes 893Undocumented Unicode handling (but the best of the pack. Unicode escapes
657still don't get parsed properly). 894still don't get parsed properly).
658 895
659Very inflexible. 896Very inflexible.
660 897
661No roundtripping. 898No round-tripping.
662 899
663Does not generate valid JSON texts (key strings are often unquoted, empty keys 900Does not generate valid JSON texts (key strings are often unquoted, empty keys
664result in nothing being output) 901result in nothing being output)
665 902
666Does not check input for validity. 903Does not check input for validity.
681 my $yaml = $to_yaml->encode ($ref) . "\n"; 918 my $yaml = $to_yaml->encode ($ref) . "\n";
682 919
683This will usually generate JSON texts that also parse as valid 920This will usually generate JSON texts that also parse as valid
684YAML. Please note that YAML has hardcoded limits on (simple) object key 921YAML. Please note that YAML has hardcoded limits on (simple) object key
685lengths that JSON doesn't have, so you should make sure that your hash 922lengths that JSON doesn't have, so you should make sure that your hash
686keys are noticably shorter than the 1024 characters YAML allows. 923keys are noticeably shorter than the 1024 characters YAML allows.
687 924
688There might be other incompatibilities that I am not aware of. In general 925There might be other incompatibilities that I am not aware of. In general
689you should not try to generate YAML with a JSON generator or vice versa, 926you should not try to generate YAML with a JSON generator or vice versa,
690or try to parse JSON with a YAML parser or vice versa: chances are high 927or try to parse JSON with a YAML parser or vice versa: chances are high
691that you will run into severe interoperability problems. 928that you will run into severe interoperability problems.
707It shows the number of encodes/decodes per second (JSON::XS uses 944It shows the number of encodes/decodes per second (JSON::XS uses
708the functional interface, while JSON::XS/2 uses the OO interface 945the functional interface, while JSON::XS/2 uses the OO interface
709with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables 946with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
710shrink). Higher is better: 947shrink). Higher is better:
711 948
712 Storable | 15779.925 | 14169.946 |
713 -----------+------------+------------+
714 module | encode | decode | 949 module | encode | decode |
715 -----------|------------|------------| 950 -----------|------------|------------|
716 JSON | 4990.842 | 4088.813 | 951 JSON 1.x | 4990.842 | 4088.813 |
717 JSON::DWIW | 51653.990 | 71575.154 | 952 JSON::DWIW | 51653.990 | 71575.154 |
718 JSON::PC | 65948.176 | 74631.744 | 953 JSON::PC | 65948.176 | 74631.744 |
719 JSON::PP | 8931.652 | 3817.168 | 954 JSON::PP | 8931.652 | 3817.168 |
720 JSON::Syck | 24877.248 | 27776.848 | 955 JSON::Syck | 24877.248 | 27776.848 |
721 JSON::XS | 388361.481 | 227951.304 | 956 JSON::XS | 388361.481 | 227951.304 |
723 JSON::XS/3 | 338250.323 | 218453.333 | 958 JSON::XS/3 | 338250.323 | 218453.333 |
724 Storable | 16500.016 | 135300.129 | 959 Storable | 16500.016 | 135300.129 |
725 -----------+------------+------------+ 960 -----------+------------+------------+
726 961
727That is, JSON::XS is about five times faster than JSON::DWIW on encoding, 962That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
728about three times faster on decoding, and over fourty times faster 963about three times faster on decoding, and over forty times faster
729than JSON, even with pretty-printing and key sorting. It also compares 964than JSON, even with pretty-printing and key sorting. It also compares
730favourably to Storable for small amounts of data. 965favourably to Storable for small amounts of data.
731 966
732Using a longer test string (roughly 18KB, generated from Yahoo! Locals 967Using a longer test string (roughly 18KB, generated from Yahoo! Locals
733search API (http://nanoref.com/yahooapis/mgPdGg): 968search API (http://nanoref.com/yahooapis/mgPdGg):
734 969
735 module | encode | decode | 970 module | encode | decode |
736 -----------|------------|------------| 971 -----------|------------|------------|
737 JSON | 55.260 | 34.971 | 972 JSON 1.x | 55.260 | 34.971 |
738 JSON::DWIW | 825.228 | 1082.513 | 973 JSON::DWIW | 825.228 | 1082.513 |
739 JSON::PC | 3571.444 | 2394.829 | 974 JSON::PC | 3571.444 | 2394.829 |
740 JSON::PP | 210.987 | 32.574 | 975 JSON::PP | 210.987 | 32.574 |
741 JSON::Syck | 552.551 | 787.544 | 976 JSON::Syck | 552.551 | 787.544 |
742 JSON::XS | 5780.463 | 4854.519 | 977 JSON::XS | 5780.463 | 4854.519 |
746 -----------+------------+------------+ 981 -----------+------------+------------+
747 982
748Again, JSON::XS leads by far (except for Storable which non-surprisingly 983Again, JSON::XS leads by far (except for Storable which non-surprisingly
749decodes faster). 984decodes faster).
750 985
751On large strings containing lots of high unicode characters, some modules 986On large strings containing lots of high Unicode characters, some modules
752(such as JSON::PC) seem to decode faster than JSON::XS, but the result 987(such as JSON::PC) seem to decode faster than JSON::XS, but the result
753will be broken due to missing (or wrong) unicode handling. Others refuse 988will be broken due to missing (or wrong) Unicode handling. Others refuse
754to decode or encode properly, so it was impossible to prepare a fair 989to decode or encode properly, so it was impossible to prepare a fair
755comparison table for that case. 990comparison table for that case.
756 991
757 992
758=head1 SECURITY CONSIDERATIONS 993=head1 SECURITY CONSIDERATIONS
764any buffer overflows. Obviously, this module should ensure that and I am 999any buffer overflows. Obviously, this module should ensure that and I am
765trying hard on making that true, but you never know. 1000trying hard on making that true, but you never know.
766 1001
767Second, you need to avoid resource-starving attacks. That means you should 1002Second, you need to avoid resource-starving attacks. That means you should
768limit the size of JSON texts you accept, or make sure then when your 1003limit the size of JSON texts you accept, or make sure then when your
769resources run out, thats just fine (e.g. by using a separate process that 1004resources run out, that's just fine (e.g. by using a separate process that
770can crash safely). The size of a JSON text in octets or characters is 1005can crash safely). The size of a JSON text in octets or characters is
771usually a good indication of the size of the resources required to decode 1006usually a good indication of the size of the resources required to decode
772it into a Perl structure. While JSON::XS can check the size of the JSON 1007it into a Perl structure. While JSON::XS can check the size of the JSON
773text, it might be too late when you already have it in memory, so you 1008text, it might be too late when you already have it in memory, so you
774might want to check the size before you accept the string. 1009might want to check the size before you accept the string.
785And last but least, something else could bomb you that I forgot to think 1020And last but least, something else could bomb you that I forgot to think
786of. In that case, you get to keep the pieces. I am always open for hints, 1021of. In that case, you get to keep the pieces. I am always open for hints,
787though... 1022though...
788 1023
789If you are using JSON::XS to return packets to consumption 1024If you are using JSON::XS to return packets to consumption
790by javascript scripts in a browser you should have a look at 1025by JavaScript scripts in a browser you should have a look at
791L<http://jpsykes.com/47/practical-csrf-and-json-security> to see wether 1026L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
792you are vulnerable to some common attack vectors (which really are browser 1027you are vulnerable to some common attack vectors (which really are browser
793design bugs, but it is still you who will have to deal with it, as major 1028design bugs, but it is still you who will have to deal with it, as major
794browser developers care only for features, not about doing security 1029browser developers care only for features, not about doing security
795right). 1030right).
796 1031
797 1032
1033=head1 THREADS
1034
1035This module is I<not> guaranteed to be thread safe and there are no
1036plans to change this until Perl gets thread support (as opposed to the
1037horribly slow so-called "threads" which are simply slow and bloated
1038process simulations - use fork, its I<much> faster, cheaper, better).
1039
1040(It might actually work, but you have been warned).
1041
1042
798=head1 BUGS 1043=head1 BUGS
799 1044
800While the goal of this module is to be correct, that unfortunately does 1045While the goal of this module is to be correct, that unfortunately does
801not mean its bug-free, only that I think its design is bug-free. It is 1046not mean its bug-free, only that I think its design is bug-free. It is
802still relatively early in its development. If you keep reporting bugs they 1047still relatively early in its development. If you keep reporting bugs they
803will be fixed swiftly, though. 1048will be fixed swiftly, though.
804 1049
1050Please refrain from using rt.cpan.org or any other bug reporting
1051service. I put the contact address into my modules for a reason.
1052
805=cut 1053=cut
806 1054
807our $true = do { bless \(my $dummy = "1"), "JSON::XS::Boolean" }; 1055our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
808our $false = do { bless \(my $dummy = "0"), "JSON::XS::Boolean" }; 1056our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
809 1057
810sub true() { $true } 1058sub true() { $true }
811sub false() { $false } 1059sub false() { $false }
812 1060
813sub is_bool($) { 1061sub is_bool($) {

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