ViewVC Help
View File | Revision Log | Show Annotations | Download File
/cvs/JSON-XS/XS.pm
(Generate patch)

Comparing JSON-XS/XS.pm (file contents):
Revision 1.45 by root, Mon Jun 25 04:16:46 2007 UTC vs.
Revision 1.109 by root, Sat Jul 19 04:21:32 2008 UTC

1=head1 NAME 1=head1 NAME
2 2
3JSON::XS - JSON serialising/deserialising, done correctly and fast 3JSON::XS - JSON serialising/deserialising, done correctly and fast
4
5=encoding utf-8
6
7JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
8 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
4 9
5=head1 SYNOPSIS 10=head1 SYNOPSIS
6 11
7 use JSON::XS; 12 use JSON::XS;
8 13
9 # exported functions, they croak on error 14 # exported functions, they croak on error
10 # and expect/generate UTF-8 15 # and expect/generate UTF-8
11 16
12 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 17 $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
13 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 18 $perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
14
15 # objToJson and jsonToObj aliases to to_json and from_json
16 # are exported for compatibility to the JSON module,
17 # but should not be used in new code.
18 19
19 # OO-interface 20 # OO-interface
20 21
21 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 22 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
22 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 23 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
23 $perl_scalar = $coder->decode ($unicode_json_text); 24 $perl_scalar = $coder->decode ($unicode_json_text);
24 25
26 # Note that JSON version 2.0 and above will automatically use JSON::XS
27 # if available, at virtually no speed overhead either, so you should
28 # be able to just:
29
30 use JSON;
31
32 # and do the same things, except that you have a pure-perl fallback now.
33
25=head1 DESCRIPTION 34=head1 DESCRIPTION
26 35
27This module converts Perl data structures to JSON and vice versa. Its 36This module converts Perl data structures to JSON and vice versa. Its
28primary goal is to be I<correct> and its secondary goal is to be 37primary goal is to be I<correct> and its secondary goal is to be
29I<fast>. To reach the latter goal it was written in C. 38I<fast>. To reach the latter goal it was written in C.
39
40Beginning with version 2.0 of the JSON module, when both JSON and
41JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
42overridden) with no overhead due to emulation (by inheriting constructor
43and methods). If JSON::XS is not available, it will fall back to the
44compatible JSON::PP module as backend, so using JSON instead of JSON::XS
45gives you a portable JSON API that can be fast when you need and doesn't
46require a C compiler when that is a problem.
30 47
31As this is the n-th-something JSON module on CPAN, what was the reason 48As this is the n-th-something JSON module on CPAN, what was the reason
32to write yet another JSON module? While it seems there are many JSON 49to write yet another JSON module? While it seems there are many JSON
33modules, none of them correctly handle all corner cases, and in most cases 50modules, none of them correctly handle all corner cases, and in most cases
34their maintainers are unresponsive, gone missing, or not listening to bug 51their maintainers are unresponsive, gone missing, or not listening to bug
41 58
42=head2 FEATURES 59=head2 FEATURES
43 60
44=over 4 61=over 4
45 62
46=item * correct unicode handling 63=item * correct Unicode handling
47 64
48This module knows how to handle Unicode, and even documents how and when 65This module knows how to handle Unicode, documents how and when it does
49it does so. 66so, and even documents what "correct" means.
50 67
51=item * round-trip integrity 68=item * round-trip integrity
52 69
53When you serialise a perl data structure using only datatypes supported 70When you serialise a perl data structure using only data types supported
54by JSON, the deserialised data structure is identical on the Perl level. 71by JSON, the deserialised data structure is identical on the Perl level.
55(e.g. the string "2.0" doesn't suddenly become "2" just because it looks 72(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
56like a number). 73like a number). There minor I<are> exceptions to this, read the MAPPING
74section below to learn about those.
57 75
58=item * strict checking of JSON correctness 76=item * strict checking of JSON correctness
59 77
60There is no guessing, no generating of illegal JSON texts by default, 78There is no guessing, no generating of illegal JSON texts by default,
61and only JSON is accepted as input by default (the latter is a security 79and only JSON is accepted as input by default (the latter is a security
62feature). 80feature).
63 81
64=item * fast 82=item * fast
65 83
66Compared to other JSON modules, this module compares favourably in terms 84Compared to other JSON modules and other serialisers such as Storable,
67of speed, too. 85this module usually compares favourably in terms of speed, too.
68 86
69=item * simple to use 87=item * simple to use
70 88
71This module has both a simple functional interface as well as an OO 89This module has both a simple functional interface as well as an object
72interface. 90oriented interface interface.
73 91
74=item * reasonably versatile output formats 92=item * reasonably versatile output formats
75 93
76You can choose between the most compact guarenteed single-line format 94You can choose between the most compact guaranteed-single-line format
77possible (nice for simple line-based protocols), a pure-ascii format 95possible (nice for simple line-based protocols), a pure-ASCII format
78(for when your transport is not 8-bit clean, still supports the whole 96(for when your transport is not 8-bit clean, still supports the whole
79unicode range), or a pretty-printed format (for when you want to read that 97Unicode range), or a pretty-printed format (for when you want to read that
80stuff). Or you can combine those features in whatever way you like. 98stuff). Or you can combine those features in whatever way you like.
81 99
82=back 100=back
83 101
84=cut 102=cut
85 103
86package JSON::XS; 104package JSON::XS;
87 105
88use strict; 106use strict;
89 107
90our $VERSION = '1.4'; 108our $VERSION = '2.222';
91our @ISA = qw(Exporter); 109our @ISA = qw(Exporter);
92 110
93our @EXPORT = qw(to_json from_json objToJson jsonToObj); 111our @EXPORT = qw(encode_json decode_json to_json from_json);
112
113sub to_json($) {
114 require Carp;
115 Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
116}
117
118sub from_json($) {
119 require Carp;
120 Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
121}
94 122
95use Exporter; 123use Exporter;
96use XSLoader; 124use XSLoader;
97 125
98=head1 FUNCTIONAL INTERFACE 126=head1 FUNCTIONAL INTERFACE
99 127
100The following convinience methods are provided by this module. They are 128The following convenience methods are provided by this module. They are
101exported by default: 129exported by default:
102 130
103=over 4 131=over 4
104 132
105=item $json_text = to_json $perl_scalar 133=item $json_text = encode_json $perl_scalar
106 134
107Converts the given Perl data structure (a simple scalar or a reference to 135Converts the given Perl data structure to a UTF-8 encoded, binary string
108a hash or array) to a UTF-8 encoded, binary string (that is, the string contains 136(that is, the string contains octets only). Croaks on error.
109octets only). Croaks on error.
110 137
111This function call is functionally identical to: 138This function call is functionally identical to:
112 139
113 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 140 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
114 141
115except being faster. 142Except being faster.
116 143
117=item $perl_scalar = from_json $json_text 144=item $perl_scalar = decode_json $json_text
118 145
119The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to 146The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
120parse that as an UTF-8 encoded JSON text, returning the resulting simple 147to parse that as an UTF-8 encoded JSON text, returning the resulting
121scalar or reference. Croaks on error. 148reference. Croaks on error.
122 149
123This function call is functionally identical to: 150This function call is functionally identical to:
124 151
125 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 152 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
126 153
127except being faster. 154Except being faster.
128 155
129=item $is_boolean = JSON::XS::is_bool $scalar 156=item $is_boolean = JSON::XS::is_bool $scalar
130 157
131Returns true if the passed scalar represents either JSON::XS::true or 158Returns 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 159JSON::XS::false, two constants that act like C<1> and C<0>, respectively
136Perl. 163Perl.
137 164
138=back 165=back
139 166
140 167
168=head1 A FEW NOTES ON UNICODE AND PERL
169
170Since this often leads to confusion, here are a few very clear words on
171how Unicode works in Perl, modulo bugs.
172
173=over 4
174
175=item 1. Perl strings can store characters with ordinal values > 255.
176
177This enables you to store Unicode characters as single characters in a
178Perl string - very natural.
179
180=item 2. Perl does I<not> associate an encoding with your strings.
181
182... until you force it to, e.g. when matching it against a regex, or
183printing the scalar to a file, in which case Perl either interprets your
184string as locale-encoded text, octets/binary, or as Unicode, depending
185on various settings. In no case is an encoding stored together with your
186data, it is I<use> that decides encoding, not any magical meta data.
187
188=item 3. The internal utf-8 flag has no meaning with regards to the
189encoding of your string.
190
191Just ignore that flag unless you debug a Perl bug, a module written in
192XS or want to dive into the internals of perl. Otherwise it will only
193confuse you, as, despite the name, it says nothing about how your string
194is encoded. You can have Unicode strings with that flag set, with that
195flag clear, and you can have binary data with that flag set and that flag
196clear. Other possibilities exist, too.
197
198If you didn't know about that flag, just the better, pretend it doesn't
199exist.
200
201=item 4. A "Unicode String" is simply a string where each character can be
202validly interpreted as a Unicode code point.
203
204If you have UTF-8 encoded data, it is no longer a Unicode string, but a
205Unicode string encoded in UTF-8, giving you a binary string.
206
207=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
208
209It's a fact. Learn to live with it.
210
211=back
212
213I hope this helps :)
214
215
141=head1 OBJECT-ORIENTED INTERFACE 216=head1 OBJECT-ORIENTED INTERFACE
142 217
143The object oriented interface lets you configure your own encoding or 218The object oriented interface lets you configure your own encoding or
144decoding style, within the limits of supported formats. 219decoding style, within the limits of supported formats.
145 220
156 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) 231 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
157 => {"a": [1, 2]} 232 => {"a": [1, 2]}
158 233
159=item $json = $json->ascii ([$enable]) 234=item $json = $json->ascii ([$enable])
160 235
236=item $enabled = $json->get_ascii
237
161If C<$enable> is true (or missing), then the C<encode> method will not 238If C<$enable> is true (or missing), then the C<encode> method will not
162generate characters outside the code range C<0..127> (which is ASCII). Any 239generate characters outside the code range C<0..127> (which is ASCII). Any
163unicode characters outside that range will be escaped using either a 240Unicode characters outside that range will be escaped using either a
164single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, 241single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
165as per RFC4627. The resulting encoded JSON text can be treated as a native 242as per RFC4627. The resulting encoded JSON text can be treated as a native
166unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string, 243Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
167or any other superset of ASCII. 244or any other superset of ASCII.
168 245
169If C<$enable> is false, then the C<encode> method will not escape Unicode 246If C<$enable> is false, then the C<encode> method will not escape Unicode
170characters unless required by the JSON syntax or other flags. This results 247characters unless required by the JSON syntax or other flags. This results
171in a faster and more compact format. 248in a faster and more compact format.
172 249
250See also the section I<ENCODING/CODESET FLAG NOTES> later in this
251document.
252
173The main use for this flag is to produce JSON texts that can be 253The main use for this flag is to produce JSON texts that can be
174transmitted over a 7-bit channel, as the encoded JSON texts will not 254transmitted over a 7-bit channel, as the encoded JSON texts will not
175contain any 8 bit characters. 255contain any 8 bit characters.
176 256
177 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 257 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
178 => ["\ud801\udc01"] 258 => ["\ud801\udc01"]
179 259
180=item $json = $json->latin1 ([$enable]) 260=item $json = $json->latin1 ([$enable])
181 261
262=item $enabled = $json->get_latin1
263
182If C<$enable> is true (or missing), then the C<encode> method will encode 264If C<$enable> is true (or missing), then the C<encode> method will encode
183the resulting JSON text as latin1 (or iso-8859-1), escaping any characters 265the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
184outside the code range C<0..255>. The resulting string can be treated as a 266outside the code range C<0..255>. The resulting string can be treated as a
185latin1-encoded JSON text or a native unicode string. The C<decode> method 267latin1-encoded JSON text or a native Unicode string. The C<decode> method
186will not be affected in any way by this flag, as C<decode> by default 268will not be affected in any way by this flag, as C<decode> by default
187expects unicode, which is a strict superset of latin1. 269expects Unicode, which is a strict superset of latin1.
188 270
189If C<$enable> is false, then the C<encode> method will not escape Unicode 271If C<$enable> is false, then the C<encode> method will not escape Unicode
190characters unless required by the JSON syntax or other flags. 272characters unless required by the JSON syntax or other flags.
273
274See also the section I<ENCODING/CODESET FLAG NOTES> later in this
275document.
191 276
192The main use for this flag is efficiently encoding binary data as JSON 277The main use for this flag is efficiently encoding binary data as JSON
193text, as most octets will not be escaped, resulting in a smaller encoded 278text, as most octets will not be escaped, resulting in a smaller encoded
194size. The disadvantage is that the resulting JSON text is encoded 279size. The disadvantage is that the resulting JSON text is encoded
195in latin1 (and must correctly be treated as such when storing and 280in latin1 (and must correctly be treated as such when storing and
196transfering), a rare encoding for JSON. It is therefore most useful when 281transferring), a rare encoding for JSON. It is therefore most useful when
197you want to store data structures known to contain binary data efficiently 282you want to store data structures known to contain binary data efficiently
198in files or databases, not when talking to other JSON encoders/decoders. 283in files or databases, not when talking to other JSON encoders/decoders.
199 284
200 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] 285 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
201 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) 286 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
202 287
203=item $json = $json->utf8 ([$enable]) 288=item $json = $json->utf8 ([$enable])
289
290=item $enabled = $json->get_utf8
204 291
205If C<$enable> is true (or missing), then the C<encode> method will encode 292If C<$enable> is true (or missing), then the C<encode> method will encode
206the JSON result into UTF-8, as required by many protocols, while the 293the JSON result into UTF-8, as required by many protocols, while the
207C<decode> method expects to be handled an UTF-8-encoded string. Please 294C<decode> method expects to be handled an UTF-8-encoded string. Please
208note that UTF-8-encoded strings do not contain any characters outside the 295note that UTF-8-encoded strings do not contain any characters outside the
209range C<0..255>, they are thus useful for bytewise/binary I/O. In future 296range C<0..255>, they are thus useful for bytewise/binary I/O. In future
210versions, enabling this option might enable autodetection of the UTF-16 297versions, enabling this option might enable autodetection of the UTF-16
211and UTF-32 encoding families, as described in RFC4627. 298and UTF-32 encoding families, as described in RFC4627.
212 299
213If C<$enable> is false, then the C<encode> method will return the JSON 300If C<$enable> is false, then the C<encode> method will return the JSON
214string as a (non-encoded) unicode string, while C<decode> expects thus a 301string as a (non-encoded) Unicode string, while C<decode> expects thus a
215unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs 302Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
216to be done yourself, e.g. using the Encode module. 303to be done yourself, e.g. using the Encode module.
304
305See also the section I<ENCODING/CODESET FLAG NOTES> later in this
306document.
217 307
218Example, output UTF-16BE-encoded JSON: 308Example, output UTF-16BE-encoded JSON:
219 309
220 use Encode; 310 use Encode;
221 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); 311 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
242 ] 332 ]
243 } 333 }
244 334
245=item $json = $json->indent ([$enable]) 335=item $json = $json->indent ([$enable])
246 336
337=item $enabled = $json->get_indent
338
247If C<$enable> is true (or missing), then the C<encode> method will use a multiline 339If C<$enable> is true (or missing), then the C<encode> method will use a multiline
248format as output, putting every array member or object/hash key-value pair 340format as output, putting every array member or object/hash key-value pair
249into its own line, identing them properly. 341into its own line, indenting them properly.
250 342
251If C<$enable> is false, no newlines or indenting will be produced, and the 343If C<$enable> is false, no newlines or indenting will be produced, and the
252resulting JSON text is guarenteed not to contain any C<newlines>. 344resulting JSON text is guaranteed not to contain any C<newlines>.
253 345
254This setting has no effect when decoding JSON texts. 346This setting has no effect when decoding JSON texts.
255 347
256=item $json = $json->space_before ([$enable]) 348=item $json = $json->space_before ([$enable])
349
350=item $enabled = $json->get_space_before
257 351
258If C<$enable> is true (or missing), then the C<encode> method will add an extra 352If C<$enable> is true (or missing), then the C<encode> method will add an extra
259optional space before the C<:> separating keys from values in JSON objects. 353optional space before the C<:> separating keys from values in JSON objects.
260 354
261If C<$enable> is false, then the C<encode> method will not add any extra 355If C<$enable> is false, then the C<encode> method will not add any extra
267Example, space_before enabled, space_after and indent disabled: 361Example, space_before enabled, space_after and indent disabled:
268 362
269 {"key" :"value"} 363 {"key" :"value"}
270 364
271=item $json = $json->space_after ([$enable]) 365=item $json = $json->space_after ([$enable])
366
367=item $enabled = $json->get_space_after
272 368
273If C<$enable> is true (or missing), then the C<encode> method will add an extra 369If C<$enable> is true (or missing), then the C<encode> method will add an extra
274optional space after the C<:> separating keys from values in JSON objects 370optional space after the C<:> separating keys from values in JSON objects
275and extra whitespace after the C<,> separating key-value pairs and array 371and extra whitespace after the C<,> separating key-value pairs and array
276members. 372members.
282 378
283Example, space_before and indent disabled, space_after enabled: 379Example, space_before and indent disabled, space_after enabled:
284 380
285 {"key": "value"} 381 {"key": "value"}
286 382
383=item $json = $json->relaxed ([$enable])
384
385=item $enabled = $json->get_relaxed
386
387If C<$enable> is true (or missing), then C<decode> will accept some
388extensions to normal JSON syntax (see below). C<encode> will not be
389affected in anyway. I<Be aware that this option makes you accept invalid
390JSON texts as if they were valid!>. I suggest only to use this option to
391parse application-specific files written by humans (configuration files,
392resource files etc.)
393
394If C<$enable> is false (the default), then C<decode> will only accept
395valid JSON texts.
396
397Currently accepted extensions are:
398
399=over 4
400
401=item * list items can have an end-comma
402
403JSON I<separates> array elements and key-value pairs with commas. This
404can be annoying if you write JSON texts manually and want to be able to
405quickly append elements, so this extension accepts comma at the end of
406such items not just between them:
407
408 [
409 1,
410 2, <- this comma not normally allowed
411 ]
412 {
413 "k1": "v1",
414 "k2": "v2", <- this comma not normally allowed
415 }
416
417=item * shell-style '#'-comments
418
419Whenever JSON allows whitespace, shell-style comments are additionally
420allowed. They are terminated by the first carriage-return or line-feed
421character, after which more white-space and comments are allowed.
422
423 [
424 1, # this comment not allowed in JSON
425 # neither this one...
426 ]
427
428=back
429
287=item $json = $json->canonical ([$enable]) 430=item $json = $json->canonical ([$enable])
431
432=item $enabled = $json->get_canonical
288 433
289If C<$enable> is true (or missing), then the C<encode> method will output JSON objects 434If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
290by sorting their keys. This is adding a comparatively high overhead. 435by sorting their keys. This is adding a comparatively high overhead.
291 436
292If C<$enable> is false, then the C<encode> method will output key-value 437If C<$enable> is false, then the C<encode> method will output key-value
293pairs in the order Perl stores them (which will likely change between runs 438pairs in the order Perl stores them (which will likely change between runs
294of the same script). 439of the same script).
295 440
296This option is useful if you want the same data structure to be encoded as 441This option is useful if you want the same data structure to be encoded as
297the same JSON text (given the same overall settings). If it is disabled, 442the same JSON text (given the same overall settings). If it is disabled,
298the same hash migh be encoded differently even if contains the same data, 443the same hash might be encoded differently even if contains the same data,
299as key-value pairs have no inherent ordering in Perl. 444as key-value pairs have no inherent ordering in Perl.
300 445
301This setting has no effect when decoding JSON texts. 446This setting has no effect when decoding JSON texts.
302 447
303=item $json = $json->allow_nonref ([$enable]) 448=item $json = $json->allow_nonref ([$enable])
449
450=item $enabled = $json->get_allow_nonref
304 451
305If C<$enable> is true (or missing), then the C<encode> method can convert a 452If C<$enable> is true (or missing), then the C<encode> method can convert a
306non-reference into its corresponding string, number or null JSON value, 453non-reference into its corresponding string, number or null JSON value,
307which is an extension to RFC4627. Likewise, C<decode> will accept those JSON 454which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
308values instead of croaking. 455values instead of croaking.
316resulting in an invalid JSON text: 463resulting in an invalid JSON text:
317 464
318 JSON::XS->new->allow_nonref->encode ("Hello, World!") 465 JSON::XS->new->allow_nonref->encode ("Hello, World!")
319 => "Hello, World!" 466 => "Hello, World!"
320 467
468=item $json = $json->allow_unknown ([$enable])
469
470=item $enabled = $json->get_allow_unknown
471
472If C<$enable> is true (or missing), then C<encode> will I<not> throw an
473exception when it encounters values it cannot represent in JSON (for
474example, filehandles) but instead will encode a JSON C<null> value. Note
475that blessed objects are not included here and are handled separately by
476c<allow_nonref>.
477
478If C<$enable> is false (the default), then C<encode> will throw an
479exception when it encounters anything it cannot encode as JSON.
480
481This option does not affect C<decode> in any way, and it is recommended to
482leave it off unless you know your communications partner.
483
321=item $json = $json->allow_blessed ([$enable]) 484=item $json = $json->allow_blessed ([$enable])
485
486=item $enabled = $json->get_allow_blessed
322 487
323If C<$enable> is true (or missing), then the C<encode> method will not 488If C<$enable> is true (or missing), then the C<encode> method will not
324barf when it encounters a blessed reference. Instead, the value of the 489barf when it encounters a blessed reference. Instead, the value of the
325B<convert_blessed> option will decide wether C<null> (C<convert_blessed> 490B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
326disabled or no C<to_json> method found) or a representation of the 491disabled or no C<TO_JSON> method found) or a representation of the
327object (C<convert_blessed> enabled and C<to_json> method found) is being 492object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
328encoded. Has no effect on C<decode>. 493encoded. Has no effect on C<decode>.
329 494
330If C<$enable> is false (the default), then C<encode> will throw an 495If C<$enable> is false (the default), then C<encode> will throw an
331exception when it encounters a blessed object. 496exception when it encounters a blessed object.
332 497
333=item $json = $json->convert_blessed ([$enable]) 498=item $json = $json->convert_blessed ([$enable])
499
500=item $enabled = $json->get_convert_blessed
334 501
335If C<$enable> is true (or missing), then C<encode>, upon encountering a 502If C<$enable> is true (or missing), then C<encode>, upon encountering a
336blessed object, will check for the availability of the C<TO_JSON> method 503blessed object, will check for the availability of the C<TO_JSON> method
337on the object's class. If found, it will be called in scalar context 504on the object's class. If found, it will be called in scalar context
338and the resulting scalar will be encoded instead of the object. If no 505and the resulting scalar will be encoded instead of the object. If no
341 508
342The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON> 509The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
343returns other blessed objects, those will be handled in the same 510returns other blessed objects, those will be handled in the same
344way. C<TO_JSON> must take care of not causing an endless recursion cycle 511way. C<TO_JSON> must take care of not causing an endless recursion cycle
345(== crash) in this case. The name of C<TO_JSON> was chosen because other 512(== crash) in this case. The name of C<TO_JSON> was chosen because other
346methods called by the Perl core (== not the user of the object) are 513methods called by the Perl core (== not by the user of the object) are
347usually in upper case letters and to avoid collisions with the C<to_json> 514usually in upper case letters and to avoid collisions with any C<to_json>
348function. 515function or method.
349 516
350This setting does not yet influence C<decode> in any way, but in the 517This setting does not yet influence C<decode> in any way, but in the
351future, global hooks might get installed that influence C<decode> and are 518future, global hooks might get installed that influence C<decode> and are
352enabled by this setting. 519enabled by this setting.
353 520
354If C<$enable> is false, then the C<allow_blessed> setting will decide what 521If C<$enable> is false, then the C<allow_blessed> setting will decide what
355to do when a blessed object is found. 522to do when a blessed object is found.
356 523
524=item $json = $json->filter_json_object ([$coderef->($hashref)])
525
526When C<$coderef> is specified, it will be called from C<decode> each
527time it decodes a JSON object. The only argument is a reference to the
528newly-created hash. If the code references returns a single scalar (which
529need not be a reference), this value (i.e. a copy of that scalar to avoid
530aliasing) is inserted into the deserialised data structure. If it returns
531an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
532original deserialised hash will be inserted. This setting can slow down
533decoding considerably.
534
535When C<$coderef> is omitted or undefined, any existing callback will
536be removed and C<decode> will not change the deserialised hash in any
537way.
538
539Example, convert all JSON objects into the integer 5:
540
541 my $js = JSON::XS->new->filter_json_object (sub { 5 });
542 # returns [5]
543 $js->decode ('[{}]')
544 # throw an exception because allow_nonref is not enabled
545 # so a lone 5 is not allowed.
546 $js->decode ('{"a":1, "b":2}');
547
548=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
549
550Works remotely similar to C<filter_json_object>, but is only called for
551JSON objects having a single key named C<$key>.
552
553This C<$coderef> is called before the one specified via
554C<filter_json_object>, if any. It gets passed the single value in the JSON
555object. If it returns a single value, it will be inserted into the data
556structure. If it returns nothing (not even C<undef> but the empty list),
557the callback from C<filter_json_object> will be called next, as if no
558single-key callback were specified.
559
560If C<$coderef> is omitted or undefined, the corresponding callback will be
561disabled. There can only ever be one callback for a given key.
562
563As this callback gets called less often then the C<filter_json_object>
564one, decoding speed will not usually suffer as much. Therefore, single-key
565objects make excellent targets to serialise Perl objects into, especially
566as single-key JSON objects are as close to the type-tagged value concept
567as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
568support this in any way, so you need to make sure your data never looks
569like a serialised Perl hash.
570
571Typical names for the single object key are C<__class_whatever__>, or
572C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
573things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
574with real hashes.
575
576Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
577into the corresponding C<< $WIDGET{<id>} >> object:
578
579 # return whatever is in $WIDGET{5}:
580 JSON::XS
581 ->new
582 ->filter_json_single_key_object (__widget__ => sub {
583 $WIDGET{ $_[0] }
584 })
585 ->decode ('{"__widget__": 5')
586
587 # this can be used with a TO_JSON method in some "widget" class
588 # for serialisation to json:
589 sub WidgetBase::TO_JSON {
590 my ($self) = @_;
591
592 unless ($self->{id}) {
593 $self->{id} = ..get..some..id..;
594 $WIDGET{$self->{id}} = $self;
595 }
596
597 { __widget__ => $self->{id} }
598 }
599
357=item $json = $json->shrink ([$enable]) 600=item $json = $json->shrink ([$enable])
601
602=item $enabled = $json->get_shrink
358 603
359Perl usually over-allocates memory a bit when allocating space for 604Perl usually over-allocates memory a bit when allocating space for
360strings. This flag optionally resizes strings generated by either 605strings. This flag optionally resizes strings generated by either
361C<encode> or C<decode> to their minimum size possible. This can save 606C<encode> or C<decode> to their minimum size possible. This can save
362memory when your JSON texts are either very very long or you have many 607memory when your JSON texts are either very very long or you have many
380strings that look like integers or floats into integers or floats 625strings that look like integers or floats into integers or floats
381internally (there is no difference on the Perl level), saving space. 626internally (there is no difference on the Perl level), saving space.
382 627
383=item $json = $json->max_depth ([$maximum_nesting_depth]) 628=item $json = $json->max_depth ([$maximum_nesting_depth])
384 629
630=item $max_depth = $json->get_max_depth
631
385Sets the maximum nesting level (default C<512>) accepted while encoding 632Sets the maximum nesting level (default C<512>) accepted while encoding
386or decoding. If the JSON text or Perl data structure has an equal or 633or decoding. If a higher nesting level is detected in JSON text or a Perl
387higher nesting level then this limit, then the encoder and decoder will 634data structure, then the encoder and decoder will stop and croak at that
388stop and croak at that point. 635point.
389 636
390Nesting level is defined by number of hash- or arrayrefs that the encoder 637Nesting level is defined by number of hash- or arrayrefs that the encoder
391needs to traverse to reach a given point or the number of C<{> or C<[> 638needs to traverse to reach a given point or the number of C<{> or C<[>
392characters without their matching closing parenthesis crossed to reach a 639characters without their matching closing parenthesis crossed to reach a
393given character in a string. 640given character in a string.
394 641
395Setting the maximum depth to one disallows any nesting, so that ensures 642Setting the maximum depth to one disallows any nesting, so that ensures
396that the object is only a single hash/object or array. 643that the object is only a single hash/object or array.
397 644
398The argument to C<max_depth> will be rounded up to the next nearest power 645If no argument is given, the highest possible setting will be used, which
399of two. 646is rarely useful.
647
648Note that nesting is implemented by recursion in C. The default value has
649been chosen to be as large as typical operating systems allow without
650crashing.
651
652See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
653
654=item $json = $json->max_size ([$maximum_string_size])
655
656=item $max_size = $json->get_max_size
657
658Set the maximum length a JSON text may have (in bytes) where decoding is
659being attempted. The default is C<0>, meaning no limit. When C<decode>
660is called on a string that is longer then this many bytes, it will not
661attempt to decode the string but throw an exception. This setting has no
662effect on C<encode> (yet).
663
664If no argument is given, the limit check will be deactivated (same as when
665C<0> is specified).
400 666
401See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 667See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
402 668
403=item $json_text = $json->encode ($perl_scalar) 669=item $json_text = $json->encode ($perl_scalar)
404 670
433 => ([], 3) 699 => ([], 3)
434 700
435=back 701=back
436 702
437 703
704=head1 INCREMENTAL PARSING
705
706In some cases, there is the need for incremental parsing of JSON
707texts. While this module always has to keep both JSON text and resulting
708Perl data structure in memory at one time, it does allow you to parse a
709JSON stream incrementally. It does so by accumulating text until it has
710a full JSON object, which it then can decode. This process is similar to
711using C<decode_prefix> to see if a full JSON object is available, but
712is much more efficient (and can be implemented with a minimum of method
713calls).
714
715JSON::XS will only attempt to parse the JSON text once it is sure it
716has enough text to get a decisive result, using a very simple but
717truly incremental parser. This means that it sometimes won't stop as
718early as the full parser, for example, it doesn't detect parenthese
719mismatches. The only thing it guarantees is that it starts decoding as
720soon as a syntactically valid JSON text has been seen. This means you need
721to set resource limits (e.g. C<max_size>) to ensure the parser will stop
722parsing in the presence if syntax errors.
723
724The following methods implement this incremental parser.
725
726=over 4
727
728=item [void, scalar or list context] = $json->incr_parse ([$string])
729
730This is the central parsing function. It can both append new text and
731extract objects from the stream accumulated so far (both of these
732functions are optional).
733
734If C<$string> is given, then this string is appended to the already
735existing JSON fragment stored in the C<$json> object.
736
737After that, if the function is called in void context, it will simply
738return without doing anything further. This can be used to add more text
739in as many chunks as you want.
740
741If the method is called in scalar context, then it will try to extract
742exactly I<one> JSON object. If that is successful, it will return this
743object, otherwise it will return C<undef>. If there is a parse error,
744this method will croak just as C<decode> would do (one can then use
745C<incr_skip> to skip the errornous part). This is the most common way of
746using the method.
747
748And finally, in list context, it will try to extract as many objects
749from the stream as it can find and return them, or the empty list
750otherwise. For this to work, there must be no separators between the JSON
751objects or arrays, instead they must be concatenated back-to-back. If
752an error occurs, an exception will be raised as in the scalar context
753case. Note that in this case, any previously-parsed JSON texts will be
754lost.
755
756=item $lvalue_string = $json->incr_text
757
758This method returns the currently stored JSON fragment as an lvalue, that
759is, you can manipulate it. This I<only> works when a preceding call to
760C<incr_parse> in I<scalar context> successfully returned an object. Under
761all other circumstances you must not call this function (I mean it.
762although in simple tests it might actually work, it I<will> fail under
763real world conditions). As a special exception, you can also call this
764method before having parsed anything.
765
766This function is useful in two cases: a) finding the trailing text after a
767JSON object or b) parsing multiple JSON objects separated by non-JSON text
768(such as commas).
769
770=item $json->incr_skip
771
772This will reset the state of the incremental parser and will remove the
773parsed text from the input buffer. This is useful after C<incr_parse>
774died, in which case the input buffer and incremental parser state is left
775unchanged, to skip the text parsed so far and to reset the parse state.
776
777=item $json->incr_reset
778
779This completely resets the incremental parser, that is, after this call,
780it will be as if the parser had never parsed anything.
781
782This is useful if you want ot repeatedly parse JSON objects and want to
783ignore any trailing data, which means you have to reset the parser after
784each successful decode.
785
786=back
787
788=head2 LIMITATIONS
789
790All options that affect decoding are supported, except
791C<allow_nonref>. The reason for this is that it cannot be made to
792work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
793them back to back and still decode them perfectly. This does not hold true
794for JSON numbers, however.
795
796For example, is the string C<1> a single JSON number, or is it simply the
797start of C<12>? Or is C<12> a single JSON number, or the concatenation
798of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
799takes the conservative route and disallows this case.
800
801=head2 EXAMPLES
802
803Some examples will make all this clearer. First, a simple example that
804works similarly to C<decode_prefix>: We want to decode the JSON object at
805the start of a string and identify the portion after the JSON object:
806
807 my $text = "[1,2,3] hello";
808
809 my $json = new JSON::XS;
810
811 my $obj = $json->incr_parse ($text)
812 or die "expected JSON object or array at beginning of string";
813
814 my $tail = $json->incr_text;
815 # $tail now contains " hello"
816
817Easy, isn't it?
818
819Now for a more complicated example: Imagine a hypothetical protocol where
820you read some requests from a TCP stream, and each request is a JSON
821array, without any separation between them (in fact, it is often useful to
822use newlines as "separators", as these get interpreted as whitespace at
823the start of the JSON text, which makes it possible to test said protocol
824with C<telnet>...).
825
826Here is how you'd do it (it is trivial to write this in an event-based
827manner):
828
829 my $json = new JSON::XS;
830
831 # read some data from the socket
832 while (sysread $socket, my $buf, 4096) {
833
834 # split and decode as many requests as possible
835 for my $request ($json->incr_parse ($buf)) {
836 # act on the $request
837 }
838 }
839
840Another complicated example: Assume you have a string with JSON objects
841or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
842[3]>). To parse them, we have to skip the commas between the JSON texts,
843and here is where the lvalue-ness of C<incr_text> comes in useful:
844
845 my $text = "[1],[2], [3]";
846 my $json = new JSON::XS;
847
848 # void context, so no parsing done
849 $json->incr_parse ($text);
850
851 # now extract as many objects as possible. note the
852 # use of scalar context so incr_text can be called.
853 while (my $obj = $json->incr_parse) {
854 # do something with $obj
855
856 # now skip the optional comma
857 $json->incr_text =~ s/^ \s* , //x;
858 }
859
860Now lets go for a very complex example: Assume that you have a gigantic
861JSON array-of-objects, many gigabytes in size, and you want to parse it,
862but you cannot load it into memory fully (this has actually happened in
863the real world :).
864
865Well, you lost, you have to implement your own JSON parser. But JSON::XS
866can still help you: You implement a (very simple) array parser and let
867JSON decode the array elements, which are all full JSON objects on their
868own (this wouldn't work if the array elements could be JSON numbers, for
869example):
870
871 my $json = new JSON::XS;
872
873 # open the monster
874 open my $fh, "<bigfile.json"
875 or die "bigfile: $!";
876
877 # first parse the initial "["
878 for (;;) {
879 sysread $fh, my $buf, 65536
880 or die "read error: $!";
881 $json->incr_parse ($buf); # void context, so no parsing
882
883 # Exit the loop once we found and removed(!) the initial "[".
884 # In essence, we are (ab-)using the $json object as a simple scalar
885 # we append data to.
886 last if $json->incr_text =~ s/^ \s* \[ //x;
887 }
888
889 # now we have the skipped the initial "[", so continue
890 # parsing all the elements.
891 for (;;) {
892 # in this loop we read data until we got a single JSON object
893 for (;;) {
894 if (my $obj = $json->incr_parse) {
895 # do something with $obj
896 last;
897 }
898
899 # add more data
900 sysread $fh, my $buf, 65536
901 or die "read error: $!";
902 $json->incr_parse ($buf); # void context, so no parsing
903 }
904
905 # in this loop we read data until we either found and parsed the
906 # separating "," between elements, or the final "]"
907 for (;;) {
908 # first skip whitespace
909 $json->incr_text =~ s/^\s*//;
910
911 # if we find "]", we are done
912 if ($json->incr_text =~ s/^\]//) {
913 print "finished.\n";
914 exit;
915 }
916
917 # if we find ",", we can continue with the next element
918 if ($json->incr_text =~ s/^,//) {
919 last;
920 }
921
922 # if we find anything else, we have a parse error!
923 if (length $json->incr_text) {
924 die "parse error near ", $json->incr_text;
925 }
926
927 # else add more data
928 sysread $fh, my $buf, 65536
929 or die "read error: $!";
930 $json->incr_parse ($buf); # void context, so no parsing
931 }
932
933This is a complex example, but most of the complexity comes from the fact
934that we are trying to be correct (bear with me if I am wrong, I never ran
935the above example :).
936
937
938
438=head1 MAPPING 939=head1 MAPPING
439 940
440This section describes how JSON::XS maps Perl values to JSON values and 941This section describes how JSON::XS maps Perl values to JSON values and
441vice versa. These mappings are designed to "do the right thing" in most 942vice versa. These mappings are designed to "do the right thing" in most
442circumstances automatically, preserving round-tripping characteristics 943circumstances automatically, preserving round-tripping characteristics
443(what you put in comes out as something equivalent). 944(what you put in comes out as something equivalent).
444 945
445For the more enlightened: note that in the following descriptions, 946For the more enlightened: note that in the following descriptions,
446lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl> 947lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
447refers to the abstract Perl language itself. 948refers to the abstract Perl language itself.
448 949
449 950
450=head2 JSON -> PERL 951=head2 JSON -> PERL
451 952
452=over 4 953=over 4
453 954
454=item object 955=item object
455 956
456A JSON object becomes a reference to a hash in Perl. No ordering of object 957A JSON object becomes a reference to a hash in Perl. No ordering of object
457keys is preserved (JSON does not preserver object key ordering itself). 958keys is preserved (JSON does not preserve object key ordering itself).
458 959
459=item array 960=item array
460 961
461A JSON array becomes a reference to an array in Perl. 962A JSON array becomes a reference to an array in Perl.
462 963
466are represented by the same codepoints in the Perl string, so no manual 967are represented by the same codepoints in the Perl string, so no manual
467decoding is necessary. 968decoding is necessary.
468 969
469=item number 970=item number
470 971
471A JSON number becomes either an integer or numeric (floating point) 972A JSON number becomes either an integer, numeric (floating point) or
472scalar in perl, depending on its range and any fractional parts. On the 973string scalar in perl, depending on its range and any fractional parts. On
473Perl level, there is no difference between those as Perl handles all the 974the Perl level, there is no difference between those as Perl handles all
474conversion details, but an integer may take slightly less memory and might 975the conversion details, but an integer may take slightly less memory and
475represent more values exactly than (floating point) numbers. 976might represent more values exactly than floating point numbers.
977
978If the number consists of digits only, JSON::XS will try to represent
979it as an integer value. If that fails, it will try to represent it as
980a numeric (floating point) value if that is possible without loss of
981precision. Otherwise it will preserve the number as a string value (in
982which case you lose roundtripping ability, as the JSON number will be
983re-encoded toa JSON string).
984
985Numbers containing a fractional or exponential part will always be
986represented as numeric (floating point) values, possibly at a loss of
987precision (in which case you might lose perfect roundtripping ability, but
988the JSON number will still be re-encoded as a JSON number).
476 989
477=item true, false 990=item true, false
478 991
479These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, 992These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
480respectively. They are overloaded to act almost exactly like the numbers 993respectively. They are overloaded to act almost exactly like the numbers
481C<1> and C<0>. You can check wether a scalar is a JSON boolean by using 994C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
482the C<JSON::XS::is_bool> function. 995the C<JSON::XS::is_bool> function.
483 996
484=item null 997=item null
485 998
486A JSON null atom becomes C<undef> in Perl. 999A JSON null atom becomes C<undef> in Perl.
517Other unblessed references are generally not allowed and will cause an 1030Other unblessed references are generally not allowed and will cause an
518exception to be thrown, except for references to the integers C<0> and 1031exception to be thrown, except for references to the integers C<0> and
519C<1>, which get turned into C<false> and C<true> atoms in JSON. You can 1032C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
520also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. 1033also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
521 1034
522 to_json [\0,JSON::XS::true] # yields [false,true] 1035 encode_json [\0, JSON::XS::true] # yields [false,true]
523 1036
524=item JSON::XS::true, JSON::XS::false 1037=item JSON::XS::true, JSON::XS::false
525 1038
526These special values become JSON true and JSON false values, 1039These special values become JSON true and JSON false values,
527respectively. You cna alos use C<\1> and C<\0> directly if you want. 1040respectively. You can also use C<\1> and C<\0> directly if you want.
528 1041
529=item blessed objects 1042=item blessed objects
530 1043
531Blessed objects are not allowed. JSON::XS currently tries to encode their 1044Blessed objects are not directly representable in JSON. See the
532underlying representation (hash- or arrayref), but this behaviour might 1045C<allow_blessed> and C<convert_blessed> methods on various options on
533change in future versions. 1046how to deal with this: basically, you can choose between throwing an
1047exception, encoding the reference as if it weren't blessed, or provide
1048your own serialiser method.
534 1049
535=item simple scalars 1050=item simple scalars
536 1051
537Simple Perl scalars (any scalar that is not a reference) are the most 1052Simple Perl scalars (any scalar that is not a reference) are the most
538difficult objects to encode: JSON::XS will encode undefined scalars as 1053difficult objects to encode: JSON::XS will encode undefined scalars as
539JSON null value, scalars that have last been used in a string context 1054JSON C<null> values, scalars that have last been used in a string context
540before encoding as JSON strings and anything else as number value: 1055before encoding as JSON strings, and anything else as number value:
541 1056
542 # dump as number 1057 # dump as number
543 to_json [2] # yields [2] 1058 encode_json [2] # yields [2]
544 to_json [-3.0e17] # yields [-3e+17] 1059 encode_json [-3.0e17] # yields [-3e+17]
545 my $value = 5; to_json [$value] # yields [5] 1060 my $value = 5; encode_json [$value] # yields [5]
546 1061
547 # used as string, so dump as string 1062 # used as string, so dump as string
548 print $value; 1063 print $value;
549 to_json [$value] # yields ["5"] 1064 encode_json [$value] # yields ["5"]
550 1065
551 # undef becomes null 1066 # undef becomes null
552 to_json [undef] # yields [null] 1067 encode_json [undef] # yields [null]
553 1068
554You can force the type to be a string by stringifying it: 1069You can force the type to be a JSON string by stringifying it:
555 1070
556 my $x = 3.1; # some variable containing a number 1071 my $x = 3.1; # some variable containing a number
557 "$x"; # stringified 1072 "$x"; # stringified
558 $x .= ""; # another, more awkward way to stringify 1073 $x .= ""; # another, more awkward way to stringify
559 print $x; # perl does it for you, too, quite often 1074 print $x; # perl does it for you, too, quite often
560 1075
561You can force the type to be a number by numifying it: 1076You can force the type to be a JSON number by numifying it:
562 1077
563 my $x = "3"; # some variable containing a string 1078 my $x = "3"; # some variable containing a string
564 $x += 0; # numify it, ensuring it will be dumped as a number 1079 $x += 0; # numify it, ensuring it will be dumped as a number
565 $x *= 1; # same thing, the choise is yours. 1080 $x *= 1; # same thing, the choice is yours.
566 1081
567You can not currently output JSON booleans or force the type in other, 1082You can not currently force the type in other, less obscure, ways. Tell me
568less obscure, ways. Tell me if you need this capability. 1083if you need this capability (but don't forget to explain why it's needed
1084:).
569 1085
570=back 1086=back
571 1087
572 1088
573=head1 COMPARISON 1089=head1 ENCODING/CODESET FLAG NOTES
574 1090
575As already mentioned, this module was created because none of the existing 1091The interested reader might have seen a number of flags that signify
576JSON modules could be made to work correctly. First I will describe the 1092encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
577problems (or pleasures) I encountered with various existing JSON modules, 1093some confusion on what these do, so here is a short comparison:
578followed by some benchmark values. JSON::XS was designed not to suffer 1094
579from any of these problems or limitations. 1095C<utf8> controls whether the JSON text created by C<encode> (and expected
1096by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
1097control whether C<encode> escapes character values outside their respective
1098codeset range. Neither of these flags conflict with each other, although
1099some combinations make less sense than others.
1100
1101Care has been taken to make all flags symmetrical with respect to
1102C<encode> and C<decode>, that is, texts encoded with any combination of
1103these flag values will be correctly decoded when the same flags are used
1104- in general, if you use different flag settings while encoding vs. when
1105decoding you likely have a bug somewhere.
1106
1107Below comes a verbose discussion of these flags. Note that a "codeset" is
1108simply an abstract set of character-codepoint pairs, while an encoding
1109takes those codepoint numbers and I<encodes> them, in our case into
1110octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
1111and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
1112the same time, which can be confusing.
580 1113
581=over 4 1114=over 4
582 1115
583=item JSON 1.07 1116=item C<utf8> flag disabled
584 1117
585Slow (but very portable, as it is written in pure Perl). 1118When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
1119and expect Unicode strings, that is, characters with high ordinal Unicode
1120values (> 255) will be encoded as such characters, and likewise such
1121characters are decoded as-is, no canges to them will be done, except
1122"(re-)interpreting" them as Unicode codepoints or Unicode characters,
1123respectively (to Perl, these are the same thing in strings unless you do
1124funny/weird/dumb stuff).
586 1125
587Undocumented/buggy Unicode handling (how JSON handles unicode values is 1126This is useful when you want to do the encoding yourself (e.g. when you
588undocumented. One can get far by feeding it unicode strings and doing 1127want to have UTF-16 encoded JSON texts) or when some other layer does
589en-/decoding oneself, but unicode escapes are not working properly). 1128the encoding for you (for example, when printing to a terminal using a
1129filehandle that transparently encodes to UTF-8 you certainly do NOT want
1130to UTF-8 encode your data first and have Perl encode it another time).
590 1131
591No roundtripping (strings get clobbered if they look like numbers, e.g. 1132=item C<utf8> flag enabled
592the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
593decode into the number 2.
594 1133
595=item JSON::PC 0.01 1134If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
1135characters using the corresponding UTF-8 multi-byte sequence, and will
1136expect your input strings to be encoded as UTF-8, that is, no "character"
1137of the input string must have any value > 255, as UTF-8 does not allow
1138that.
596 1139
597Very fast. 1140The C<utf8> flag therefore switches between two modes: disabled means you
1141will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
1142octet/binary string in Perl.
598 1143
599Undocumented/buggy Unicode handling. 1144=item C<latin1> or C<ascii> flags enabled
600 1145
601No roundtripping. 1146With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
1147with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
1148characters as specified by the C<utf8> flag.
602 1149
603Has problems handling many Perl values (e.g. regex results and other magic 1150If C<utf8> is disabled, then the result is also correctly encoded in those
604values will make it croak). 1151character sets (as both are proper subsets of Unicode, meaning that a
1152Unicode string with all character values < 256 is the same thing as a
1153ISO-8859-1 string, and a Unicode string with all character values < 128 is
1154the same thing as an ASCII string in Perl).
605 1155
606Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> 1156If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
607which is not a valid JSON text. 1157regardless of these flags, just some more characters will be escaped using
1158C<\uXXXX> then before.
608 1159
609Unmaintained (maintainer unresponsive for many months, bugs are not 1160Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
610getting fixed). 1161encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
1162encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
1163a subset of Unicode), while ASCII is.
611 1164
612=item JSON::Syck 0.21 1165Surprisingly, C<decode> will ignore these flags and so treat all input
1166values as governed by the C<utf8> flag. If it is disabled, this allows you
1167to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
1168Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
613 1169
614Very buggy (often crashes). 1170So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
1171they only govern when the JSON output engine escapes a character or not.
615 1172
616Very inflexible (no human-readable format supported, format pretty much 1173The main use for C<latin1> is to relatively efficiently store binary data
617undocumented. I need at least a format for easy reading by humans and a 1174as JSON, at the expense of breaking compatibility with most JSON decoders.
618single-line compact format for use in a protocol, and preferably a way to
619generate ASCII-only JSON texts).
620 1175
621Completely broken (and confusingly documented) Unicode handling (unicode 1176The main use for C<ascii> is to force the output to not contain characters
622escapes are not working properly, you need to set ImplicitUnicode to 1177with values > 127, which means you can interpret the resulting string
623I<different> values on en- and decoding to get symmetric behaviour). 1178as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
624 11798-bit-encoding, and still get the same data structure back. This is useful
625No roundtripping (simple cases work, but this depends on wether the scalar 1180when your channel for JSON transfer is not 8-bit clean or the encoding
626value was used in a numeric context or not). 1181might be mangled in between (e.g. in mail), and works because ASCII is a
627 1182proper subset of most 8-bit and multibyte encodings in use in the world.
628Dumping hashes may skip hash values depending on iterator state.
629
630Unmaintained (maintainer unresponsive for many months, bugs are not
631getting fixed).
632
633Does not check input for validity (i.e. will accept non-JSON input and
634return "something" instead of raising an exception. This is a security
635issue: imagine two banks transfering money between each other using
636JSON. One bank might parse a given non-JSON request and deduct money,
637while the other might reject the transaction with a syntax error. While a
638good protocol will at least recover, that is extra unnecessary work and
639the transaction will still not succeed).
640
641=item JSON::DWIW 0.04
642
643Very fast. Very natural. Very nice.
644
645Undocumented unicode handling (but the best of the pack. Unicode escapes
646still don't get parsed properly).
647
648Very inflexible.
649
650No roundtripping.
651
652Does not generate valid JSON texts (key strings are often unquoted, empty keys
653result in nothing being output)
654
655Does not check input for validity.
656 1183
657=back 1184=back
658 1185
659 1186
660=head2 JSON and YAML 1187=head2 JSON and YAML
661 1188
662You often hear that JSON is a subset (or a close subset) of YAML. This is, 1189You often hear that JSON is a subset of YAML. This is, however, a mass
663however, a mass hysteria and very far from the truth. In general, there is 1190hysteria(*) and very far from the truth (as of the time of this writing),
664no way to configure JSON::XS to output a data structure as valid YAML. 1191so let me state it clearly: I<in general, there is no way to configure
1192JSON::XS to output a data structure as valid YAML> that works in all
1193cases.
665 1194
666If you really must use JSON::XS to generate YAML, you should use this 1195If you really must use JSON::XS to generate YAML, you should use this
667algorithm (subject to change in future versions): 1196algorithm (subject to change in future versions):
668 1197
669 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1198 my $to_yaml = JSON::XS->new->utf8->space_after (1);
670 my $yaml = $to_yaml->encode ($ref) . "\n"; 1199 my $yaml = $to_yaml->encode ($ref) . "\n";
671 1200
672This will usually generate JSON texts that also parse as valid 1201This will I<usually> generate JSON texts that also parse as valid
673YAML. Please note that YAML has hardcoded limits on (simple) object key 1202YAML. Please note that YAML has hardcoded limits on (simple) object key
674lengths that JSON doesn't have, so you should make sure that your hash 1203lengths that JSON doesn't have and also has different and incompatible
1204unicode handling, so you should make sure that your hash keys are
675keys are noticably shorter than the 1024 characters YAML allows. 1205noticeably shorter than the 1024 "stream characters" YAML allows and that
1206you do not have characters with codepoint values outside the Unicode BMP
1207(basic multilingual page). YAML also does not allow C<\/> sequences in
1208strings (which JSON::XS does not I<currently> generate, but other JSON
1209generators might).
676 1210
677There might be other incompatibilities that I am not aware of. In general 1211There might be other incompatibilities that I am not aware of (or the YAML
1212specification has been changed yet again - it does so quite often). In
678you should not try to generate YAML with a JSON generator or vice versa, 1213general you should not try to generate YAML with a JSON generator or vice
679or try to parse JSON with a YAML parser or vice versa: chances are high 1214versa, or try to parse JSON with a YAML parser or vice versa: chances are
680that you will run into severe interoperability problems. 1215high that you will run into severe interoperability problems when you
1216least expect it.
1217
1218=over 4
1219
1220=item (*)
1221
1222I have been pressured multiple times by Brian Ingerson (one of the
1223authors of the YAML specification) to remove this paragraph, despite him
1224acknowledging that the actual incompatibilities exist. As I was personally
1225bitten by this "JSON is YAML" lie, I refused and said I will continue to
1226educate people about these issues, so others do not run into the same
1227problem again and again. After this, Brian called me a (quote)I<complete
1228and worthless idiot>(unquote).
1229
1230In my opinion, instead of pressuring and insulting people who actually
1231clarify issues with YAML and the wrong statements of some of its
1232proponents, I would kindly suggest reading the JSON spec (which is not
1233that difficult or long) and finally make YAML compatible to it, and
1234educating users about the changes, instead of spreading lies about the
1235real compatibility for many I<years> and trying to silence people who
1236point out that it isn't true.
1237
1238=back
681 1239
682 1240
683=head2 SPEED 1241=head2 SPEED
684 1242
685It seems that JSON::XS is surprisingly fast, as shown in the following 1243It seems that JSON::XS is surprisingly fast, as shown in the following
686tables. They have been generated with the help of the C<eg/bench> program 1244tables. They have been generated with the help of the C<eg/bench> program
687in the JSON::XS distribution, to make it easy to compare on your own 1245in the JSON::XS distribution, to make it easy to compare on your own
688system. 1246system.
689 1247
690First comes a comparison between various modules using a very short 1248First comes a comparison between various modules using
691single-line JSON string: 1249a very short single-line JSON string (also available at
1250L<http://dist.schmorp.de/misc/json/short.json>).
692 1251
693 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1252 {"method": "handleMessage", "params": ["user1",
694 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1253 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1254 true, false]}
695 1255
696It shows the number of encodes/decodes per second (JSON::XS uses 1256It shows the number of encodes/decodes per second (JSON::XS uses
697the functional interface, while JSON::XS/2 uses the OO interface 1257the functional interface, while JSON::XS/2 uses the OO interface
698with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables 1258with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
699shrink). Higher is better: 1259shrink). Higher is better:
700 1260
701 module | encode | decode | 1261 module | encode | decode |
702 -----------|------------|------------| 1262 -----------|------------|------------|
703 JSON | 7645.468 | 4208.613 | 1263 JSON 1.x | 4990.842 | 4088.813 |
704 JSON::DWIW | 40721.398 | 77101.176 | 1264 JSON::DWIW | 51653.990 | 71575.154 |
705 JSON::PC | 65948.176 | 78251.940 | 1265 JSON::PC | 65948.176 | 74631.744 |
706 JSON::Syck | 22844.793 | 26479.192 | 1266 JSON::PP | 8931.652 | 3817.168 |
1267 JSON::Syck | 24877.248 | 27776.848 |
707 JSON::XS | 388361.481 | 199728.762 | 1268 JSON::XS | 388361.481 | 227951.304 |
708 JSON::XS/2 | 218453.333 | 192399.266 | 1269 JSON::XS/2 | 227951.304 | 218453.333 |
709 JSON::XS/3 | 338250.323 | 192399.266 | 1270 JSON::XS/3 | 338250.323 | 218453.333 |
710 Storable | 15779.925 | 14169.946 | 1271 Storable | 16500.016 | 135300.129 |
711 -----------+------------+------------+ 1272 -----------+------------+------------+
712 1273
713That is, JSON::XS is about five times faster than JSON::DWIW on encoding, 1274That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
714about three times faster on decoding, and over fourty times faster 1275about three times faster on decoding, and over forty times faster
715than JSON, even with pretty-printing and key sorting. It also compares 1276than JSON, even with pretty-printing and key sorting. It also compares
716favourably to Storable for small amounts of data. 1277favourably to Storable for small amounts of data.
717 1278
718Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1279Using a longer test string (roughly 18KB, generated from Yahoo! Locals
719search API (http://nanoref.com/yahooapis/mgPdGg): 1280search API (L<http://dist.schmorp.de/misc/json/long.json>).
720 1281
721 module | encode | decode | 1282 module | encode | decode |
722 -----------|------------|------------| 1283 -----------|------------|------------|
723 JSON | 254.685 | 37.665 | 1284 JSON 1.x | 55.260 | 34.971 |
724 JSON::DWIW | 843.343 | 1049.731 | 1285 JSON::DWIW | 825.228 | 1082.513 |
725 JSON::PC | 3602.116 | 2307.352 | 1286 JSON::PC | 3571.444 | 2394.829 |
1287 JSON::PP | 210.987 | 32.574 |
726 JSON::Syck | 505.107 | 787.899 | 1288 JSON::Syck | 552.551 | 787.544 |
727 JSON::XS | 5747.196 | 3690.220 | 1289 JSON::XS | 5780.463 | 4854.519 |
728 JSON::XS/2 | 3968.121 | 3676.634 | 1290 JSON::XS/2 | 3869.998 | 4798.975 |
729 JSON::XS/3 | 6105.246 | 3662.508 | 1291 JSON::XS/3 | 5862.880 | 4798.975 |
730 Storable | 4417.337 | 5285.161 | 1292 Storable | 4445.002 | 5235.027 |
731 -----------+------------+------------+ 1293 -----------+------------+------------+
732 1294
733Again, JSON::XS leads by far (except for Storable which non-surprisingly 1295Again, JSON::XS leads by far (except for Storable which non-surprisingly
734decodes faster). 1296decodes faster).
735 1297
736On large strings containing lots of high unicode characters, some modules 1298On large strings containing lots of high Unicode characters, some modules
737(such as JSON::PC) seem to decode faster than JSON::XS, but the result 1299(such as JSON::PC) seem to decode faster than JSON::XS, but the result
738will be broken due to missing (or wrong) unicode handling. Others refuse 1300will be broken due to missing (or wrong) Unicode handling. Others refuse
739to decode or encode properly, so it was impossible to prepare a fair 1301to decode or encode properly, so it was impossible to prepare a fair
740comparison table for that case. 1302comparison table for that case.
741 1303
742 1304
743=head1 SECURITY CONSIDERATIONS 1305=head1 SECURITY CONSIDERATIONS
749any buffer overflows. Obviously, this module should ensure that and I am 1311any buffer overflows. Obviously, this module should ensure that and I am
750trying hard on making that true, but you never know. 1312trying hard on making that true, but you never know.
751 1313
752Second, you need to avoid resource-starving attacks. That means you should 1314Second, you need to avoid resource-starving attacks. That means you should
753limit the size of JSON texts you accept, or make sure then when your 1315limit the size of JSON texts you accept, or make sure then when your
754resources run out, thats just fine (e.g. by using a separate process that 1316resources run out, that's just fine (e.g. by using a separate process that
755can crash safely). The size of a JSON text in octets or characters is 1317can crash safely). The size of a JSON text in octets or characters is
756usually a good indication of the size of the resources required to decode 1318usually a good indication of the size of the resources required to decode
757it into a Perl structure. 1319it into a Perl structure. While JSON::XS can check the size of the JSON
1320text, it might be too late when you already have it in memory, so you
1321might want to check the size before you accept the string.
758 1322
759Third, JSON::XS recurses using the C stack when decoding objects and 1323Third, JSON::XS recurses using the C stack when decoding objects and
760arrays. The C stack is a limited resource: for instance, on my amd64 1324arrays. The C stack is a limited resource: for instance, on my amd64
761machine with 8MB of stack size I can decode around 180k nested arrays but 1325machine with 8MB of stack size I can decode around 180k nested arrays but
762only 14k nested JSON objects (due to perl itself recursing deeply on croak 1326only 14k nested JSON objects (due to perl itself recursing deeply on croak
763to free the temporary). If that is exceeded, the program crashes. to be 1327to free the temporary). If that is exceeded, the program crashes. To be
764conservative, the default nesting limit is set to 512. If your process 1328conservative, the default nesting limit is set to 512. If your process
765has a smaller stack, you should adjust this setting accordingly with the 1329has a smaller stack, you should adjust this setting accordingly with the
766C<max_depth> method. 1330C<max_depth> method.
767 1331
768And last but least, something else could bomb you that I forgot to think 1332Something else could bomb you, too, that I forgot to think of. In that
769of. In that case, you get to keep the pieces. I am always open for hints, 1333case, you get to keep the pieces. I am always open for hints, though...
770though... 1334
1335Also keep in mind that JSON::XS might leak contents of your Perl data
1336structures in its error messages, so when you serialise sensitive
1337information you might want to make sure that exceptions thrown by JSON::XS
1338will not end up in front of untrusted eyes.
771 1339
772If you are using JSON::XS to return packets to consumption 1340If you are using JSON::XS to return packets to consumption
773by javascript scripts in a browser you should have a look at 1341by JavaScript scripts in a browser you should have a look at
774L<http://jpsykes.com/47/practical-csrf-and-json-security> to see wether 1342L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
775you are vulnerable to some common attack vectors (which really are browser 1343you are vulnerable to some common attack vectors (which really are browser
776design bugs, but it is still you who will have to deal with it, as major 1344design bugs, but it is still you who will have to deal with it, as major
777browser developers care only for features, not about doing security 1345browser developers care only for features, not about getting security
778right). 1346right).
779 1347
780 1348
1349=head1 THREADS
1350
1351This module is I<not> guaranteed to be thread safe and there are no
1352plans to change this until Perl gets thread support (as opposed to the
1353horribly slow so-called "threads" which are simply slow and bloated
1354process simulations - use fork, it's I<much> faster, cheaper, better).
1355
1356(It might actually work, but you have been warned).
1357
1358
781=head1 BUGS 1359=head1 BUGS
782 1360
783While the goal of this module is to be correct, that unfortunately does 1361While the goal of this module is to be correct, that unfortunately does
784not mean its bug-free, only that I think its design is bug-free. It is 1362not mean it's bug-free, only that I think its design is bug-free. If you
785still relatively early in its development. If you keep reporting bugs they 1363keep reporting bugs they will be fixed swiftly, though.
786will be fixed swiftly, though. 1364
1365Please refrain from using rt.cpan.org or any other bug reporting
1366service. I put the contact address into my modules for a reason.
787 1367
788=cut 1368=cut
789 1369
790our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" }; 1370our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
791our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" }; 1371our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
808 "--" => sub { $_[0] = ${$_[0]} - 1 }, 1388 "--" => sub { $_[0] = ${$_[0]} - 1 },
809 fallback => 1; 1389 fallback => 1;
810 1390
8111; 13911;
812 1392
1393=head1 SEE ALSO
1394
1395The F<json_xs> command line utility for quick experiments.
1396
813=head1 AUTHOR 1397=head1 AUTHOR
814 1398
815 Marc Lehmann <schmorp@schmorp.de> 1399 Marc Lehmann <schmorp@schmorp.de>
816 http://home.schmorp.de/ 1400 http://home.schmorp.de/
817 1401

Diff Legend

Removed lines
+ Added lines
< Changed lines
> Changed lines