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Revision 1.47 by root, Mon Jun 25 06:57:42 2007 UTC vs.
Revision 1.94 by root, Tue Mar 25 07:46:15 2008 UTC

1=head1 NAME 1=head1 NAME
2 2
3=encoding utf-8
4
3JSON::XS - JSON serialising/deserialising, done correctly and fast 5JSON::XS - JSON serialising/deserialising, done correctly and fast
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
42overriden) with no overhead due to emulation (by inheritign 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 datatypes 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 objetc
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 $VERSION = '2.1';
91our @ISA = qw(Exporter); 109our @ISA = qw(Exporter);
92 110
93our @EXPORT = qw(to_json from_json objToJson jsonToObj); 111our @EXPORT = qw(encode_json decode_json to_json from_json);
112
113sub to_json($) {
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
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 codepoint.
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.
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
321=item $json = $json->allow_blessed ([$enable]) 468=item $json = $json->allow_blessed ([$enable])
322 469
470=item $enabled = $json->get_allow_blessed
471
323If C<$enable> is true (or missing), then the C<encode> method will not 472If C<$enable> is true (or missing), then the C<encode> method will not
324barf when it encounters a blessed reference. Instead, the value of the 473barf when it encounters a blessed reference. Instead, the value of the
325B<convert_blessed> option will decide wether C<null> (C<convert_blessed> 474B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
326disabled or no C<to_json> method found) or a representation of the 475disabled or no C<TO_JSON> method found) or a representation of the
327object (C<convert_blessed> enabled and C<to_json> method found) is being 476object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
328encoded. Has no effect on C<decode>. 477encoded. Has no effect on C<decode>.
329 478
330If C<$enable> is false (the default), then C<encode> will throw an 479If C<$enable> is false (the default), then C<encode> will throw an
331exception when it encounters a blessed object. 480exception when it encounters a blessed object.
332 481
333=item $json = $json->convert_blessed ([$enable]) 482=item $json = $json->convert_blessed ([$enable])
483
484=item $enabled = $json->get_convert_blessed
334 485
335If C<$enable> is true (or missing), then C<encode>, upon encountering a 486If C<$enable> is true (or missing), then C<encode>, upon encountering a
336blessed object, will check for the availability of the C<TO_JSON> method 487blessed object, will check for the availability of the C<TO_JSON> method
337on the object's class. If found, it will be called in scalar context 488on the object's class. If found, it will be called in scalar context
338and the resulting scalar will be encoded instead of the object. If no 489and the resulting scalar will be encoded instead of the object. If no
342The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON> 493The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
343returns other blessed objects, those will be handled in the same 494returns other blessed objects, those will be handled in the same
344way. C<TO_JSON> must take care of not causing an endless recursion cycle 495way. C<TO_JSON> must take care of not causing an endless recursion cycle
345(== crash) in this case. The name of C<TO_JSON> was chosen because other 496(== crash) in this case. The name of C<TO_JSON> was chosen because other
346methods called by the Perl core (== not by the user of the object) are 497methods called by the Perl core (== not by the user of the object) are
347usually in upper case letters and to avoid collisions with the C<to_json> 498usually in upper case letters and to avoid collisions with any C<to_json>
348function. 499function or method.
349 500
350This setting does not yet influence C<decode> in any way, but in the 501This setting does not yet influence C<decode> in any way, but in the
351future, global hooks might get installed that influence C<decode> and are 502future, global hooks might get installed that influence C<decode> and are
352enabled by this setting. 503enabled by this setting.
353 504
354If C<$enable> is false, then the C<allow_blessed> setting will decide what 505If C<$enable> is false, then the C<allow_blessed> setting will decide what
355to do when a blessed object is found. 506to do when a blessed object is found.
356 507
508=item $json = $json->filter_json_object ([$coderef->($hashref)])
509
510When C<$coderef> is specified, it will be called from C<decode> each
511time it decodes a JSON object. The only argument is a reference to the
512newly-created hash. If the code references returns a single scalar (which
513need not be a reference), this value (i.e. a copy of that scalar to avoid
514aliasing) is inserted into the deserialised data structure. If it returns
515an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
516original deserialised hash will be inserted. This setting can slow down
517decoding considerably.
518
519When C<$coderef> is omitted or undefined, any existing callback will
520be removed and C<decode> will not change the deserialised hash in any
521way.
522
523Example, convert all JSON objects into the integer 5:
524
525 my $js = JSON::XS->new->filter_json_object (sub { 5 });
526 # returns [5]
527 $js->decode ('[{}]')
528 # throw an exception because allow_nonref is not enabled
529 # so a lone 5 is not allowed.
530 $js->decode ('{"a":1, "b":2}');
531
532=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
533
534Works remotely similar to C<filter_json_object>, but is only called for
535JSON objects having a single key named C<$key>.
536
537This C<$coderef> is called before the one specified via
538C<filter_json_object>, if any. It gets passed the single value in the JSON
539object. If it returns a single value, it will be inserted into the data
540structure. If it returns nothing (not even C<undef> but the empty list),
541the callback from C<filter_json_object> will be called next, as if no
542single-key callback were specified.
543
544If C<$coderef> is omitted or undefined, the corresponding callback will be
545disabled. There can only ever be one callback for a given key.
546
547As this callback gets called less often then the C<filter_json_object>
548one, decoding speed will not usually suffer as much. Therefore, single-key
549objects make excellent targets to serialise Perl objects into, especially
550as single-key JSON objects are as close to the type-tagged value concept
551as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
552support this in any way, so you need to make sure your data never looks
553like a serialised Perl hash.
554
555Typical names for the single object key are C<__class_whatever__>, or
556C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
557things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
558with real hashes.
559
560Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
561into the corresponding C<< $WIDGET{<id>} >> object:
562
563 # return whatever is in $WIDGET{5}:
564 JSON::XS
565 ->new
566 ->filter_json_single_key_object (__widget__ => sub {
567 $WIDGET{ $_[0] }
568 })
569 ->decode ('{"__widget__": 5')
570
571 # this can be used with a TO_JSON method in some "widget" class
572 # for serialisation to json:
573 sub WidgetBase::TO_JSON {
574 my ($self) = @_;
575
576 unless ($self->{id}) {
577 $self->{id} = ..get..some..id..;
578 $WIDGET{$self->{id}} = $self;
579 }
580
581 { __widget__ => $self->{id} }
582 }
583
357=item $json = $json->shrink ([$enable]) 584=item $json = $json->shrink ([$enable])
585
586=item $enabled = $json->get_shrink
358 587
359Perl usually over-allocates memory a bit when allocating space for 588Perl usually over-allocates memory a bit when allocating space for
360strings. This flag optionally resizes strings generated by either 589strings. This flag optionally resizes strings generated by either
361C<encode> or C<decode> to their minimum size possible. This can save 590C<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 591memory when your JSON texts are either very very long or you have many
380strings that look like integers or floats into integers or floats 609strings that look like integers or floats into integers or floats
381internally (there is no difference on the Perl level), saving space. 610internally (there is no difference on the Perl level), saving space.
382 611
383=item $json = $json->max_depth ([$maximum_nesting_depth]) 612=item $json = $json->max_depth ([$maximum_nesting_depth])
384 613
614=item $max_depth = $json->get_max_depth
615
385Sets the maximum nesting level (default C<512>) accepted while encoding 616Sets the maximum nesting level (default C<512>) accepted while encoding
386or decoding. If the JSON text or Perl data structure has an equal or 617or decoding. If the JSON text or Perl data structure has an equal or
387higher nesting level then this limit, then the encoder and decoder will 618higher nesting level then this limit, then the encoder and decoder will
388stop and croak at that point. 619stop and croak at that point.
389 620
400used, which is rarely useful. 631used, which is rarely useful.
401 632
402See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 633See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
403 634
404=item $json = $json->max_size ([$maximum_string_size]) 635=item $json = $json->max_size ([$maximum_string_size])
636
637=item $max_size = $json->get_max_size
405 638
406Set the maximum length a JSON text may have (in bytes) where decoding is 639Set the maximum length a JSON text may have (in bytes) where decoding is
407being attempted. The default is C<0>, meaning no limit. When C<decode> 640being attempted. The default is C<0>, meaning no limit. When C<decode>
408is called on a string longer then this number of characters it will not 641is called on a string longer then this number of characters it will not
409attempt to decode the string but throw an exception. This setting has no 642attempt to decode the string but throw an exception. This setting has no
448 => ([], 3) 681 => ([], 3)
449 682
450=back 683=back
451 684
452 685
686=head1 INCREMENTAL PARSING
687
688[This section is still EXPERIMENTAL]
689
690In some cases, there is the need for incremental parsing of JSON
691texts. While this module always has to keep both JSON text and resulting
692Perl data structure in memory at one time, it does allow you to parse a
693JSON stream incrementally. It does so by accumulating text until it has
694a full JSON object, which it then can decode. This process is similar to
695using C<decode_prefix> to see if a full JSON object is available, but is
696much more efficient (JSON::XS will only attempt to parse the JSON text
697once it is sure it has enough text to get a decisive result, using a very
698simple but truly incremental parser).
699
700The following two methods deal with this.
701
702=over 4
703
704=item [void, scalar or list context] = $json->incr_parse ([$string])
705
706This is the central parsing function. It can both append new text and
707extract objects from the stream accumulated so far (both of these
708functions are optional).
709
710If C<$string> is given, then this string is appended to the already
711existing JSON fragment stored in the C<$json> object.
712
713After that, if the function is called in void context, it will simply
714return without doing anything further. This can be used to add more text
715in as many chunks as you want.
716
717If the method is called in scalar context, then it will try to extract
718exactly I<one> JSON object. If that is successful, it will return this
719object, otherwise it will return C<undef>. This is the most common way of
720using the method.
721
722And finally, in list context, it will try to extract as many objects
723from the stream as it can find and return them, or the empty list
724otherwise. For this to work, there must be no separators between the JSON
725objects or arrays, instead they must be concatenated back-to-back.
726
727=item $lvalue_string = $json->incr_text
728
729This method returns the currently stored JSON fragment as an lvalue, that
730is, you can manipulate it. This I<only> works when a preceding call to
731C<incr_parse> in I<scalar context> successfully returned an object. Under
732all other circumstances you must not call this function (I mean it.
733although in simple tests it might actually work, it I<will> fail under
734real world conditions). As a special exception, you can also call this
735method before having parsed anything.
736
737This function is useful in two cases: a) finding the trailing text after a
738JSON object or b) parsing multiple JSON objects separated by non-JSON text
739(such as commas).
740
741=back
742
743=head2 LIMITATIONS
744
745All options that affect decoding are supported, except
746C<allow_nonref>. The reason for this is that it cannot be made to
747work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
748them back to back and still decode them perfectly. This does not hold true
749for JSON numbers, however.
750
751For example, is the string C<1> a single JSON number, or is it simply the
752start of C<12>? Or is C<12> a single JSON number, or the concatenation
753of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
754takes the conservative route and disallows this case.
755
756=head2 EXAMPLES
757
758Some examples will make all this clearer. First, a simple example that
759works similarly to C<decode_prefix>: We want to decode the JSON object at
760the start of a string and identify the portion after the JSON object:
761
762 my $text = "[1,2,3] hello";
763
764 my $json = new JSON::XS;
765
766 my $obj = $json->incr_parse ($text)
767 or die "expected JSON object or array at beginning of string";
768
769 my $tail = $json->incr_text;
770 # $tail now contains " hello"
771
772Easy, isn't it?
773
774Now for a more complicated example: Imagine a hypothetical protocol where
775you read some requests from a TCP stream, and each request is a JSON
776array, without any separation between them (in fact, it is often useful to
777use newlines as "separators", as these get interpreted as whitespace at
778the start of the JSON text, which makes it possible to test said protocol
779with C<telnet>...).
780
781Here is how you'd do it (it is trivial to write this in an event-based
782manner):
783
784 my $json = new JSON::XS;
785
786 # read some data from the socket
787 while (sysread $socket, my $buf, 4096) {
788
789 # split and decode as many requests as possible
790 for my $request ($json->incr_parse ($buf)) {
791 # act on the $request
792 }
793 }
794
795Another complicated example: Assume you have a string with JSON objects
796or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
797[3]>). To parse them, we have to skip the commas between the JSON texts,
798and here is where the lvalue-ness of C<incr_text> comes in useful:
799
800 my $text = "[1],[2], [3]";
801 my $json = new JSON::XS;
802
803 # void context, so no parsing done
804 $json->incr_parse ($text);
805
806 # now extract as many objects as possible. note the
807 # use of scalar context so incr_text can be called.
808 while (my $obj = $json->incr_parse) {
809 # do something with $obj
810
811 # now skip the optional comma
812 $json->incr_text =~ s/^ \s* , //x;
813 }
814
815Now lets go for a very complex example: Assume that you have a gigantic
816JSON array-of-objects, many gigabytes in size, and you want to parse it,
817but you cannot load it into memory fully (this has actually happened in
818the real world :).
819
820Well, you lost, you have to implement your own JSON parser. But JSON::XS
821can still help you: You implement a (very simple) array parser and let
822JSON decode the array elements, which are all full JSON objects on their
823own (this wouldn't work if the array elements could be JSON numbers, for
824example):
825
826 my $json = new JSON::XS;
827
828 # open the monster
829 open my $fh, "<bigfile.json"
830 or die "bigfile: $!";
831
832 # first parse the initial "["
833 for (;;) {
834 sysread $fh, my $buf, 65536
835 or die "read error: $!";
836 $json->incr_parse ($buf); # void context, so no parsing
837
838 # Exit the loop once we found and removed(!) the initial "[".
839 # In essence, we are (ab-)using the $json object as a simple scalar
840 # we append data to.
841 last if $json->incr_text =~ s/^ \s* \[ //x;
842 }
843
844 # now we have the skipped the initial "[", so continue
845 # parsing all the elements.
846 for (;;) {
847 # in this loop we read data until we got a single JSON object
848 for (;;) {
849 if (my $obj = $json->incr_parse) {
850 # do something with $obj
851 last;
852 }
853
854 # add more data
855 sysread $fh, my $buf, 65536
856 or die "read error: $!";
857 $json->incr_parse ($buf); # void context, so no parsing
858 }
859
860 # in this loop we read data until we either found and parsed the
861 # separating "," between elements, or the final "]"
862 for (;;) {
863 # first skip whitespace
864 $json->incr_text =~ s/^\s*//;
865
866 # if we find "]", we are done
867 if ($json->incr_text =~ s/^\]//) {
868 print "finished.\n";
869 exit;
870 }
871
872 # if we find ",", we can continue with the next element
873 if ($json->incr_text =~ s/^,//) {
874 last;
875 }
876
877 # if we find anything else, we have a parse error!
878 if (length $json->incr_text) {
879 die "parse error near ", $json->incr_text;
880 }
881
882 # else add more data
883 sysread $fh, my $buf, 65536
884 or die "read error: $!";
885 $json->incr_parse ($buf); # void context, so no parsing
886 }
887
888This is a complex example, but most of the complexity comes from the fact
889that we are trying to be correct (bear with me if I am wrong, I never ran
890the above example :).
891
892
893
453=head1 MAPPING 894=head1 MAPPING
454 895
455This section describes how JSON::XS maps Perl values to JSON values and 896This section describes how JSON::XS maps Perl values to JSON values and
456vice versa. These mappings are designed to "do the right thing" in most 897vice versa. These mappings are designed to "do the right thing" in most
457circumstances automatically, preserving round-tripping characteristics 898circumstances automatically, preserving round-tripping characteristics
458(what you put in comes out as something equivalent). 899(what you put in comes out as something equivalent).
459 900
460For the more enlightened: note that in the following descriptions, 901For the more enlightened: note that in the following descriptions,
461lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl> 902lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
462refers to the abstract Perl language itself. 903refers to the abstract Perl language itself.
463 904
464 905
465=head2 JSON -> PERL 906=head2 JSON -> PERL
466 907
467=over 4 908=over 4
468 909
469=item object 910=item object
470 911
471A JSON object becomes a reference to a hash in Perl. No ordering of object 912A JSON object becomes a reference to a hash in Perl. No ordering of object
472keys is preserved (JSON does not preserver object key ordering itself). 913keys is preserved (JSON does not preserve object key ordering itself).
473 914
474=item array 915=item array
475 916
476A JSON array becomes a reference to an array in Perl. 917A JSON array becomes a reference to an array in Perl.
477 918
481are represented by the same codepoints in the Perl string, so no manual 922are represented by the same codepoints in the Perl string, so no manual
482decoding is necessary. 923decoding is necessary.
483 924
484=item number 925=item number
485 926
486A JSON number becomes either an integer or numeric (floating point) 927A JSON number becomes either an integer, numeric (floating point) or
487scalar in perl, depending on its range and any fractional parts. On the 928string scalar in perl, depending on its range and any fractional parts. On
488Perl level, there is no difference between those as Perl handles all the 929the Perl level, there is no difference between those as Perl handles all
489conversion details, but an integer may take slightly less memory and might 930the conversion details, but an integer may take slightly less memory and
490represent more values exactly than (floating point) numbers. 931might represent more values exactly than floating point numbers.
932
933If the number consists of digits only, JSON::XS will try to represent
934it as an integer value. If that fails, it will try to represent it as
935a numeric (floating point) value if that is possible without loss of
936precision. Otherwise it will preserve the number as a string value (in
937which case you lose roundtripping ability, as the JSON number will be
938re-encoded toa JSON string).
939
940Numbers containing a fractional or exponential part will always be
941represented as numeric (floating point) values, possibly at a loss of
942precision (in which case you might lose perfect roundtripping ability, but
943the JSON number will still be re-encoded as a JSON number).
491 944
492=item true, false 945=item true, false
493 946
494These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, 947These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
495respectively. They are overloaded to act almost exactly like the numbers 948respectively. They are overloaded to act almost exactly like the numbers
496C<1> and C<0>. You can check wether a scalar is a JSON boolean by using 949C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
497the C<JSON::XS::is_bool> function. 950the C<JSON::XS::is_bool> function.
498 951
499=item null 952=item null
500 953
501A JSON null atom becomes C<undef> in Perl. 954A JSON null atom becomes C<undef> in Perl.
532Other unblessed references are generally not allowed and will cause an 985Other unblessed references are generally not allowed and will cause an
533exception to be thrown, except for references to the integers C<0> and 986exception to be thrown, except for references to the integers C<0> and
534C<1>, which get turned into C<false> and C<true> atoms in JSON. You can 987C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
535also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. 988also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
536 989
537 to_json [\0,JSON::XS::true] # yields [false,true] 990 encode_json [\0,JSON::XS::true] # yields [false,true]
538 991
539=item JSON::XS::true, JSON::XS::false 992=item JSON::XS::true, JSON::XS::false
540 993
541These special values become JSON true and JSON false values, 994These special values become JSON true and JSON false values,
542respectively. You cna alos use C<\1> and C<\0> directly if you want. 995respectively. You can also use C<\1> and C<\0> directly if you want.
543 996
544=item blessed objects 997=item blessed objects
545 998
546Blessed objects are not allowed. JSON::XS currently tries to encode their 999Blessed objects are not directly representable in JSON. See the
547underlying representation (hash- or arrayref), but this behaviour might 1000C<allow_blessed> and C<convert_blessed> methods on various options on
548change in future versions. 1001how to deal with this: basically, you can choose between throwing an
1002exception, encoding the reference as if it weren't blessed, or provide
1003your own serialiser method.
549 1004
550=item simple scalars 1005=item simple scalars
551 1006
552Simple Perl scalars (any scalar that is not a reference) are the most 1007Simple Perl scalars (any scalar that is not a reference) are the most
553difficult objects to encode: JSON::XS will encode undefined scalars as 1008difficult objects to encode: JSON::XS will encode undefined scalars as
554JSON null value, scalars that have last been used in a string context 1009JSON C<null> values, scalars that have last been used in a string context
555before encoding as JSON strings and anything else as number value: 1010before encoding as JSON strings, and anything else as number value:
556 1011
557 # dump as number 1012 # dump as number
558 to_json [2] # yields [2] 1013 encode_json [2] # yields [2]
559 to_json [-3.0e17] # yields [-3e+17] 1014 encode_json [-3.0e17] # yields [-3e+17]
560 my $value = 5; to_json [$value] # yields [5] 1015 my $value = 5; encode_json [$value] # yields [5]
561 1016
562 # used as string, so dump as string 1017 # used as string, so dump as string
563 print $value; 1018 print $value;
564 to_json [$value] # yields ["5"] 1019 encode_json [$value] # yields ["5"]
565 1020
566 # undef becomes null 1021 # undef becomes null
567 to_json [undef] # yields [null] 1022 encode_json [undef] # yields [null]
568 1023
569You can force the type to be a string by stringifying it: 1024You can force the type to be a JSON string by stringifying it:
570 1025
571 my $x = 3.1; # some variable containing a number 1026 my $x = 3.1; # some variable containing a number
572 "$x"; # stringified 1027 "$x"; # stringified
573 $x .= ""; # another, more awkward way to stringify 1028 $x .= ""; # another, more awkward way to stringify
574 print $x; # perl does it for you, too, quite often 1029 print $x; # perl does it for you, too, quite often
575 1030
576You can force the type to be a number by numifying it: 1031You can force the type to be a JSON number by numifying it:
577 1032
578 my $x = "3"; # some variable containing a string 1033 my $x = "3"; # some variable containing a string
579 $x += 0; # numify it, ensuring it will be dumped as a number 1034 $x += 0; # numify it, ensuring it will be dumped as a number
580 $x *= 1; # same thing, the choise is yours. 1035 $x *= 1; # same thing, the choice is yours.
581 1036
582You can not currently output JSON booleans or force the type in other, 1037You can not currently force the type in other, less obscure, ways. Tell me
583less obscure, ways. Tell me if you need this capability. 1038if you need this capability (but don't forget to explain why it's needed
1039:).
1040
1041=back
1042
1043
1044=head1 ENCODING/CODESET FLAG NOTES
1045
1046The interested reader might have seen a number of flags that signify
1047encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
1048some confusion on what these do, so here is a short comparison:
1049
1050C<utf8> controls whether the JSON text created by C<encode> (and expected
1051by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
1052control whether C<encode> escapes character values outside their respective
1053codeset range. Neither of these flags conflict with each other, although
1054some combinations make less sense than others.
1055
1056Care has been taken to make all flags symmetrical with respect to
1057C<encode> and C<decode>, that is, texts encoded with any combination of
1058these flag values will be correctly decoded when the same flags are used
1059- in general, if you use different flag settings while encoding vs. when
1060decoding you likely have a bug somewhere.
1061
1062Below comes a verbose discussion of these flags. Note that a "codeset" is
1063simply an abstract set of character-codepoint pairs, while an encoding
1064takes those codepoint numbers and I<encodes> them, in our case into
1065octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
1066and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
1067the same time, which can be confusing.
1068
1069=over 4
1070
1071=item C<utf8> flag disabled
1072
1073When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
1074and expect Unicode strings, that is, characters with high ordinal Unicode
1075values (> 255) will be encoded as such characters, and likewise such
1076characters are decoded as-is, no canges to them will be done, except
1077"(re-)interpreting" them as Unicode codepoints or Unicode characters,
1078respectively (to Perl, these are the same thing in strings unless you do
1079funny/weird/dumb stuff).
1080
1081This is useful when you want to do the encoding yourself (e.g. when you
1082want to have UTF-16 encoded JSON texts) or when some other layer does
1083the encoding for you (for example, when printing to a terminal using a
1084filehandle that transparently encodes to UTF-8 you certainly do NOT want
1085to UTF-8 encode your data first and have Perl encode it another time).
1086
1087=item C<utf8> flag enabled
1088
1089If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
1090characters using the corresponding UTF-8 multi-byte sequence, and will
1091expect your input strings to be encoded as UTF-8, that is, no "character"
1092of the input string must have any value > 255, as UTF-8 does not allow
1093that.
1094
1095The C<utf8> flag therefore switches between two modes: disabled means you
1096will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
1097octet/binary string in Perl.
1098
1099=item C<latin1> or C<ascii> flags enabled
1100
1101With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
1102with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
1103characters as specified by the C<utf8> flag.
1104
1105If C<utf8> is disabled, then the result is also correctly encoded in those
1106character sets (as both are proper subsets of Unicode, meaning that a
1107Unicode string with all character values < 256 is the same thing as a
1108ISO-8859-1 string, and a Unicode string with all character values < 128 is
1109the same thing as an ASCII string in Perl).
1110
1111If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
1112regardless of these flags, just some more characters will be escaped using
1113C<\uXXXX> then before.
1114
1115Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
1116encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
1117encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
1118a subset of Unicode), while ASCII is.
1119
1120Surprisingly, C<decode> will ignore these flags and so treat all input
1121values as governed by the C<utf8> flag. If it is disabled, this allows you
1122to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
1123Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
1124
1125So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
1126they only govern when the JSON output engine escapes a character or not.
1127
1128The main use for C<latin1> is to relatively efficiently store binary data
1129as JSON, at the expense of breaking compatibility with most JSON decoders.
1130
1131The main use for C<ascii> is to force the output to not contain characters
1132with values > 127, which means you can interpret the resulting string
1133as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
11348-bit-encoding, and still get the same data structure back. This is useful
1135when your channel for JSON transfer is not 8-bit clean or the encoding
1136might be mangled in between (e.g. in mail), and works because ASCII is a
1137proper subset of most 8-bit and multibyte encodings in use in the world.
584 1138
585=back 1139=back
586 1140
587 1141
588=head1 COMPARISON 1142=head1 COMPARISON
593followed by some benchmark values. JSON::XS was designed not to suffer 1147followed by some benchmark values. JSON::XS was designed not to suffer
594from any of these problems or limitations. 1148from any of these problems or limitations.
595 1149
596=over 4 1150=over 4
597 1151
1152=item JSON 2.xx
1153
1154A marvellous piece of engineering, this module either uses JSON::XS
1155directly when available (so will be 100% compatible with it, including
1156speed), or it uses JSON::PP, which is basically JSON::XS translated to
1157Pure Perl, which should be 100% compatible with JSON::XS, just a bit
1158slower.
1159
1160You cannot really lose by using this module, especially as it tries very
1161hard to work even with ancient Perl versions, while JSON::XS does not.
1162
598=item JSON 1.07 1163=item JSON 1.07
599 1164
600Slow (but very portable, as it is written in pure Perl). 1165Slow (but very portable, as it is written in pure Perl).
601 1166
602Undocumented/buggy Unicode handling (how JSON handles unicode values is 1167Undocumented/buggy Unicode handling (how JSON handles Unicode values is
603undocumented. One can get far by feeding it unicode strings and doing 1168undocumented. One can get far by feeding it Unicode strings and doing
604en-/decoding oneself, but unicode escapes are not working properly). 1169en-/decoding oneself, but Unicode escapes are not working properly).
605 1170
606No roundtripping (strings get clobbered if they look like numbers, e.g. 1171No round-tripping (strings get clobbered if they look like numbers, e.g.
607the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will 1172the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
608decode into the number 2. 1173decode into the number 2.
609 1174
610=item JSON::PC 0.01 1175=item JSON::PC 0.01
611 1176
612Very fast. 1177Very fast.
613 1178
614Undocumented/buggy Unicode handling. 1179Undocumented/buggy Unicode handling.
615 1180
616No roundtripping. 1181No round-tripping.
617 1182
618Has problems handling many Perl values (e.g. regex results and other magic 1183Has problems handling many Perl values (e.g. regex results and other magic
619values will make it croak). 1184values will make it croak).
620 1185
621Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> 1186Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
631Very inflexible (no human-readable format supported, format pretty much 1196Very inflexible (no human-readable format supported, format pretty much
632undocumented. I need at least a format for easy reading by humans and a 1197undocumented. I need at least a format for easy reading by humans and a
633single-line compact format for use in a protocol, and preferably a way to 1198single-line compact format for use in a protocol, and preferably a way to
634generate ASCII-only JSON texts). 1199generate ASCII-only JSON texts).
635 1200
636Completely broken (and confusingly documented) Unicode handling (unicode 1201Completely broken (and confusingly documented) Unicode handling (Unicode
637escapes are not working properly, you need to set ImplicitUnicode to 1202escapes are not working properly, you need to set ImplicitUnicode to
638I<different> values on en- and decoding to get symmetric behaviour). 1203I<different> values on en- and decoding to get symmetric behaviour).
639 1204
640No roundtripping (simple cases work, but this depends on wether the scalar 1205No round-tripping (simple cases work, but this depends on whether the scalar
641value was used in a numeric context or not). 1206value was used in a numeric context or not).
642 1207
643Dumping hashes may skip hash values depending on iterator state. 1208Dumping hashes may skip hash values depending on iterator state.
644 1209
645Unmaintained (maintainer unresponsive for many months, bugs are not 1210Unmaintained (maintainer unresponsive for many months, bugs are not
646getting fixed). 1211getting fixed).
647 1212
648Does not check input for validity (i.e. will accept non-JSON input and 1213Does not check input for validity (i.e. will accept non-JSON input and
649return "something" instead of raising an exception. This is a security 1214return "something" instead of raising an exception. This is a security
650issue: imagine two banks transfering money between each other using 1215issue: imagine two banks transferring money between each other using
651JSON. One bank might parse a given non-JSON request and deduct money, 1216JSON. One bank might parse a given non-JSON request and deduct money,
652while the other might reject the transaction with a syntax error. While a 1217while the other might reject the transaction with a syntax error. While a
653good protocol will at least recover, that is extra unnecessary work and 1218good protocol will at least recover, that is extra unnecessary work and
654the transaction will still not succeed). 1219the transaction will still not succeed).
655 1220
656=item JSON::DWIW 0.04 1221=item JSON::DWIW 0.04
657 1222
658Very fast. Very natural. Very nice. 1223Very fast. Very natural. Very nice.
659 1224
660Undocumented unicode handling (but the best of the pack. Unicode escapes 1225Undocumented Unicode handling (but the best of the pack. Unicode escapes
661still don't get parsed properly). 1226still don't get parsed properly).
662 1227
663Very inflexible. 1228Very inflexible.
664 1229
665No roundtripping. 1230No round-tripping.
666 1231
667Does not generate valid JSON texts (key strings are often unquoted, empty keys 1232Does not generate valid JSON texts (key strings are often unquoted, empty keys
668result in nothing being output) 1233result in nothing being output)
669 1234
670Does not check input for validity. 1235Does not check input for validity.
672=back 1237=back
673 1238
674 1239
675=head2 JSON and YAML 1240=head2 JSON and YAML
676 1241
677You often hear that JSON is a subset (or a close subset) of YAML. This is, 1242You often hear that JSON is a subset of YAML. This is, however, a mass
678however, a mass hysteria and very far from the truth. In general, there is 1243hysteria(*) and very far from the truth (as of the time of this writing),
679no way to configure JSON::XS to output a data structure as valid YAML. 1244so let me state it clearly: I<in general, there is no way to configure
1245JSON::XS to output a data structure as valid YAML> that works in all
1246cases.
680 1247
681If you really must use JSON::XS to generate YAML, you should use this 1248If you really must use JSON::XS to generate YAML, you should use this
682algorithm (subject to change in future versions): 1249algorithm (subject to change in future versions):
683 1250
684 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1251 my $to_yaml = JSON::XS->new->utf8->space_after (1);
685 my $yaml = $to_yaml->encode ($ref) . "\n"; 1252 my $yaml = $to_yaml->encode ($ref) . "\n";
686 1253
687This will usually generate JSON texts that also parse as valid 1254This will I<usually> generate JSON texts that also parse as valid
688YAML. Please note that YAML has hardcoded limits on (simple) object key 1255YAML. Please note that YAML has hardcoded limits on (simple) object key
689lengths that JSON doesn't have, so you should make sure that your hash 1256lengths that JSON doesn't have and also has different and incompatible
1257unicode handling, so you should make sure that your hash keys are
690keys are noticably shorter than the 1024 characters YAML allows. 1258noticeably shorter than the 1024 "stream characters" YAML allows and that
1259you do not have characters with codepoint values outside the Unicode BMP
1260(basic multilingual page). YAML also does not allow C<\/> sequences in
1261strings (which JSON::XS does not I<currently> generate, but other JSON
1262generators might).
691 1263
692There might be other incompatibilities that I am not aware of. In general 1264There might be other incompatibilities that I am not aware of (or the YAML
1265specification has been changed yet again - it does so quite often). In
693you should not try to generate YAML with a JSON generator or vice versa, 1266general you should not try to generate YAML with a JSON generator or vice
694or try to parse JSON with a YAML parser or vice versa: chances are high 1267versa, or try to parse JSON with a YAML parser or vice versa: chances are
695that you will run into severe interoperability problems. 1268high that you will run into severe interoperability problems when you
1269least expect it.
1270
1271=over 4
1272
1273=item (*)
1274
1275I have been pressured multiple times by Brian Ingerson (one of the
1276authors of the YAML specification) to remove this paragraph, despite him
1277acknowledging that the actual incompatibilities exist. As I was personally
1278bitten by this "JSON is YAML" lie, I refused and said I will continue to
1279educate people about these issues, so others do not run into the same
1280problem again and again. After this, Brian called me a (quote)I<complete
1281and worthless idiot>(unquote).
1282
1283In my opinion, instead of pressuring and insulting people who actually
1284clarify issues with YAML and the wrong statements of some of its
1285proponents, I would kindly suggest reading the JSON spec (which is not
1286that difficult or long) and finally make YAML compatible to it, and
1287educating users about the changes, instead of spreading lies about the
1288real compatibility for many I<years> and trying to silence people who
1289point out that it isn't true.
1290
1291=back
696 1292
697 1293
698=head2 SPEED 1294=head2 SPEED
699 1295
700It seems that JSON::XS is surprisingly fast, as shown in the following 1296It seems that JSON::XS is surprisingly fast, as shown in the following
701tables. They have been generated with the help of the C<eg/bench> program 1297tables. They have been generated with the help of the C<eg/bench> program
702in the JSON::XS distribution, to make it easy to compare on your own 1298in the JSON::XS distribution, to make it easy to compare on your own
703system. 1299system.
704 1300
705First comes a comparison between various modules using a very short 1301First comes a comparison between various modules using
706single-line JSON string: 1302a very short single-line JSON string (also available at
1303L<http://dist.schmorp.de/misc/json/short.json>).
707 1304
708 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1305 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
709 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1306 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
710 1307
711It shows the number of encodes/decodes per second (JSON::XS uses 1308It shows the number of encodes/decodes per second (JSON::XS uses
713with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables 1310with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
714shrink). Higher is better: 1311shrink). Higher is better:
715 1312
716 module | encode | decode | 1313 module | encode | decode |
717 -----------|------------|------------| 1314 -----------|------------|------------|
718 JSON | 7645.468 | 4208.613 | 1315 JSON 1.x | 4990.842 | 4088.813 |
719 JSON::DWIW | 40721.398 | 77101.176 | 1316 JSON::DWIW | 51653.990 | 71575.154 |
720 JSON::PC | 65948.176 | 78251.940 | 1317 JSON::PC | 65948.176 | 74631.744 |
721 JSON::Syck | 22844.793 | 26479.192 | 1318 JSON::PP | 8931.652 | 3817.168 |
1319 JSON::Syck | 24877.248 | 27776.848 |
722 JSON::XS | 388361.481 | 199728.762 | 1320 JSON::XS | 388361.481 | 227951.304 |
723 JSON::XS/2 | 218453.333 | 192399.266 | 1321 JSON::XS/2 | 227951.304 | 218453.333 |
724 JSON::XS/3 | 338250.323 | 192399.266 | 1322 JSON::XS/3 | 338250.323 | 218453.333 |
725 Storable | 15779.925 | 14169.946 | 1323 Storable | 16500.016 | 135300.129 |
726 -----------+------------+------------+ 1324 -----------+------------+------------+
727 1325
728That is, JSON::XS is about five times faster than JSON::DWIW on encoding, 1326That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
729about three times faster on decoding, and over fourty times faster 1327about three times faster on decoding, and over forty times faster
730than JSON, even with pretty-printing and key sorting. It also compares 1328than JSON, even with pretty-printing and key sorting. It also compares
731favourably to Storable for small amounts of data. 1329favourably to Storable for small amounts of data.
732 1330
733Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1331Using a longer test string (roughly 18KB, generated from Yahoo! Locals
734search API (http://nanoref.com/yahooapis/mgPdGg): 1332search API (L<http://dist.schmorp.de/misc/json/long.json>).
735 1333
736 module | encode | decode | 1334 module | encode | decode |
737 -----------|------------|------------| 1335 -----------|------------|------------|
738 JSON | 254.685 | 37.665 | 1336 JSON 1.x | 55.260 | 34.971 |
739 JSON::DWIW | 843.343 | 1049.731 | 1337 JSON::DWIW | 825.228 | 1082.513 |
740 JSON::PC | 3602.116 | 2307.352 | 1338 JSON::PC | 3571.444 | 2394.829 |
1339 JSON::PP | 210.987 | 32.574 |
741 JSON::Syck | 505.107 | 787.899 | 1340 JSON::Syck | 552.551 | 787.544 |
742 JSON::XS | 5747.196 | 3690.220 | 1341 JSON::XS | 5780.463 | 4854.519 |
743 JSON::XS/2 | 3968.121 | 3676.634 | 1342 JSON::XS/2 | 3869.998 | 4798.975 |
744 JSON::XS/3 | 6105.246 | 3662.508 | 1343 JSON::XS/3 | 5862.880 | 4798.975 |
745 Storable | 4417.337 | 5285.161 | 1344 Storable | 4445.002 | 5235.027 |
746 -----------+------------+------------+ 1345 -----------+------------+------------+
747 1346
748Again, JSON::XS leads by far (except for Storable which non-surprisingly 1347Again, JSON::XS leads by far (except for Storable which non-surprisingly
749decodes faster). 1348decodes faster).
750 1349
751On large strings containing lots of high unicode characters, some modules 1350On 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 1351(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 1352will be broken due to missing (or wrong) Unicode handling. Others refuse
754to decode or encode properly, so it was impossible to prepare a fair 1353to decode or encode properly, so it was impossible to prepare a fair
755comparison table for that case. 1354comparison table for that case.
756 1355
757 1356
758=head1 SECURITY CONSIDERATIONS 1357=head1 SECURITY CONSIDERATIONS
764any buffer overflows. Obviously, this module should ensure that and I am 1363any buffer overflows. Obviously, this module should ensure that and I am
765trying hard on making that true, but you never know. 1364trying hard on making that true, but you never know.
766 1365
767Second, you need to avoid resource-starving attacks. That means you should 1366Second, 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 1367limit 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 1368resources 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 1369can 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 1370usually 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 1371it 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 1372text, 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. 1373might want to check the size before you accept the string.
775 1374
776Third, JSON::XS recurses using the C stack when decoding objects and 1375Third, JSON::XS recurses using the C stack when decoding objects and
777arrays. The C stack is a limited resource: for instance, on my amd64 1376arrays. The C stack is a limited resource: for instance, on my amd64
778machine with 8MB of stack size I can decode around 180k nested arrays but 1377machine with 8MB of stack size I can decode around 180k nested arrays but
779only 14k nested JSON objects (due to perl itself recursing deeply on croak 1378only 14k nested JSON objects (due to perl itself recursing deeply on croak
780to free the temporary). If that is exceeded, the program crashes. to be 1379to free the temporary). If that is exceeded, the program crashes. To be
781conservative, the default nesting limit is set to 512. If your process 1380conservative, the default nesting limit is set to 512. If your process
782has a smaller stack, you should adjust this setting accordingly with the 1381has a smaller stack, you should adjust this setting accordingly with the
783C<max_depth> method. 1382C<max_depth> method.
784 1383
785And last but least, something else could bomb you that I forgot to think 1384Something else could bomb you, too, that I forgot to think of. In that
786of. In that case, you get to keep the pieces. I am always open for hints, 1385case, you get to keep the pieces. I am always open for hints, though...
787though... 1386
1387Also keep in mind that JSON::XS might leak contents of your Perl data
1388structures in its error messages, so when you serialise sensitive
1389information you might want to make sure that exceptions thrown by JSON::XS
1390will not end up in front of untrusted eyes.
788 1391
789If you are using JSON::XS to return packets to consumption 1392If you are using JSON::XS to return packets to consumption
790by javascript scripts in a browser you should have a look at 1393by JavaScript scripts in a browser you should have a look at
791L<http://jpsykes.com/47/practical-csrf-and-json-security> to see wether 1394L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
792you are vulnerable to some common attack vectors (which really are browser 1395you 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 1396design 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 1397browser developers care only for features, not about getting security
795right). 1398right).
796 1399
797 1400
1401=head1 THREADS
1402
1403This module is I<not> guaranteed to be thread safe and there are no
1404plans to change this until Perl gets thread support (as opposed to the
1405horribly slow so-called "threads" which are simply slow and bloated
1406process simulations - use fork, it's I<much> faster, cheaper, better).
1407
1408(It might actually work, but you have been warned).
1409
1410
798=head1 BUGS 1411=head1 BUGS
799 1412
800While the goal of this module is to be correct, that unfortunately does 1413While 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 1414not mean it's 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 1415still relatively early in its development. If you keep reporting bugs they
803will be fixed swiftly, though. 1416will be fixed swiftly, though.
1417
1418Please refrain from using rt.cpan.org or any other bug reporting
1419service. I put the contact address into my modules for a reason.
804 1420
805=cut 1421=cut
806 1422
807our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" }; 1423our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
808our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" }; 1424our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
825 "--" => sub { $_[0] = ${$_[0]} - 1 }, 1441 "--" => sub { $_[0] = ${$_[0]} - 1 },
826 fallback => 1; 1442 fallback => 1;
827 1443
8281; 14441;
829 1445
1446=head1 SEE ALSO
1447
1448The F<json_xs> command line utility for quick experiments.
1449
830=head1 AUTHOR 1450=head1 AUTHOR
831 1451
832 Marc Lehmann <schmorp@schmorp.de> 1452 Marc Lehmann <schmorp@schmorp.de>
833 http://home.schmorp.de/ 1453 http://home.schmorp.de/
834 1454

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