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Revision 1.47 by root, Mon Jun 25 06:57:42 2007 UTC vs.
Revision 1.111 by root, Mon Jul 21 02:45:17 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
35reports for other reasons. 52reports for other reasons.
36 53
37See COMPARISON, below, for a comparison to some other JSON modules.
38
39See MAPPING, below, on how JSON::XS maps perl values to JSON values and 54See MAPPING, below, on how JSON::XS maps perl values to JSON values and
40vice versa. 55vice versa.
41 56
42=head2 FEATURES 57=head2 FEATURES
43 58
44=over 4 59=over 4
45 60
46=item * correct unicode handling 61=item * correct Unicode handling
47 62
48This module knows how to handle Unicode, and even documents how and when 63This module knows how to handle Unicode, documents how and when it does
49it does so. 64so, and even documents what "correct" means.
50 65
51=item * round-trip integrity 66=item * round-trip integrity
52 67
53When you serialise a perl data structure using only datatypes supported 68When you serialise a perl data structure using only data types supported
54by JSON, the deserialised data structure is identical on the Perl level. 69by 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 70(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
56like a number). 71like a number). There minor I<are> exceptions to this, read the MAPPING
72section below to learn about those.
57 73
58=item * strict checking of JSON correctness 74=item * strict checking of JSON correctness
59 75
60There is no guessing, no generating of illegal JSON texts by default, 76There 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 77and only JSON is accepted as input by default (the latter is a security
62feature). 78feature).
63 79
64=item * fast 80=item * fast
65 81
66Compared to other JSON modules, this module compares favourably in terms 82Compared to other JSON modules and other serialisers such as Storable,
67of speed, too. 83this module usually compares favourably in terms of speed, too.
68 84
69=item * simple to use 85=item * simple to use
70 86
71This module has both a simple functional interface as well as an OO 87This module has both a simple functional interface as well as an object
72interface. 88oriented interface interface.
73 89
74=item * reasonably versatile output formats 90=item * reasonably versatile output formats
75 91
76You can choose between the most compact guarenteed single-line format 92You can choose between the most compact guaranteed-single-line format
77possible (nice for simple line-based protocols), a pure-ascii format 93possible (nice for simple line-based protocols), a pure-ASCII format
78(for when your transport is not 8-bit clean, still supports the whole 94(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 95Unicode 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. 96stuff). Or you can combine those features in whatever way you like.
81 97
82=back 98=back
83 99
84=cut 100=cut
85 101
86package JSON::XS; 102package JSON::XS;
87 103
104no warnings;
88use strict; 105use strict;
89 106
90our $VERSION = '1.4'; 107our $VERSION = '2.2222';
91our @ISA = qw(Exporter); 108our @ISA = qw(Exporter);
92 109
93our @EXPORT = qw(to_json from_json objToJson jsonToObj); 110our @EXPORT = qw(encode_json decode_json to_json from_json);
111
112sub to_json($) {
113 require Carp;
114 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");
115}
116
117sub from_json($) {
118 require Carp;
119 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");
120}
94 121
95use Exporter; 122use Exporter;
96use XSLoader; 123use XSLoader;
97 124
98=head1 FUNCTIONAL INTERFACE 125=head1 FUNCTIONAL INTERFACE
99 126
100The following convinience methods are provided by this module. They are 127The following convenience methods are provided by this module. They are
101exported by default: 128exported by default:
102 129
103=over 4 130=over 4
104 131
105=item $json_text = to_json $perl_scalar 132=item $json_text = encode_json $perl_scalar
106 133
107Converts the given Perl data structure (a simple scalar or a reference to 134Converts 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 135(that is, the string contains octets only). Croaks on error.
109octets only). Croaks on error.
110 136
111This function call is functionally identical to: 137This function call is functionally identical to:
112 138
113 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 139 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
114 140
115except being faster. 141Except being faster.
116 142
117=item $perl_scalar = from_json $json_text 143=item $perl_scalar = decode_json $json_text
118 144
119The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to 145The 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 146to parse that as an UTF-8 encoded JSON text, returning the resulting
121scalar or reference. Croaks on error. 147reference. Croaks on error.
122 148
123This function call is functionally identical to: 149This function call is functionally identical to:
124 150
125 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 151 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
126 152
127except being faster. 153Except being faster.
128 154
129=item $is_boolean = JSON::XS::is_bool $scalar 155=item $is_boolean = JSON::XS::is_bool $scalar
130 156
131Returns true if the passed scalar represents either JSON::XS::true or 157Returns 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 158JSON::XS::false, two constants that act like C<1> and C<0>, respectively
136Perl. 162Perl.
137 163
138=back 164=back
139 165
140 166
167=head1 A FEW NOTES ON UNICODE AND PERL
168
169Since this often leads to confusion, here are a few very clear words on
170how Unicode works in Perl, modulo bugs.
171
172=over 4
173
174=item 1. Perl strings can store characters with ordinal values > 255.
175
176This enables you to store Unicode characters as single characters in a
177Perl string - very natural.
178
179=item 2. Perl does I<not> associate an encoding with your strings.
180
181... until you force it to, e.g. when matching it against a regex, or
182printing the scalar to a file, in which case Perl either interprets your
183string as locale-encoded text, octets/binary, or as Unicode, depending
184on various settings. In no case is an encoding stored together with your
185data, it is I<use> that decides encoding, not any magical meta data.
186
187=item 3. The internal utf-8 flag has no meaning with regards to the
188encoding of your string.
189
190Just ignore that flag unless you debug a Perl bug, a module written in
191XS or want to dive into the internals of perl. Otherwise it will only
192confuse you, as, despite the name, it says nothing about how your string
193is encoded. You can have Unicode strings with that flag set, with that
194flag clear, and you can have binary data with that flag set and that flag
195clear. Other possibilities exist, too.
196
197If you didn't know about that flag, just the better, pretend it doesn't
198exist.
199
200=item 4. A "Unicode String" is simply a string where each character can be
201validly interpreted as a Unicode code point.
202
203If you have UTF-8 encoded data, it is no longer a Unicode string, but a
204Unicode string encoded in UTF-8, giving you a binary string.
205
206=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
207
208It's a fact. Learn to live with it.
209
210=back
211
212I hope this helps :)
213
214
141=head1 OBJECT-ORIENTED INTERFACE 215=head1 OBJECT-ORIENTED INTERFACE
142 216
143The object oriented interface lets you configure your own encoding or 217The object oriented interface lets you configure your own encoding or
144decoding style, within the limits of supported formats. 218decoding style, within the limits of supported formats.
145 219
156 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) 230 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
157 => {"a": [1, 2]} 231 => {"a": [1, 2]}
158 232
159=item $json = $json->ascii ([$enable]) 233=item $json = $json->ascii ([$enable])
160 234
235=item $enabled = $json->get_ascii
236
161If C<$enable> is true (or missing), then the C<encode> method will not 237If C<$enable> is true (or missing), then the C<encode> method will not
162generate characters outside the code range C<0..127> (which is ASCII). Any 238generate characters outside the code range C<0..127> (which is ASCII). Any
163unicode characters outside that range will be escaped using either a 239Unicode characters outside that range will be escaped using either a
164single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, 240single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
165as per RFC4627. The resulting encoded JSON text can be treated as a native 241as per RFC4627. The resulting encoded JSON text can be treated as a native
166unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string, 242Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
167or any other superset of ASCII. 243or any other superset of ASCII.
168 244
169If C<$enable> is false, then the C<encode> method will not escape Unicode 245If 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 246characters unless required by the JSON syntax or other flags. This results
171in a faster and more compact format. 247in a faster and more compact format.
172 248
249See also the section I<ENCODING/CODESET FLAG NOTES> later in this
250document.
251
173The main use for this flag is to produce JSON texts that can be 252The 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 253transmitted over a 7-bit channel, as the encoded JSON texts will not
175contain any 8 bit characters. 254contain any 8 bit characters.
176 255
177 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 256 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
178 => ["\ud801\udc01"] 257 => ["\ud801\udc01"]
179 258
180=item $json = $json->latin1 ([$enable]) 259=item $json = $json->latin1 ([$enable])
181 260
261=item $enabled = $json->get_latin1
262
182If C<$enable> is true (or missing), then the C<encode> method will encode 263If C<$enable> is true (or missing), then the C<encode> method will encode
183the resulting JSON text as latin1 (or iso-8859-1), escaping any characters 264the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
184outside the code range C<0..255>. The resulting string can be treated as a 265outside the code range C<0..255>. The resulting string can be treated as a
185latin1-encoded JSON text or a native unicode string. The C<decode> method 266latin1-encoded JSON text or a native Unicode string. The C<decode> method
186will not be affected in any way by this flag, as C<decode> by default 267will not be affected in any way by this flag, as C<decode> by default
187expects unicode, which is a strict superset of latin1. 268expects Unicode, which is a strict superset of latin1.
188 269
189If C<$enable> is false, then the C<encode> method will not escape Unicode 270If C<$enable> is false, then the C<encode> method will not escape Unicode
190characters unless required by the JSON syntax or other flags. 271characters unless required by the JSON syntax or other flags.
272
273See also the section I<ENCODING/CODESET FLAG NOTES> later in this
274document.
191 275
192The main use for this flag is efficiently encoding binary data as JSON 276The 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 277text, as most octets will not be escaped, resulting in a smaller encoded
194size. The disadvantage is that the resulting JSON text is encoded 278size. The disadvantage is that the resulting JSON text is encoded
195in latin1 (and must correctly be treated as such when storing and 279in latin1 (and must correctly be treated as such when storing and
196transfering), a rare encoding for JSON. It is therefore most useful when 280transferring), a rare encoding for JSON. It is therefore most useful when
197you want to store data structures known to contain binary data efficiently 281you want to store data structures known to contain binary data efficiently
198in files or databases, not when talking to other JSON encoders/decoders. 282in files or databases, not when talking to other JSON encoders/decoders.
199 283
200 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] 284 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
201 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) 285 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
202 286
203=item $json = $json->utf8 ([$enable]) 287=item $json = $json->utf8 ([$enable])
288
289=item $enabled = $json->get_utf8
204 290
205If C<$enable> is true (or missing), then the C<encode> method will encode 291If C<$enable> is true (or missing), then the C<encode> method will encode
206the JSON result into UTF-8, as required by many protocols, while the 292the JSON result into UTF-8, as required by many protocols, while the
207C<decode> method expects to be handled an UTF-8-encoded string. Please 293C<decode> method expects to be handled an UTF-8-encoded string. Please
208note that UTF-8-encoded strings do not contain any characters outside the 294note that UTF-8-encoded strings do not contain any characters outside the
209range C<0..255>, they are thus useful for bytewise/binary I/O. In future 295range C<0..255>, they are thus useful for bytewise/binary I/O. In future
210versions, enabling this option might enable autodetection of the UTF-16 296versions, enabling this option might enable autodetection of the UTF-16
211and UTF-32 encoding families, as described in RFC4627. 297and UTF-32 encoding families, as described in RFC4627.
212 298
213If C<$enable> is false, then the C<encode> method will return the JSON 299If 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 300string 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 301Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
216to be done yourself, e.g. using the Encode module. 302to be done yourself, e.g. using the Encode module.
303
304See also the section I<ENCODING/CODESET FLAG NOTES> later in this
305document.
217 306
218Example, output UTF-16BE-encoded JSON: 307Example, output UTF-16BE-encoded JSON:
219 308
220 use Encode; 309 use Encode;
221 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); 310 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
242 ] 331 ]
243 } 332 }
244 333
245=item $json = $json->indent ([$enable]) 334=item $json = $json->indent ([$enable])
246 335
336=item $enabled = $json->get_indent
337
247If C<$enable> is true (or missing), then the C<encode> method will use a multiline 338If C<$enable> is true (or missing), then the C<encode> method will use a multiline
248format as output, putting every array member or object/hash key-value pair 339format as output, putting every array member or object/hash key-value pair
249into its own line, identing them properly. 340into its own line, indenting them properly.
250 341
251If C<$enable> is false, no newlines or indenting will be produced, and the 342If C<$enable> is false, no newlines or indenting will be produced, and the
252resulting JSON text is guarenteed not to contain any C<newlines>. 343resulting JSON text is guaranteed not to contain any C<newlines>.
253 344
254This setting has no effect when decoding JSON texts. 345This setting has no effect when decoding JSON texts.
255 346
256=item $json = $json->space_before ([$enable]) 347=item $json = $json->space_before ([$enable])
348
349=item $enabled = $json->get_space_before
257 350
258If C<$enable> is true (or missing), then the C<encode> method will add an extra 351If C<$enable> is true (or missing), then the C<encode> method will add an extra
259optional space before the C<:> separating keys from values in JSON objects. 352optional space before the C<:> separating keys from values in JSON objects.
260 353
261If C<$enable> is false, then the C<encode> method will not add any extra 354If C<$enable> is false, then the C<encode> method will not add any extra
267Example, space_before enabled, space_after and indent disabled: 360Example, space_before enabled, space_after and indent disabled:
268 361
269 {"key" :"value"} 362 {"key" :"value"}
270 363
271=item $json = $json->space_after ([$enable]) 364=item $json = $json->space_after ([$enable])
365
366=item $enabled = $json->get_space_after
272 367
273If C<$enable> is true (or missing), then the C<encode> method will add an extra 368If 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 369optional space after the C<:> separating keys from values in JSON objects
275and extra whitespace after the C<,> separating key-value pairs and array 370and extra whitespace after the C<,> separating key-value pairs and array
276members. 371members.
282 377
283Example, space_before and indent disabled, space_after enabled: 378Example, space_before and indent disabled, space_after enabled:
284 379
285 {"key": "value"} 380 {"key": "value"}
286 381
382=item $json = $json->relaxed ([$enable])
383
384=item $enabled = $json->get_relaxed
385
386If C<$enable> is true (or missing), then C<decode> will accept some
387extensions to normal JSON syntax (see below). C<encode> will not be
388affected in anyway. I<Be aware that this option makes you accept invalid
389JSON texts as if they were valid!>. I suggest only to use this option to
390parse application-specific files written by humans (configuration files,
391resource files etc.)
392
393If C<$enable> is false (the default), then C<decode> will only accept
394valid JSON texts.
395
396Currently accepted extensions are:
397
398=over 4
399
400=item * list items can have an end-comma
401
402JSON I<separates> array elements and key-value pairs with commas. This
403can be annoying if you write JSON texts manually and want to be able to
404quickly append elements, so this extension accepts comma at the end of
405such items not just between them:
406
407 [
408 1,
409 2, <- this comma not normally allowed
410 ]
411 {
412 "k1": "v1",
413 "k2": "v2", <- this comma not normally allowed
414 }
415
416=item * shell-style '#'-comments
417
418Whenever JSON allows whitespace, shell-style comments are additionally
419allowed. They are terminated by the first carriage-return or line-feed
420character, after which more white-space and comments are allowed.
421
422 [
423 1, # this comment not allowed in JSON
424 # neither this one...
425 ]
426
427=back
428
287=item $json = $json->canonical ([$enable]) 429=item $json = $json->canonical ([$enable])
430
431=item $enabled = $json->get_canonical
288 432
289If C<$enable> is true (or missing), then the C<encode> method will output JSON objects 433If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
290by sorting their keys. This is adding a comparatively high overhead. 434by sorting their keys. This is adding a comparatively high overhead.
291 435
292If C<$enable> is false, then the C<encode> method will output key-value 436If 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 437pairs in the order Perl stores them (which will likely change between runs
294of the same script). 438of the same script).
295 439
296This option is useful if you want the same data structure to be encoded as 440This 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, 441the 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, 442the same hash might be encoded differently even if contains the same data,
299as key-value pairs have no inherent ordering in Perl. 443as key-value pairs have no inherent ordering in Perl.
300 444
301This setting has no effect when decoding JSON texts. 445This setting has no effect when decoding JSON texts.
302 446
303=item $json = $json->allow_nonref ([$enable]) 447=item $json = $json->allow_nonref ([$enable])
448
449=item $enabled = $json->get_allow_nonref
304 450
305If C<$enable> is true (or missing), then the C<encode> method can convert a 451If 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, 452non-reference into its corresponding string, number or null JSON value,
307which is an extension to RFC4627. Likewise, C<decode> will accept those JSON 453which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
308values instead of croaking. 454values instead of croaking.
316resulting in an invalid JSON text: 462resulting in an invalid JSON text:
317 463
318 JSON::XS->new->allow_nonref->encode ("Hello, World!") 464 JSON::XS->new->allow_nonref->encode ("Hello, World!")
319 => "Hello, World!" 465 => "Hello, World!"
320 466
467=item $json = $json->allow_unknown ([$enable])
468
469=item $enabled = $json->get_allow_unknown
470
471If C<$enable> is true (or missing), then C<encode> will I<not> throw an
472exception when it encounters values it cannot represent in JSON (for
473example, filehandles) but instead will encode a JSON C<null> value. Note
474that blessed objects are not included here and are handled separately by
475c<allow_nonref>.
476
477If C<$enable> is false (the default), then C<encode> will throw an
478exception when it encounters anything it cannot encode as JSON.
479
480This option does not affect C<decode> in any way, and it is recommended to
481leave it off unless you know your communications partner.
482
321=item $json = $json->allow_blessed ([$enable]) 483=item $json = $json->allow_blessed ([$enable])
484
485=item $enabled = $json->get_allow_blessed
322 486
323If C<$enable> is true (or missing), then the C<encode> method will not 487If C<$enable> is true (or missing), then the C<encode> method will not
324barf when it encounters a blessed reference. Instead, the value of the 488barf when it encounters a blessed reference. Instead, the value of the
325B<convert_blessed> option will decide wether C<null> (C<convert_blessed> 489B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
326disabled or no C<to_json> method found) or a representation of the 490disabled or no C<TO_JSON> method found) or a representation of the
327object (C<convert_blessed> enabled and C<to_json> method found) is being 491object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
328encoded. Has no effect on C<decode>. 492encoded. Has no effect on C<decode>.
329 493
330If C<$enable> is false (the default), then C<encode> will throw an 494If C<$enable> is false (the default), then C<encode> will throw an
331exception when it encounters a blessed object. 495exception when it encounters a blessed object.
332 496
333=item $json = $json->convert_blessed ([$enable]) 497=item $json = $json->convert_blessed ([$enable])
498
499=item $enabled = $json->get_convert_blessed
334 500
335If C<$enable> is true (or missing), then C<encode>, upon encountering a 501If C<$enable> is true (or missing), then C<encode>, upon encountering a
336blessed object, will check for the availability of the C<TO_JSON> method 502blessed object, will check for the availability of the C<TO_JSON> method
337on the object's class. If found, it will be called in scalar context 503on the object's class. If found, it will be called in scalar context
338and the resulting scalar will be encoded instead of the object. If no 504and the resulting scalar will be encoded instead of the object. If no
342The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON> 508The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
343returns other blessed objects, those will be handled in the same 509returns other blessed objects, those will be handled in the same
344way. C<TO_JSON> must take care of not causing an endless recursion cycle 510way. C<TO_JSON> must take care of not causing an endless recursion cycle
345(== crash) in this case. The name of C<TO_JSON> was chosen because other 511(== crash) in this case. The name of C<TO_JSON> was chosen because other
346methods called by the Perl core (== not by the user of the object) are 512methods called by the Perl core (== not by the user of the object) are
347usually in upper case letters and to avoid collisions with the C<to_json> 513usually in upper case letters and to avoid collisions with any C<to_json>
348function. 514function or method.
349 515
350This setting does not yet influence C<decode> in any way, but in the 516This setting does not yet influence C<decode> in any way, but in the
351future, global hooks might get installed that influence C<decode> and are 517future, global hooks might get installed that influence C<decode> and are
352enabled by this setting. 518enabled by this setting.
353 519
354If C<$enable> is false, then the C<allow_blessed> setting will decide what 520If C<$enable> is false, then the C<allow_blessed> setting will decide what
355to do when a blessed object is found. 521to do when a blessed object is found.
356 522
523=item $json = $json->filter_json_object ([$coderef->($hashref)])
524
525When C<$coderef> is specified, it will be called from C<decode> each
526time it decodes a JSON object. The only argument is a reference to the
527newly-created hash. If the code references returns a single scalar (which
528need not be a reference), this value (i.e. a copy of that scalar to avoid
529aliasing) is inserted into the deserialised data structure. If it returns
530an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
531original deserialised hash will be inserted. This setting can slow down
532decoding considerably.
533
534When C<$coderef> is omitted or undefined, any existing callback will
535be removed and C<decode> will not change the deserialised hash in any
536way.
537
538Example, convert all JSON objects into the integer 5:
539
540 my $js = JSON::XS->new->filter_json_object (sub { 5 });
541 # returns [5]
542 $js->decode ('[{}]')
543 # throw an exception because allow_nonref is not enabled
544 # so a lone 5 is not allowed.
545 $js->decode ('{"a":1, "b":2}');
546
547=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
548
549Works remotely similar to C<filter_json_object>, but is only called for
550JSON objects having a single key named C<$key>.
551
552This C<$coderef> is called before the one specified via
553C<filter_json_object>, if any. It gets passed the single value in the JSON
554object. If it returns a single value, it will be inserted into the data
555structure. If it returns nothing (not even C<undef> but the empty list),
556the callback from C<filter_json_object> will be called next, as if no
557single-key callback were specified.
558
559If C<$coderef> is omitted or undefined, the corresponding callback will be
560disabled. There can only ever be one callback for a given key.
561
562As this callback gets called less often then the C<filter_json_object>
563one, decoding speed will not usually suffer as much. Therefore, single-key
564objects make excellent targets to serialise Perl objects into, especially
565as single-key JSON objects are as close to the type-tagged value concept
566as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
567support this in any way, so you need to make sure your data never looks
568like a serialised Perl hash.
569
570Typical names for the single object key are C<__class_whatever__>, or
571C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
572things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
573with real hashes.
574
575Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
576into the corresponding C<< $WIDGET{<id>} >> object:
577
578 # return whatever is in $WIDGET{5}:
579 JSON::XS
580 ->new
581 ->filter_json_single_key_object (__widget__ => sub {
582 $WIDGET{ $_[0] }
583 })
584 ->decode ('{"__widget__": 5')
585
586 # this can be used with a TO_JSON method in some "widget" class
587 # for serialisation to json:
588 sub WidgetBase::TO_JSON {
589 my ($self) = @_;
590
591 unless ($self->{id}) {
592 $self->{id} = ..get..some..id..;
593 $WIDGET{$self->{id}} = $self;
594 }
595
596 { __widget__ => $self->{id} }
597 }
598
357=item $json = $json->shrink ([$enable]) 599=item $json = $json->shrink ([$enable])
600
601=item $enabled = $json->get_shrink
358 602
359Perl usually over-allocates memory a bit when allocating space for 603Perl usually over-allocates memory a bit when allocating space for
360strings. This flag optionally resizes strings generated by either 604strings. This flag optionally resizes strings generated by either
361C<encode> or C<decode> to their minimum size possible. This can save 605C<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 606memory when your JSON texts are either very very long or you have many
380strings that look like integers or floats into integers or floats 624strings that look like integers or floats into integers or floats
381internally (there is no difference on the Perl level), saving space. 625internally (there is no difference on the Perl level), saving space.
382 626
383=item $json = $json->max_depth ([$maximum_nesting_depth]) 627=item $json = $json->max_depth ([$maximum_nesting_depth])
384 628
629=item $max_depth = $json->get_max_depth
630
385Sets the maximum nesting level (default C<512>) accepted while encoding 631Sets the maximum nesting level (default C<512>) accepted while encoding
386or decoding. If the JSON text or Perl data structure has an equal or 632or 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 633data structure, then the encoder and decoder will stop and croak at that
388stop and croak at that point. 634point.
389 635
390Nesting level is defined by number of hash- or arrayrefs that the encoder 636Nesting 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<[> 637needs to traverse to reach a given point or the number of C<{> or C<[>
392characters without their matching closing parenthesis crossed to reach a 638characters without their matching closing parenthesis crossed to reach a
393given character in a string. 639given character in a string.
394 640
395Setting the maximum depth to one disallows any nesting, so that ensures 641Setting the maximum depth to one disallows any nesting, so that ensures
396that the object is only a single hash/object or array. 642that the object is only a single hash/object or array.
397 643
398The argument to C<max_depth> will be rounded up to the next highest power
399of two. If no argument is given, the highest possible setting will be 644If no argument is given, the highest possible setting will be used, which
400used, which is rarely useful. 645is rarely useful.
646
647Note that nesting is implemented by recursion in C. The default value has
648been chosen to be as large as typical operating systems allow without
649crashing.
401 650
402See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 651See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
403 652
404=item $json = $json->max_size ([$maximum_string_size]) 653=item $json = $json->max_size ([$maximum_string_size])
654
655=item $max_size = $json->get_max_size
405 656
406Set the maximum length a JSON text may have (in bytes) where decoding is 657Set 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> 658being 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 659is called on a string that is longer then this many bytes, it will not
409attempt to decode the string but throw an exception. This setting has no 660attempt to decode the string but throw an exception. This setting has no
410effect on C<encode> (yet). 661effect on C<encode> (yet).
411 662
412The argument to C<max_size> will be rounded up to the next B<highest> 663If no argument is given, the limit check will be deactivated (same as when
413power of two (so may be more than requested). If no argument is given, the 664C<0> is specified).
414limit check will be deactivated (same as when C<0> is specified).
415 665
416See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 666See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
417 667
418=item $json_text = $json->encode ($perl_scalar) 668=item $json_text = $json->encode ($perl_scalar)
419 669
448 => ([], 3) 698 => ([], 3)
449 699
450=back 700=back
451 701
452 702
703=head1 INCREMENTAL PARSING
704
705In some cases, there is the need for incremental parsing of JSON
706texts. While this module always has to keep both JSON text and resulting
707Perl data structure in memory at one time, it does allow you to parse a
708JSON stream incrementally. It does so by accumulating text until it has
709a full JSON object, which it then can decode. This process is similar to
710using C<decode_prefix> to see if a full JSON object is available, but
711is much more efficient (and can be implemented with a minimum of method
712calls).
713
714JSON::XS will only attempt to parse the JSON text once it is sure it
715has enough text to get a decisive result, using a very simple but
716truly incremental parser. This means that it sometimes won't stop as
717early as the full parser, for example, it doesn't detect parenthese
718mismatches. The only thing it guarantees is that it starts decoding as
719soon as a syntactically valid JSON text has been seen. This means you need
720to set resource limits (e.g. C<max_size>) to ensure the parser will stop
721parsing in the presence if syntax errors.
722
723The following methods implement this incremental parser.
724
725=over 4
726
727=item [void, scalar or list context] = $json->incr_parse ([$string])
728
729This is the central parsing function. It can both append new text and
730extract objects from the stream accumulated so far (both of these
731functions are optional).
732
733If C<$string> is given, then this string is appended to the already
734existing JSON fragment stored in the C<$json> object.
735
736After that, if the function is called in void context, it will simply
737return without doing anything further. This can be used to add more text
738in as many chunks as you want.
739
740If the method is called in scalar context, then it will try to extract
741exactly I<one> JSON object. If that is successful, it will return this
742object, otherwise it will return C<undef>. If there is a parse error,
743this method will croak just as C<decode> would do (one can then use
744C<incr_skip> to skip the errornous part). This is the most common way of
745using the method.
746
747And finally, in list context, it will try to extract as many objects
748from the stream as it can find and return them, or the empty list
749otherwise. For this to work, there must be no separators between the JSON
750objects or arrays, instead they must be concatenated back-to-back. If
751an error occurs, an exception will be raised as in the scalar context
752case. Note that in this case, any previously-parsed JSON texts will be
753lost.
754
755=item $lvalue_string = $json->incr_text
756
757This method returns the currently stored JSON fragment as an lvalue, that
758is, you can manipulate it. This I<only> works when a preceding call to
759C<incr_parse> in I<scalar context> successfully returned an object. Under
760all other circumstances you must not call this function (I mean it.
761although in simple tests it might actually work, it I<will> fail under
762real world conditions). As a special exception, you can also call this
763method before having parsed anything.
764
765This function is useful in two cases: a) finding the trailing text after a
766JSON object or b) parsing multiple JSON objects separated by non-JSON text
767(such as commas).
768
769=item $json->incr_skip
770
771This will reset the state of the incremental parser and will remove the
772parsed text from the input buffer. This is useful after C<incr_parse>
773died, in which case the input buffer and incremental parser state is left
774unchanged, to skip the text parsed so far and to reset the parse state.
775
776=item $json->incr_reset
777
778This completely resets the incremental parser, that is, after this call,
779it will be as if the parser had never parsed anything.
780
781This is useful if you want ot repeatedly parse JSON objects and want to
782ignore any trailing data, which means you have to reset the parser after
783each successful decode.
784
785=back
786
787=head2 LIMITATIONS
788
789All options that affect decoding are supported, except
790C<allow_nonref>. The reason for this is that it cannot be made to
791work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
792them back to back and still decode them perfectly. This does not hold true
793for JSON numbers, however.
794
795For example, is the string C<1> a single JSON number, or is it simply the
796start of C<12>? Or is C<12> a single JSON number, or the concatenation
797of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
798takes the conservative route and disallows this case.
799
800=head2 EXAMPLES
801
802Some examples will make all this clearer. First, a simple example that
803works similarly to C<decode_prefix>: We want to decode the JSON object at
804the start of a string and identify the portion after the JSON object:
805
806 my $text = "[1,2,3] hello";
807
808 my $json = new JSON::XS;
809
810 my $obj = $json->incr_parse ($text)
811 or die "expected JSON object or array at beginning of string";
812
813 my $tail = $json->incr_text;
814 # $tail now contains " hello"
815
816Easy, isn't it?
817
818Now for a more complicated example: Imagine a hypothetical protocol where
819you read some requests from a TCP stream, and each request is a JSON
820array, without any separation between them (in fact, it is often useful to
821use newlines as "separators", as these get interpreted as whitespace at
822the start of the JSON text, which makes it possible to test said protocol
823with C<telnet>...).
824
825Here is how you'd do it (it is trivial to write this in an event-based
826manner):
827
828 my $json = new JSON::XS;
829
830 # read some data from the socket
831 while (sysread $socket, my $buf, 4096) {
832
833 # split and decode as many requests as possible
834 for my $request ($json->incr_parse ($buf)) {
835 # act on the $request
836 }
837 }
838
839Another complicated example: Assume you have a string with JSON objects
840or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
841[3]>). To parse them, we have to skip the commas between the JSON texts,
842and here is where the lvalue-ness of C<incr_text> comes in useful:
843
844 my $text = "[1],[2], [3]";
845 my $json = new JSON::XS;
846
847 # void context, so no parsing done
848 $json->incr_parse ($text);
849
850 # now extract as many objects as possible. note the
851 # use of scalar context so incr_text can be called.
852 while (my $obj = $json->incr_parse) {
853 # do something with $obj
854
855 # now skip the optional comma
856 $json->incr_text =~ s/^ \s* , //x;
857 }
858
859Now lets go for a very complex example: Assume that you have a gigantic
860JSON array-of-objects, many gigabytes in size, and you want to parse it,
861but you cannot load it into memory fully (this has actually happened in
862the real world :).
863
864Well, you lost, you have to implement your own JSON parser. But JSON::XS
865can still help you: You implement a (very simple) array parser and let
866JSON decode the array elements, which are all full JSON objects on their
867own (this wouldn't work if the array elements could be JSON numbers, for
868example):
869
870 my $json = new JSON::XS;
871
872 # open the monster
873 open my $fh, "<bigfile.json"
874 or die "bigfile: $!";
875
876 # first parse the initial "["
877 for (;;) {
878 sysread $fh, my $buf, 65536
879 or die "read error: $!";
880 $json->incr_parse ($buf); # void context, so no parsing
881
882 # Exit the loop once we found and removed(!) the initial "[".
883 # In essence, we are (ab-)using the $json object as a simple scalar
884 # we append data to.
885 last if $json->incr_text =~ s/^ \s* \[ //x;
886 }
887
888 # now we have the skipped the initial "[", so continue
889 # parsing all the elements.
890 for (;;) {
891 # in this loop we read data until we got a single JSON object
892 for (;;) {
893 if (my $obj = $json->incr_parse) {
894 # do something with $obj
895 last;
896 }
897
898 # add more data
899 sysread $fh, my $buf, 65536
900 or die "read error: $!";
901 $json->incr_parse ($buf); # void context, so no parsing
902 }
903
904 # in this loop we read data until we either found and parsed the
905 # separating "," between elements, or the final "]"
906 for (;;) {
907 # first skip whitespace
908 $json->incr_text =~ s/^\s*//;
909
910 # if we find "]", we are done
911 if ($json->incr_text =~ s/^\]//) {
912 print "finished.\n";
913 exit;
914 }
915
916 # if we find ",", we can continue with the next element
917 if ($json->incr_text =~ s/^,//) {
918 last;
919 }
920
921 # if we find anything else, we have a parse error!
922 if (length $json->incr_text) {
923 die "parse error near ", $json->incr_text;
924 }
925
926 # else add more data
927 sysread $fh, my $buf, 65536
928 or die "read error: $!";
929 $json->incr_parse ($buf); # void context, so no parsing
930 }
931
932This is a complex example, but most of the complexity comes from the fact
933that we are trying to be correct (bear with me if I am wrong, I never ran
934the above example :).
935
936
937
453=head1 MAPPING 938=head1 MAPPING
454 939
455This section describes how JSON::XS maps Perl values to JSON values and 940This 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 941vice versa. These mappings are designed to "do the right thing" in most
457circumstances automatically, preserving round-tripping characteristics 942circumstances automatically, preserving round-tripping characteristics
458(what you put in comes out as something equivalent). 943(what you put in comes out as something equivalent).
459 944
460For the more enlightened: note that in the following descriptions, 945For the more enlightened: note that in the following descriptions,
461lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl> 946lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
462refers to the abstract Perl language itself. 947refers to the abstract Perl language itself.
463 948
464 949
465=head2 JSON -> PERL 950=head2 JSON -> PERL
466 951
467=over 4 952=over 4
468 953
469=item object 954=item object
470 955
471A JSON object becomes a reference to a hash in Perl. No ordering of object 956A 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). 957keys is preserved (JSON does not preserve object key ordering itself).
473 958
474=item array 959=item array
475 960
476A JSON array becomes a reference to an array in Perl. 961A JSON array becomes a reference to an array in Perl.
477 962
481are represented by the same codepoints in the Perl string, so no manual 966are represented by the same codepoints in the Perl string, so no manual
482decoding is necessary. 967decoding is necessary.
483 968
484=item number 969=item number
485 970
486A JSON number becomes either an integer or numeric (floating point) 971A JSON number becomes either an integer, numeric (floating point) or
487scalar in perl, depending on its range and any fractional parts. On the 972string 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 973the Perl level, there is no difference between those as Perl handles all
489conversion details, but an integer may take slightly less memory and might 974the conversion details, but an integer may take slightly less memory and
490represent more values exactly than (floating point) numbers. 975might represent more values exactly than floating point numbers.
976
977If the number consists of digits only, JSON::XS will try to represent
978it as an integer value. If that fails, it will try to represent it as
979a numeric (floating point) value if that is possible without loss of
980precision. Otherwise it will preserve the number as a string value (in
981which case you lose roundtripping ability, as the JSON number will be
982re-encoded toa JSON string).
983
984Numbers containing a fractional or exponential part will always be
985represented as numeric (floating point) values, possibly at a loss of
986precision (in which case you might lose perfect roundtripping ability, but
987the JSON number will still be re-encoded as a JSON number).
491 988
492=item true, false 989=item true, false
493 990
494These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, 991These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
495respectively. They are overloaded to act almost exactly like the numbers 992respectively. 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 993C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
497the C<JSON::XS::is_bool> function. 994the C<JSON::XS::is_bool> function.
498 995
499=item null 996=item null
500 997
501A JSON null atom becomes C<undef> in Perl. 998A JSON null atom becomes C<undef> in Perl.
532Other unblessed references are generally not allowed and will cause an 1029Other unblessed references are generally not allowed and will cause an
533exception to be thrown, except for references to the integers C<0> and 1030exception 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 1031C<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. 1032also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
536 1033
537 to_json [\0,JSON::XS::true] # yields [false,true] 1034 encode_json [\0, JSON::XS::true] # yields [false,true]
538 1035
539=item JSON::XS::true, JSON::XS::false 1036=item JSON::XS::true, JSON::XS::false
540 1037
541These special values become JSON true and JSON false values, 1038These special values become JSON true and JSON false values,
542respectively. You cna alos use C<\1> and C<\0> directly if you want. 1039respectively. You can also use C<\1> and C<\0> directly if you want.
543 1040
544=item blessed objects 1041=item blessed objects
545 1042
546Blessed objects are not allowed. JSON::XS currently tries to encode their 1043Blessed objects are not directly representable in JSON. See the
547underlying representation (hash- or arrayref), but this behaviour might 1044C<allow_blessed> and C<convert_blessed> methods on various options on
548change in future versions. 1045how to deal with this: basically, you can choose between throwing an
1046exception, encoding the reference as if it weren't blessed, or provide
1047your own serialiser method.
549 1048
550=item simple scalars 1049=item simple scalars
551 1050
552Simple Perl scalars (any scalar that is not a reference) are the most 1051Simple Perl scalars (any scalar that is not a reference) are the most
553difficult objects to encode: JSON::XS will encode undefined scalars as 1052difficult objects to encode: JSON::XS will encode undefined scalars as
554JSON null value, scalars that have last been used in a string context 1053JSON C<null> values, scalars that have last been used in a string context
555before encoding as JSON strings and anything else as number value: 1054before encoding as JSON strings, and anything else as number value:
556 1055
557 # dump as number 1056 # dump as number
558 to_json [2] # yields [2] 1057 encode_json [2] # yields [2]
559 to_json [-3.0e17] # yields [-3e+17] 1058 encode_json [-3.0e17] # yields [-3e+17]
560 my $value = 5; to_json [$value] # yields [5] 1059 my $value = 5; encode_json [$value] # yields [5]
561 1060
562 # used as string, so dump as string 1061 # used as string, so dump as string
563 print $value; 1062 print $value;
564 to_json [$value] # yields ["5"] 1063 encode_json [$value] # yields ["5"]
565 1064
566 # undef becomes null 1065 # undef becomes null
567 to_json [undef] # yields [null] 1066 encode_json [undef] # yields [null]
568 1067
569You can force the type to be a string by stringifying it: 1068You can force the type to be a JSON string by stringifying it:
570 1069
571 my $x = 3.1; # some variable containing a number 1070 my $x = 3.1; # some variable containing a number
572 "$x"; # stringified 1071 "$x"; # stringified
573 $x .= ""; # another, more awkward way to stringify 1072 $x .= ""; # another, more awkward way to stringify
574 print $x; # perl does it for you, too, quite often 1073 print $x; # perl does it for you, too, quite often
575 1074
576You can force the type to be a number by numifying it: 1075You can force the type to be a JSON number by numifying it:
577 1076
578 my $x = "3"; # some variable containing a string 1077 my $x = "3"; # some variable containing a string
579 $x += 0; # numify it, ensuring it will be dumped as a number 1078 $x += 0; # numify it, ensuring it will be dumped as a number
580 $x *= 1; # same thing, the choise is yours. 1079 $x *= 1; # same thing, the choice is yours.
581 1080
582You can not currently output JSON booleans or force the type in other, 1081You can not currently force the type in other, less obscure, ways. Tell me
583less obscure, ways. Tell me if you need this capability. 1082if you need this capability (but don't forget to explain why it's needed
1083:).
584 1084
585=back 1085=back
586 1086
587 1087
588=head1 COMPARISON 1088=head1 ENCODING/CODESET FLAG NOTES
589 1089
590As already mentioned, this module was created because none of the existing 1090The interested reader might have seen a number of flags that signify
591JSON modules could be made to work correctly. First I will describe the 1091encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
592problems (or pleasures) I encountered with various existing JSON modules, 1092some confusion on what these do, so here is a short comparison:
593followed by some benchmark values. JSON::XS was designed not to suffer 1093
594from any of these problems or limitations. 1094C<utf8> controls whether the JSON text created by C<encode> (and expected
1095by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
1096control whether C<encode> escapes character values outside their respective
1097codeset range. Neither of these flags conflict with each other, although
1098some combinations make less sense than others.
1099
1100Care has been taken to make all flags symmetrical with respect to
1101C<encode> and C<decode>, that is, texts encoded with any combination of
1102these flag values will be correctly decoded when the same flags are used
1103- in general, if you use different flag settings while encoding vs. when
1104decoding you likely have a bug somewhere.
1105
1106Below comes a verbose discussion of these flags. Note that a "codeset" is
1107simply an abstract set of character-codepoint pairs, while an encoding
1108takes those codepoint numbers and I<encodes> them, in our case into
1109octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
1110and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
1111the same time, which can be confusing.
595 1112
596=over 4 1113=over 4
597 1114
598=item JSON 1.07 1115=item C<utf8> flag disabled
599 1116
600Slow (but very portable, as it is written in pure Perl). 1117When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
1118and expect Unicode strings, that is, characters with high ordinal Unicode
1119values (> 255) will be encoded as such characters, and likewise such
1120characters are decoded as-is, no canges to them will be done, except
1121"(re-)interpreting" them as Unicode codepoints or Unicode characters,
1122respectively (to Perl, these are the same thing in strings unless you do
1123funny/weird/dumb stuff).
601 1124
602Undocumented/buggy Unicode handling (how JSON handles unicode values is 1125This is useful when you want to do the encoding yourself (e.g. when you
603undocumented. One can get far by feeding it unicode strings and doing 1126want to have UTF-16 encoded JSON texts) or when some other layer does
604en-/decoding oneself, but unicode escapes are not working properly). 1127the encoding for you (for example, when printing to a terminal using a
1128filehandle that transparently encodes to UTF-8 you certainly do NOT want
1129to UTF-8 encode your data first and have Perl encode it another time).
605 1130
606No roundtripping (strings get clobbered if they look like numbers, e.g. 1131=item C<utf8> flag enabled
607the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
608decode into the number 2.
609 1132
610=item JSON::PC 0.01 1133If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
1134characters using the corresponding UTF-8 multi-byte sequence, and will
1135expect your input strings to be encoded as UTF-8, that is, no "character"
1136of the input string must have any value > 255, as UTF-8 does not allow
1137that.
611 1138
612Very fast. 1139The C<utf8> flag therefore switches between two modes: disabled means you
1140will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
1141octet/binary string in Perl.
613 1142
614Undocumented/buggy Unicode handling. 1143=item C<latin1> or C<ascii> flags enabled
615 1144
616No roundtripping. 1145With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
1146with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
1147characters as specified by the C<utf8> flag.
617 1148
618Has problems handling many Perl values (e.g. regex results and other magic 1149If C<utf8> is disabled, then the result is also correctly encoded in those
619values will make it croak). 1150character sets (as both are proper subsets of Unicode, meaning that a
1151Unicode string with all character values < 256 is the same thing as a
1152ISO-8859-1 string, and a Unicode string with all character values < 128 is
1153the same thing as an ASCII string in Perl).
620 1154
621Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> 1155If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
622which is not a valid JSON text. 1156regardless of these flags, just some more characters will be escaped using
1157C<\uXXXX> then before.
623 1158
624Unmaintained (maintainer unresponsive for many months, bugs are not 1159Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
625getting fixed). 1160encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
1161encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
1162a subset of Unicode), while ASCII is.
626 1163
627=item JSON::Syck 0.21 1164Surprisingly, C<decode> will ignore these flags and so treat all input
1165values as governed by the C<utf8> flag. If it is disabled, this allows you
1166to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
1167Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
628 1168
629Very buggy (often crashes). 1169So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
1170they only govern when the JSON output engine escapes a character or not.
630 1171
631Very inflexible (no human-readable format supported, format pretty much 1172The main use for C<latin1> is to relatively efficiently store binary data
632undocumented. I need at least a format for easy reading by humans and a 1173as JSON, at the expense of breaking compatibility with most JSON decoders.
633single-line compact format for use in a protocol, and preferably a way to
634generate ASCII-only JSON texts).
635 1174
636Completely broken (and confusingly documented) Unicode handling (unicode 1175The main use for C<ascii> is to force the output to not contain characters
637escapes are not working properly, you need to set ImplicitUnicode to 1176with values > 127, which means you can interpret the resulting string
638I<different> values on en- and decoding to get symmetric behaviour). 1177as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
639 11788-bit-encoding, and still get the same data structure back. This is useful
640No roundtripping (simple cases work, but this depends on wether the scalar 1179when your channel for JSON transfer is not 8-bit clean or the encoding
641value was used in a numeric context or not). 1180might be mangled in between (e.g. in mail), and works because ASCII is a
642 1181proper subset of most 8-bit and multibyte encodings in use in the world.
643Dumping hashes may skip hash values depending on iterator state.
644
645Unmaintained (maintainer unresponsive for many months, bugs are not
646getting fixed).
647
648Does not check input for validity (i.e. will accept non-JSON input and
649return "something" instead of raising an exception. This is a security
650issue: imagine two banks transfering money between each other using
651JSON. 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
653good protocol will at least recover, that is extra unnecessary work and
654the transaction will still not succeed).
655
656=item JSON::DWIW 0.04
657
658Very fast. Very natural. Very nice.
659
660Undocumented unicode handling (but the best of the pack. Unicode escapes
661still don't get parsed properly).
662
663Very inflexible.
664
665No roundtripping.
666
667Does not generate valid JSON texts (key strings are often unquoted, empty keys
668result in nothing being output)
669
670Does not check input for validity.
671 1182
672=back 1183=back
673 1184
674 1185
675=head2 JSON and YAML 1186=head2 JSON and YAML
676 1187
677You often hear that JSON is a subset (or a close subset) of YAML. This is, 1188You 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 1189hysteria(*) 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. 1190so let me state it clearly: I<in general, there is no way to configure
1191JSON::XS to output a data structure as valid YAML> that works in all
1192cases.
680 1193
681If you really must use JSON::XS to generate YAML, you should use this 1194If you really must use JSON::XS to generate YAML, you should use this
682algorithm (subject to change in future versions): 1195algorithm (subject to change in future versions):
683 1196
684 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1197 my $to_yaml = JSON::XS->new->utf8->space_after (1);
685 my $yaml = $to_yaml->encode ($ref) . "\n"; 1198 my $yaml = $to_yaml->encode ($ref) . "\n";
686 1199
687This will usually generate JSON texts that also parse as valid 1200This will I<usually> generate JSON texts that also parse as valid
688YAML. Please note that YAML has hardcoded limits on (simple) object key 1201YAML. 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 1202lengths that JSON doesn't have and also has different and incompatible
1203unicode handling, so you should make sure that your hash keys are
690keys are noticably shorter than the 1024 characters YAML allows. 1204noticeably shorter than the 1024 "stream characters" YAML allows and that
1205you do not have characters with codepoint values outside the Unicode BMP
1206(basic multilingual page). YAML also does not allow C<\/> sequences in
1207strings (which JSON::XS does not I<currently> generate, but other JSON
1208generators might).
691 1209
692There might be other incompatibilities that I am not aware of. In general 1210There might be other incompatibilities that I am not aware of (or the YAML
1211specification 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, 1212general 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 1213versa, or try to parse JSON with a YAML parser or vice versa: chances are
695that you will run into severe interoperability problems. 1214high that you will run into severe interoperability problems when you
1215least expect it.
1216
1217=over 4
1218
1219=item (*)
1220
1221I have been pressured multiple times by Brian Ingerson (one of the
1222authors of the YAML specification) to remove this paragraph, despite him
1223acknowledging that the actual incompatibilities exist. As I was personally
1224bitten by this "JSON is YAML" lie, I refused and said I will continue to
1225educate people about these issues, so others do not run into the same
1226problem again and again. After this, Brian called me a (quote)I<complete
1227and worthless idiot>(unquote).
1228
1229In my opinion, instead of pressuring and insulting people who actually
1230clarify issues with YAML and the wrong statements of some of its
1231proponents, I would kindly suggest reading the JSON spec (which is not
1232that difficult or long) and finally make YAML compatible to it, and
1233educating users about the changes, instead of spreading lies about the
1234real compatibility for many I<years> and trying to silence people who
1235point out that it isn't true.
1236
1237=back
696 1238
697 1239
698=head2 SPEED 1240=head2 SPEED
699 1241
700It seems that JSON::XS is surprisingly fast, as shown in the following 1242It 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 1243tables. 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 1244in the JSON::XS distribution, to make it easy to compare on your own
703system. 1245system.
704 1246
705First comes a comparison between various modules using a very short 1247First comes a comparison between various modules using
706single-line JSON string: 1248a very short single-line JSON string (also available at
1249L<http://dist.schmorp.de/misc/json/short.json>).
707 1250
708 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1251 {"method": "handleMessage", "params": ["user1",
709 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1252 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1253 true, false]}
710 1254
711It shows the number of encodes/decodes per second (JSON::XS uses 1255It shows the number of encodes/decodes per second (JSON::XS uses
712the functional interface, while JSON::XS/2 uses the OO interface 1256the functional interface, while JSON::XS/2 uses the OO interface
713with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables 1257with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
714shrink). Higher is better: 1258shrink). Higher is better:
715 1259
716 module | encode | decode | 1260 module | encode | decode |
717 -----------|------------|------------| 1261 -----------|------------|------------|
718 JSON | 7645.468 | 4208.613 | 1262 JSON 1.x | 4990.842 | 4088.813 |
719 JSON::DWIW | 40721.398 | 77101.176 | 1263 JSON::DWIW | 51653.990 | 71575.154 |
720 JSON::PC | 65948.176 | 78251.940 | 1264 JSON::PC | 65948.176 | 74631.744 |
721 JSON::Syck | 22844.793 | 26479.192 | 1265 JSON::PP | 8931.652 | 3817.168 |
1266 JSON::Syck | 24877.248 | 27776.848 |
722 JSON::XS | 388361.481 | 199728.762 | 1267 JSON::XS | 388361.481 | 227951.304 |
723 JSON::XS/2 | 218453.333 | 192399.266 | 1268 JSON::XS/2 | 227951.304 | 218453.333 |
724 JSON::XS/3 | 338250.323 | 192399.266 | 1269 JSON::XS/3 | 338250.323 | 218453.333 |
725 Storable | 15779.925 | 14169.946 | 1270 Storable | 16500.016 | 135300.129 |
726 -----------+------------+------------+ 1271 -----------+------------+------------+
727 1272
728That is, JSON::XS is about five times faster than JSON::DWIW on encoding, 1273That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
729about three times faster on decoding, and over fourty times faster 1274about three times faster on decoding, and over forty times faster
730than JSON, even with pretty-printing and key sorting. It also compares 1275than JSON, even with pretty-printing and key sorting. It also compares
731favourably to Storable for small amounts of data. 1276favourably to Storable for small amounts of data.
732 1277
733Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1278Using a longer test string (roughly 18KB, generated from Yahoo! Locals
734search API (http://nanoref.com/yahooapis/mgPdGg): 1279search API (L<http://dist.schmorp.de/misc/json/long.json>).
735 1280
736 module | encode | decode | 1281 module | encode | decode |
737 -----------|------------|------------| 1282 -----------|------------|------------|
738 JSON | 254.685 | 37.665 | 1283 JSON 1.x | 55.260 | 34.971 |
739 JSON::DWIW | 843.343 | 1049.731 | 1284 JSON::DWIW | 825.228 | 1082.513 |
740 JSON::PC | 3602.116 | 2307.352 | 1285 JSON::PC | 3571.444 | 2394.829 |
1286 JSON::PP | 210.987 | 32.574 |
741 JSON::Syck | 505.107 | 787.899 | 1287 JSON::Syck | 552.551 | 787.544 |
742 JSON::XS | 5747.196 | 3690.220 | 1288 JSON::XS | 5780.463 | 4854.519 |
743 JSON::XS/2 | 3968.121 | 3676.634 | 1289 JSON::XS/2 | 3869.998 | 4798.975 |
744 JSON::XS/3 | 6105.246 | 3662.508 | 1290 JSON::XS/3 | 5862.880 | 4798.975 |
745 Storable | 4417.337 | 5285.161 | 1291 Storable | 4445.002 | 5235.027 |
746 -----------+------------+------------+ 1292 -----------+------------+------------+
747 1293
748Again, JSON::XS leads by far (except for Storable which non-surprisingly 1294Again, JSON::XS leads by far (except for Storable which non-surprisingly
749decodes faster). 1295decodes faster).
750 1296
751On large strings containing lots of high unicode characters, some modules 1297On 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 1298(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 1299will be broken due to missing (or wrong) Unicode handling. Others refuse
754to decode or encode properly, so it was impossible to prepare a fair 1300to decode or encode properly, so it was impossible to prepare a fair
755comparison table for that case. 1301comparison table for that case.
756 1302
757 1303
758=head1 SECURITY CONSIDERATIONS 1304=head1 SECURITY CONSIDERATIONS
764any buffer overflows. Obviously, this module should ensure that and I am 1310any buffer overflows. Obviously, this module should ensure that and I am
765trying hard on making that true, but you never know. 1311trying hard on making that true, but you never know.
766 1312
767Second, you need to avoid resource-starving attacks. That means you should 1313Second, 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 1314limit 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 1315resources 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 1316can 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 1317usually 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 1318it 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 1319text, 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. 1320might want to check the size before you accept the string.
775 1321
776Third, JSON::XS recurses using the C stack when decoding objects and 1322Third, JSON::XS recurses using the C stack when decoding objects and
777arrays. The C stack is a limited resource: for instance, on my amd64 1323arrays. 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 1324machine 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 1325only 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 1326to free the temporary). If that is exceeded, the program crashes. To be
781conservative, the default nesting limit is set to 512. If your process 1327conservative, the default nesting limit is set to 512. If your process
782has a smaller stack, you should adjust this setting accordingly with the 1328has a smaller stack, you should adjust this setting accordingly with the
783C<max_depth> method. 1329C<max_depth> method.
784 1330
785And last but least, something else could bomb you that I forgot to think 1331Something 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, 1332case, you get to keep the pieces. I am always open for hints, though...
787though... 1333
1334Also keep in mind that JSON::XS might leak contents of your Perl data
1335structures in its error messages, so when you serialise sensitive
1336information you might want to make sure that exceptions thrown by JSON::XS
1337will not end up in front of untrusted eyes.
788 1338
789If you are using JSON::XS to return packets to consumption 1339If you are using JSON::XS to return packets to consumption
790by javascript scripts in a browser you should have a look at 1340by JavaScript scripts in a browser you should have a look at
791L<http://jpsykes.com/47/practical-csrf-and-json-security> to see wether 1341L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
792you are vulnerable to some common attack vectors (which really are browser 1342you 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 1343design 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 1344browser developers care only for features, not about getting security
795right). 1345right).
796 1346
797 1347
1348=head1 THREADS
1349
1350This module is I<not> guaranteed to be thread safe and there are no
1351plans to change this until Perl gets thread support (as opposed to the
1352horribly slow so-called "threads" which are simply slow and bloated
1353process simulations - use fork, it's I<much> faster, cheaper, better).
1354
1355(It might actually work, but you have been warned).
1356
1357
798=head1 BUGS 1358=head1 BUGS
799 1359
800While the goal of this module is to be correct, that unfortunately does 1360While 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 1361not mean it's bug-free, only that I think its design is bug-free. If you
802still relatively early in its development. If you keep reporting bugs they 1362keep reporting bugs they will be fixed swiftly, though.
803will be fixed swiftly, though. 1363
1364Please refrain from using rt.cpan.org or any other bug reporting
1365service. I put the contact address into my modules for a reason.
804 1366
805=cut 1367=cut
806 1368
807our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" }; 1369our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
808our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" }; 1370our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
825 "--" => sub { $_[0] = ${$_[0]} - 1 }, 1387 "--" => sub { $_[0] = ${$_[0]} - 1 },
826 fallback => 1; 1388 fallback => 1;
827 1389
8281; 13901;
829 1391
1392=head1 SEE ALSO
1393
1394The F<json_xs> command line utility for quick experiments.
1395
830=head1 AUTHOR 1396=head1 AUTHOR
831 1397
832 Marc Lehmann <schmorp@schmorp.de> 1398 Marc Lehmann <schmorp@schmorp.de>
833 http://home.schmorp.de/ 1399 http://home.schmorp.de/
834 1400

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