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1NAME 1NAME
2 JSON::XS - JSON serialising/deserialising, done correctly and fast 2 JSON::XS - JSON serialising/deserialising, done correctly and fast
3 3
4 JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
5 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
6
4SYNOPSIS 7SYNOPSIS
5 use JSON::XS; 8 use JSON::XS;
6 9
7 # exported functions, they croak on error 10 # exported functions, they croak on error
8 # and expect/generate UTF-8 11 # and expect/generate UTF-8
9 12
10 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 13 $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
11 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 14 $perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
12
13 # objToJson and jsonToObj aliases to to_json and from_json
14 # are exported for compatibility to the JSON module,
15 # but should not be used in new code.
16 15
17 # OO-interface 16 # OO-interface
18 17
19 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 18 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
20 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 19 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
21 $perl_scalar = $coder->decode ($unicode_json_text); 20 $perl_scalar = $coder->decode ($unicode_json_text);
21
22 # Note that JSON version 2.0 and above will automatically use JSON::XS
23 # if available, at virtually no speed overhead either, so you should
24 # be able to just:
25
26 use JSON;
27
28 # and do the same things, except that you have a pure-perl fallback now.
22 29
23DESCRIPTION 30DESCRIPTION
24 This module converts Perl data structures to JSON and vice versa. Its 31 This module converts Perl data structures to JSON and vice versa. Its
25 primary goal is to be *correct* and its secondary goal is to be *fast*. 32 primary goal is to be *correct* and its secondary goal is to be *fast*.
26 To reach the latter goal it was written in C. 33 To reach the latter goal it was written in C.
34
35 Beginning with version 2.0 of the JSON module, when both JSON and
36 JSON::XS are installed, then JSON will fall back on JSON::XS (this can
37 be overridden) with no overhead due to emulation (by inheriting
38 constructor and methods). If JSON::XS is not available, it will fall
39 back to the compatible JSON::PP module as backend, so using JSON instead
40 of JSON::XS gives you a portable JSON API that can be fast when you need
41 and doesn't require a C compiler when that is a problem.
27 42
28 As this is the n-th-something JSON module on CPAN, what was the reason 43 As this is the n-th-something JSON module on CPAN, what was the reason
29 to write yet another JSON module? While it seems there are many JSON 44 to write yet another JSON module? While it seems there are many JSON
30 modules, none of them correctly handle all corner cases, and in most 45 modules, none of them correctly handle all corner cases, and in most
31 cases their maintainers are unresponsive, gone missing, or not listening 46 cases their maintainers are unresponsive, gone missing, or not listening
32 to bug reports for other reasons. 47 to bug reports for other reasons.
33 48
34 See COMPARISON, below, for a comparison to some other JSON modules.
35
36 See MAPPING, below, on how JSON::XS maps perl values to JSON values and 49 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
37 vice versa. 50 vice versa.
38 51
39 FEATURES 52 FEATURES
40 * correct unicode handling 53 * correct Unicode handling
54
41 This module knows how to handle Unicode, and even documents how and 55 This module knows how to handle Unicode, documents how and when it
42 when it does so. 56 does so, and even documents what "correct" means.
43 57
44 * round-trip integrity 58 * round-trip integrity
59
45 When you serialise a perl data structure using only datatypes 60 When you serialise a perl data structure using only data types
46 supported by JSON, the deserialised data structure is identical on 61 supported by JSON and Perl, the deserialised data structure is
47 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" 62 identical on the Perl level. (e.g. the string "2.0" doesn't suddenly
48 just because it looks like a number). 63 become "2" just because it looks like a number). There *are* minor
64 exceptions to this, read the MAPPING section below to learn about
65 those.
49 66
50 * strict checking of JSON correctness 67 * strict checking of JSON correctness
68
51 There is no guessing, no generating of illegal JSON texts by 69 There is no guessing, no generating of illegal JSON texts by
52 default, and only JSON is accepted as input by default (the latter 70 default, and only JSON is accepted as input by default (the latter
53 is a security feature). 71 is a security feature).
54 72
55 * fast 73 * fast
56 Compared to other JSON modules, this module compares favourably in
57 terms of speed, too.
58 74
75 Compared to other JSON modules and other serialisers such as
76 Storable, this module usually compares favourably in terms of speed,
77 too.
78
59 * simple to use 79 * simple to use
80
60 This module has both a simple functional interface as well as an OO 81 This module has both a simple functional interface as well as an
61 interface. 82 object oriented interface.
62 83
63 * reasonably versatile output formats 84 * reasonably versatile output formats
85
64 You can choose between the most compact guarenteed single-line 86 You can choose between the most compact guaranteed-single-line
65 format possible (nice for simple line-based protocols), a pure-ascii 87 format possible (nice for simple line-based protocols), a pure-ASCII
66 format (for when your transport is not 8-bit clean, still supports 88 format (for when your transport is not 8-bit clean, still supports
67 the whole unicode range), or a pretty-printed format (for when you 89 the whole Unicode range), or a pretty-printed format (for when you
68 want to read that stuff). Or you can combine those features in 90 want to read that stuff). Or you can combine those features in
69 whatever way you like. 91 whatever way you like.
70 92
71FUNCTIONAL INTERFACE 93FUNCTIONAL INTERFACE
72 The following convinience methods are provided by this module. They are 94 The following convenience methods are provided by this module. They are
73 exported by default: 95 exported by default:
74 96
75 $json_text = to_json $perl_scalar 97 $json_text = encode_json $perl_scalar
76 Converts the given Perl data structure (a simple scalar or a 98 Converts the given Perl data structure to a UTF-8 encoded, binary
77 reference to a hash or array) to a UTF-8 encoded, binary string
78 (that is, the string contains octets only). Croaks on error. 99 string (that is, the string contains octets only). Croaks on error.
79 100
80 This function call is functionally identical to: 101 This function call is functionally identical to:
81 102
82 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 103 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
83 104
84 except being faster. 105 Except being faster.
85 106
86 $perl_scalar = from_json $json_text 107 $perl_scalar = decode_json $json_text
87 The opposite of "to_json": expects an UTF-8 (binary) string and 108 The opposite of "encode_json": expects an UTF-8 (binary) string and
88 tries to parse that as an UTF-8 encoded JSON text, returning the 109 tries to parse that as an UTF-8 encoded JSON text, returning the
89 resulting simple scalar or reference. Croaks on error. 110 resulting reference. Croaks on error.
90 111
91 This function call is functionally identical to: 112 This function call is functionally identical to:
92 113
93 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 114 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
94 115
95 except being faster. 116 Except being faster.
117
118A FEW NOTES ON UNICODE AND PERL
119 Since this often leads to confusion, here are a few very clear words on
120 how Unicode works in Perl, modulo bugs.
121
122 1. Perl strings can store characters with ordinal values > 255.
123 This enables you to store Unicode characters as single characters in
124 a Perl string - very natural.
125
126 2. Perl does *not* associate an encoding with your strings.
127 ... until you force it to, e.g. when matching it against a regex, or
128 printing the scalar to a file, in which case Perl either interprets
129 your string as locale-encoded text, octets/binary, or as Unicode,
130 depending on various settings. In no case is an encoding stored
131 together with your data, it is *use* that decides encoding, not any
132 magical meta data.
133
134 3. The internal utf-8 flag has no meaning with regards to the encoding
135 of your string.
136 Just ignore that flag unless you debug a Perl bug, a module written
137 in XS or want to dive into the internals of perl. Otherwise it will
138 only confuse you, as, despite the name, it says nothing about how
139 your string is encoded. You can have Unicode strings with that flag
140 set, with that flag clear, and you can have binary data with that
141 flag set and that flag clear. Other possibilities exist, too.
142
143 If you didn't know about that flag, just the better, pretend it
144 doesn't exist.
145
146 4. A "Unicode String" is simply a string where each character can be
147 validly interpreted as a Unicode code point.
148 If you have UTF-8 encoded data, it is no longer a Unicode string,
149 but a Unicode string encoded in UTF-8, giving you a binary string.
150
151 5. A string containing "high" (> 255) character values is *not* a UTF-8
152 string.
153 It's a fact. Learn to live with it.
154
155 I hope this helps :)
96 156
97OBJECT-ORIENTED INTERFACE 157OBJECT-ORIENTED INTERFACE
98 The object oriented interface lets you configure your own encoding or 158 The object oriented interface lets you configure your own encoding or
99 decoding style, within the limits of supported formats. 159 decoding style, within the limits of supported formats.
100 160
… …
108 168
109 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) 169 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
110 => {"a": [1, 2]} 170 => {"a": [1, 2]}
111 171
112 $json = $json->ascii ([$enable]) 172 $json = $json->ascii ([$enable])
173 $enabled = $json->get_ascii
113 If $enable is true (or missing), then the "encode" method will not 174 If $enable is true (or missing), then the "encode" method will not
114 generate characters outside the code range 0..127 (which is ASCII). 175 generate characters outside the code range 0..127 (which is ASCII).
115 Any unicode characters outside that range will be escaped using 176 Any Unicode characters outside that range will be escaped using
116 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL 177 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
117 escape sequence, as per RFC4627. 178 escape sequence, as per RFC4627. The resulting encoded JSON text can
179 be treated as a native Unicode string, an ascii-encoded,
180 latin1-encoded or UTF-8 encoded string, or any other superset of
181 ASCII.
118 182
119 If $enable is false, then the "encode" method will not escape 183 If $enable is false, then the "encode" method will not escape
120 Unicode characters unless required by the JSON syntax. This results 184 Unicode characters unless required by the JSON syntax or other
121 in a faster and more compact format. 185 flags. This results in a faster and more compact format.
186
187 See also the section *ENCODING/CODESET FLAG NOTES* later in this
188 document.
189
190 The main use for this flag is to produce JSON texts that can be
191 transmitted over a 7-bit channel, as the encoded JSON texts will not
192 contain any 8 bit characters.
122 193
123 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 194 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
124 => ["\ud801\udc01"] 195 => ["\ud801\udc01"]
125 196
197 $json = $json->latin1 ([$enable])
198 $enabled = $json->get_latin1
199 If $enable is true (or missing), then the "encode" method will
200 encode the resulting JSON text as latin1 (or iso-8859-1), escaping
201 any characters outside the code range 0..255. The resulting string
202 can be treated as a latin1-encoded JSON text or a native Unicode
203 string. The "decode" method will not be affected in any way by this
204 flag, as "decode" by default expects Unicode, which is a strict
205 superset of latin1.
206
207 If $enable is false, then the "encode" method will not escape
208 Unicode characters unless required by the JSON syntax or other
209 flags.
210
211 See also the section *ENCODING/CODESET FLAG NOTES* later in this
212 document.
213
214 The main use for this flag is efficiently encoding binary data as
215 JSON text, as most octets will not be escaped, resulting in a
216 smaller encoded size. The disadvantage is that the resulting JSON
217 text is encoded in latin1 (and must correctly be treated as such
218 when storing and transferring), a rare encoding for JSON. It is
219 therefore most useful when you want to store data structures known
220 to contain binary data efficiently in files or databases, not when
221 talking to other JSON encoders/decoders.
222
223 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
224 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
225
126 $json = $json->utf8 ([$enable]) 226 $json = $json->utf8 ([$enable])
227 $enabled = $json->get_utf8
127 If $enable is true (or missing), then the "encode" method will 228 If $enable is true (or missing), then the "encode" method will
128 encode the JSON result into UTF-8, as required by many protocols, 229 encode the JSON result into UTF-8, as required by many protocols,
129 while the "decode" method expects to be handled an UTF-8-encoded 230 while the "decode" method expects to be handled an UTF-8-encoded
130 string. Please note that UTF-8-encoded strings do not contain any 231 string. Please note that UTF-8-encoded strings do not contain any
131 characters outside the range 0..255, they are thus useful for 232 characters outside the range 0..255, they are thus useful for
132 bytewise/binary I/O. In future versions, enabling this option might 233 bytewise/binary I/O. In future versions, enabling this option might
133 enable autodetection of the UTF-16 and UTF-32 encoding families, as 234 enable autodetection of the UTF-16 and UTF-32 encoding families, as
134 described in RFC4627. 235 described in RFC4627.
135 236
136 If $enable is false, then the "encode" method will return the JSON 237 If $enable is false, then the "encode" method will return the JSON
137 string as a (non-encoded) unicode string, while "decode" expects 238 string as a (non-encoded) Unicode string, while "decode" expects
138 thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or 239 thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or
139 UTF-16) needs to be done yourself, e.g. using the Encode module. 240 UTF-16) needs to be done yourself, e.g. using the Encode module.
241
242 See also the section *ENCODING/CODESET FLAG NOTES* later in this
243 document.
140 244
141 Example, output UTF-16BE-encoded JSON: 245 Example, output UTF-16BE-encoded JSON:
142 246
143 use Encode; 247 use Encode;
144 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); 248 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
… …
163 2 267 2
164 ] 268 ]
165 } 269 }
166 270
167 $json = $json->indent ([$enable]) 271 $json = $json->indent ([$enable])
272 $enabled = $json->get_indent
168 If $enable is true (or missing), then the "encode" method will use a 273 If $enable is true (or missing), then the "encode" method will use a
169 multiline format as output, putting every array member or 274 multiline format as output, putting every array member or
170 object/hash key-value pair into its own line, identing them 275 object/hash key-value pair into its own line, indenting them
171 properly. 276 properly.
172 277
173 If $enable is false, no newlines or indenting will be produced, and 278 If $enable is false, no newlines or indenting will be produced, and
174 the resulting JSON text is guarenteed not to contain any "newlines". 279 the resulting JSON text is guaranteed not to contain any "newlines".
175 280
176 This setting has no effect when decoding JSON texts. 281 This setting has no effect when decoding JSON texts.
177 282
178 $json = $json->space_before ([$enable]) 283 $json = $json->space_before ([$enable])
284 $enabled = $json->get_space_before
179 If $enable is true (or missing), then the "encode" method will add 285 If $enable is true (or missing), then the "encode" method will add
180 an extra optional space before the ":" separating keys from values 286 an extra optional space before the ":" separating keys from values
181 in JSON objects. 287 in JSON objects.
182 288
183 If $enable is false, then the "encode" method will not add any extra 289 If $enable is false, then the "encode" method will not add any extra
… …
189 Example, space_before enabled, space_after and indent disabled: 295 Example, space_before enabled, space_after and indent disabled:
190 296
191 {"key" :"value"} 297 {"key" :"value"}
192 298
193 $json = $json->space_after ([$enable]) 299 $json = $json->space_after ([$enable])
300 $enabled = $json->get_space_after
194 If $enable is true (or missing), then the "encode" method will add 301 If $enable is true (or missing), then the "encode" method will add
195 an extra optional space after the ":" separating keys from values in 302 an extra optional space after the ":" separating keys from values in
196 JSON objects and extra whitespace after the "," separating key-value 303 JSON objects and extra whitespace after the "," separating key-value
197 pairs and array members. 304 pairs and array members.
198 305
… …
203 310
204 Example, space_before and indent disabled, space_after enabled: 311 Example, space_before and indent disabled, space_after enabled:
205 312
206 {"key": "value"} 313 {"key": "value"}
207 314
315 $json = $json->relaxed ([$enable])
316 $enabled = $json->get_relaxed
317 If $enable is true (or missing), then "decode" will accept some
318 extensions to normal JSON syntax (see below). "encode" will not be
319 affected in anyway. *Be aware that this option makes you accept
320 invalid JSON texts as if they were valid!*. I suggest only to use
321 this option to parse application-specific files written by humans
322 (configuration files, resource files etc.)
323
324 If $enable is false (the default), then "decode" will only accept
325 valid JSON texts.
326
327 Currently accepted extensions are:
328
329 * list items can have an end-comma
330
331 JSON *separates* array elements and key-value pairs with commas.
332 This can be annoying if you write JSON texts manually and want
333 to be able to quickly append elements, so this extension accepts
334 comma at the end of such items not just between them:
335
336 [
337 1,
338 2, <- this comma not normally allowed
339 ]
340 {
341 "k1": "v1",
342 "k2": "v2", <- this comma not normally allowed
343 }
344
345 * shell-style '#'-comments
346
347 Whenever JSON allows whitespace, shell-style comments are
348 additionally allowed. They are terminated by the first
349 carriage-return or line-feed character, after which more
350 white-space and comments are allowed.
351
352 [
353 1, # this comment not allowed in JSON
354 # neither this one...
355 ]
356
208 $json = $json->canonical ([$enable]) 357 $json = $json->canonical ([$enable])
358 $enabled = $json->get_canonical
209 If $enable is true (or missing), then the "encode" method will 359 If $enable is true (or missing), then the "encode" method will
210 output JSON objects by sorting their keys. This is adding a 360 output JSON objects by sorting their keys. This is adding a
211 comparatively high overhead. 361 comparatively high overhead.
212 362
213 If $enable is false, then the "encode" method will output key-value 363 If $enable is false, then the "encode" method will output key-value
214 pairs in the order Perl stores them (which will likely change 364 pairs in the order Perl stores them (which will likely change
215 between runs of the same script). 365 between runs of the same script, and can change even within the same
366 run from 5.18 onwards).
216 367
217 This option is useful if you want the same data structure to be 368 This option is useful if you want the same data structure to be
218 encoded as the same JSON text (given the same overall settings). If 369 encoded as the same JSON text (given the same overall settings). If
219 it is disabled, the same hash migh be encoded differently even if 370 it is disabled, the same hash might be encoded differently even if
220 contains the same data, as key-value pairs have no inherent ordering 371 contains the same data, as key-value pairs have no inherent ordering
221 in Perl. 372 in Perl.
222 373
223 This setting has no effect when decoding JSON texts. 374 This setting has no effect when decoding JSON texts.
224 375
376 This setting has currently no effect on tied hashes.
377
225 $json = $json->allow_nonref ([$enable]) 378 $json = $json->allow_nonref ([$enable])
379 $enabled = $json->get_allow_nonref
226 If $enable is true (or missing), then the "encode" method can 380 If $enable is true (or missing), then the "encode" method can
227 convert a non-reference into its corresponding string, number or 381 convert a non-reference into its corresponding string, number or
228 null JSON value, which is an extension to RFC4627. Likewise, 382 null JSON value, which is an extension to RFC4627. Likewise,
229 "decode" will accept those JSON values instead of croaking. 383 "decode" will accept those JSON values instead of croaking.
230 384
… …
237 "allow_nonref", resulting in an invalid JSON text: 391 "allow_nonref", resulting in an invalid JSON text:
238 392
239 JSON::XS->new->allow_nonref->encode ("Hello, World!") 393 JSON::XS->new->allow_nonref->encode ("Hello, World!")
240 => "Hello, World!" 394 => "Hello, World!"
241 395
396 $json = $json->allow_unknown ([$enable])
397 $enabled = $json->get_allow_unknown
398 If $enable is true (or missing), then "encode" will *not* throw an
399 exception when it encounters values it cannot represent in JSON (for
400 example, filehandles) but instead will encode a JSON "null" value.
401 Note that blessed objects are not included here and are handled
402 separately by c<allow_nonref>.
403
404 If $enable is false (the default), then "encode" will throw an
405 exception when it encounters anything it cannot encode as JSON.
406
407 This option does not affect "decode" in any way, and it is
408 recommended to leave it off unless you know your communications
409 partner.
410
411 $json = $json->allow_blessed ([$enable])
412 $enabled = $json->get_allow_blessed
413 See "OBJECT SERIALISATION" for details.
414
415 If $enable is true (or missing), then the "encode" method will not
416 barf when it encounters a blessed reference that it cannot convert
417 otherwise. Instead, a JSON "null" value is encoded instead of the
418 object.
419
420 If $enable is false (the default), then "encode" will throw an
421 exception when it encounters a blessed object that it cannot convert
422 otherwise.
423
424 This setting has no effect on "decode".
425
426 $json = $json->convert_blessed ([$enable])
427 $enabled = $json->get_convert_blessed
428 See "OBJECT SERIALISATION" for details.
429
430 If $enable is true (or missing), then "encode", upon encountering a
431 blessed object, will check for the availability of the "TO_JSON"
432 method on the object's class. If found, it will be called in scalar
433 context and the resulting scalar will be encoded instead of the
434 object.
435
436 The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
437 returns other blessed objects, those will be handled in the same
438 way. "TO_JSON" must take care of not causing an endless recursion
439 cycle (== crash) in this case. The name of "TO_JSON" was chosen
440 because other methods called by the Perl core (== not by the user of
441 the object) are usually in upper case letters and to avoid
442 collisions with any "to_json" function or method.
443
444 If $enable is false (the default), then "encode" will not consider
445 this type of conversion.
446
447 This setting has no effect on "decode".
448
449 $json = $json->allow_tags ([$enable])
450 $enabled = $json->allow_tags
451 See "OBJECT SERIALISATION" for details.
452
453 If $enable is true (or missing), then "encode", upon encountering a
454 blessed object, will check for the availability of the "FREEZE"
455 method on the object's class. If found, it will be used to serialise
456 the object into a nonstandard tagged JSON value (that JSON decoders
457 cannot decode).
458
459 It also causes "decode" to parse such tagged JSON values and
460 deserialise them via a call to the "THAW" method.
461
462 If $enable is false (the default), then "encode" will not consider
463 this type of conversion, and tagged JSON values will cause a parse
464 error in "decode", as if tags were not part of the grammar.
465
466 $json = $json->filter_json_object ([$coderef->($hashref)])
467 When $coderef is specified, it will be called from "decode" each
468 time it decodes a JSON object. The only argument is a reference to
469 the newly-created hash. If the code references returns a single
470 scalar (which need not be a reference), this value (i.e. a copy of
471 that scalar to avoid aliasing) is inserted into the deserialised
472 data structure. If it returns an empty list (NOTE: *not* "undef",
473 which is a valid scalar), the original deserialised hash will be
474 inserted. This setting can slow down decoding considerably.
475
476 When $coderef is omitted or undefined, any existing callback will be
477 removed and "decode" will not change the deserialised hash in any
478 way.
479
480 Example, convert all JSON objects into the integer 5:
481
482 my $js = JSON::XS->new->filter_json_object (sub { 5 });
483 # returns [5]
484 $js->decode ('[{}]')
485 # throw an exception because allow_nonref is not enabled
486 # so a lone 5 is not allowed.
487 $js->decode ('{"a":1, "b":2}');
488
489 $json = $json->filter_json_single_key_object ($key [=>
490 $coderef->($value)])
491 Works remotely similar to "filter_json_object", but is only called
492 for JSON objects having a single key named $key.
493
494 This $coderef is called before the one specified via
495 "filter_json_object", if any. It gets passed the single value in the
496 JSON object. If it returns a single value, it will be inserted into
497 the data structure. If it returns nothing (not even "undef" but the
498 empty list), the callback from "filter_json_object" will be called
499 next, as if no single-key callback were specified.
500
501 If $coderef is omitted or undefined, the corresponding callback will
502 be disabled. There can only ever be one callback for a given key.
503
504 As this callback gets called less often then the
505 "filter_json_object" one, decoding speed will not usually suffer as
506 much. Therefore, single-key objects make excellent targets to
507 serialise Perl objects into, especially as single-key JSON objects
508 are as close to the type-tagged value concept as JSON gets (it's
509 basically an ID/VALUE tuple). Of course, JSON does not support this
510 in any way, so you need to make sure your data never looks like a
511 serialised Perl hash.
512
513 Typical names for the single object key are "__class_whatever__", or
514 "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
515 things like "__class_md5sum(classname)__", to reduce the risk of
516 clashing with real hashes.
517
518 Example, decode JSON objects of the form "{ "__widget__" => <id> }"
519 into the corresponding $WIDGET{<id>} object:
520
521 # return whatever is in $WIDGET{5}:
522 JSON::XS
523 ->new
524 ->filter_json_single_key_object (__widget__ => sub {
525 $WIDGET{ $_[0] }
526 })
527 ->decode ('{"__widget__": 5')
528
529 # this can be used with a TO_JSON method in some "widget" class
530 # for serialisation to json:
531 sub WidgetBase::TO_JSON {
532 my ($self) = @_;
533
534 unless ($self->{id}) {
535 $self->{id} = ..get..some..id..;
536 $WIDGET{$self->{id}} = $self;
537 }
538
539 { __widget__ => $self->{id} }
540 }
541
242 $json = $json->shrink ([$enable]) 542 $json = $json->shrink ([$enable])
543 $enabled = $json->get_shrink
243 Perl usually over-allocates memory a bit when allocating space for 544 Perl usually over-allocates memory a bit when allocating space for
244 strings. This flag optionally resizes strings generated by either 545 strings. This flag optionally resizes strings generated by either
245 "encode" or "decode" to their minimum size possible. This can save 546 "encode" or "decode" to their minimum size possible. This can save
246 memory when your JSON texts are either very very long or you have 547 memory when your JSON texts are either very very long or you have
247 many short strings. It will also try to downgrade any strings to 548 many short strings. It will also try to downgrade any strings to
248 octet-form if possible: perl stores strings internally either in an 549 octet-form if possible: perl stores strings internally either in an
249 encoding called UTF-X or in octet-form. The latter cannot store 550 encoding called UTF-X or in octet-form. The latter cannot store
250 everything but uses less space in general. 551 everything but uses less space in general (and some buggy Perl or C
552 code might even rely on that internal representation being used).
553
554 The actual definition of what shrink does might change in future
555 versions, but it will always try to save space at the expense of
556 time.
251 557
252 If $enable is true (or missing), the string returned by "encode" 558 If $enable is true (or missing), the string returned by "encode"
253 will be shrunk-to-fit, while all strings generated by "decode" will 559 will be shrunk-to-fit, while all strings generated by "decode" will
254 also be shrunk-to-fit. 560 also be shrunk-to-fit.
255 561
… …
260 converting strings that look like integers or floats into integers 566 converting strings that look like integers or floats into integers
261 or floats internally (there is no difference on the Perl level), 567 or floats internally (there is no difference on the Perl level),
262 saving space. 568 saving space.
263 569
264 $json = $json->max_depth ([$maximum_nesting_depth]) 570 $json = $json->max_depth ([$maximum_nesting_depth])
571 $max_depth = $json->get_max_depth
265 Sets the maximum nesting level (default 8192) accepted while 572 Sets the maximum nesting level (default 512) accepted while encoding
266 encoding or decoding. If the JSON text or Perl data structure has an 573 or decoding. If a higher nesting level is detected in JSON text or a
267 equal or higher nesting level then this limit, then the encoder and 574 Perl data structure, then the encoder and decoder will stop and
268 decoder will stop and croak at that point. 575 croak at that point.
269 576
270 Nesting level is defined by number of hash- or arrayrefs that the 577 Nesting level is defined by number of hash- or arrayrefs that the
271 encoder needs to traverse to reach a given point or the number of 578 encoder needs to traverse to reach a given point or the number of
272 "{" or "[" characters without their matching closing parenthesis 579 "{" or "[" characters without their matching closing parenthesis
273 crossed to reach a given character in a string. 580 crossed to reach a given character in a string.
274 581
275 Setting the maximum depth to one disallows any nesting, so that 582 Setting the maximum depth to one disallows any nesting, so that
276 ensures that the object is only a single hash/object or array. 583 ensures that the object is only a single hash/object or array.
277 584
278 The argument to "max_depth" will be rounded up to the next nearest 585 If no argument is given, the highest possible setting will be used,
279 power of two. 586 which is rarely useful.
587
588 Note that nesting is implemented by recursion in C. The default
589 value has been chosen to be as large as typical operating systems
590 allow without crashing.
280 591
281 See SECURITY CONSIDERATIONS, below, for more info on why this is 592 See SECURITY CONSIDERATIONS, below, for more info on why this is
282 useful. 593 useful.
283 594
595 $json = $json->max_size ([$maximum_string_size])
596 $max_size = $json->get_max_size
597 Set the maximum length a JSON text may have (in bytes) where
598 decoding is being attempted. The default is 0, meaning no limit.
599 When "decode" is called on a string that is longer then this many
600 bytes, it will not attempt to decode the string but throw an
601 exception. This setting has no effect on "encode" (yet).
602
603 If no argument is given, the limit check will be deactivated (same
604 as when 0 is specified).
605
606 See SECURITY CONSIDERATIONS, below, for more info on why this is
607 useful.
608
284 $json_text = $json->encode ($perl_scalar) 609 $json_text = $json->encode ($perl_scalar)
285 Converts the given Perl data structure (a simple scalar or a 610 Converts the given Perl value or data structure to its JSON
286 reference to a hash or array) to its JSON representation. Simple 611 representation. Croaks on error.
287 scalars will be converted into JSON string or number sequences,
288 while references to arrays become JSON arrays and references to
289 hashes become JSON objects. Undefined Perl values (e.g. "undef")
290 become JSON "null" values. Neither "true" nor "false" values will be
291 generated.
292 612
293 $perl_scalar = $json->decode ($json_text) 613 $perl_scalar = $json->decode ($json_text)
294 The opposite of "encode": expects a JSON text and tries to parse it, 614 The opposite of "encode": expects a JSON text and tries to parse it,
295 returning the resulting simple scalar or reference. Croaks on error. 615 returning the resulting simple scalar or reference. Croaks on error.
296 616
297 JSON numbers and strings become simple Perl scalars. JSON arrays 617 ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
298 become Perl arrayrefs and JSON objects become Perl hashrefs. "true" 618 This works like the "decode" method, but instead of raising an
299 becomes 1, "false" becomes 0 and "null" becomes "undef". 619 exception when there is trailing garbage after the first JSON
620 object, it will silently stop parsing there and return the number of
621 characters consumed so far.
622
623 This is useful if your JSON texts are not delimited by an outer
624 protocol and you need to know where the JSON text ends.
625
626 JSON::XS->new->decode_prefix ("[1] the tail")
627 => ([], 3)
628
629INCREMENTAL PARSING
630 In some cases, there is the need for incremental parsing of JSON texts.
631 While this module always has to keep both JSON text and resulting Perl
632 data structure in memory at one time, it does allow you to parse a JSON
633 stream incrementally. It does so by accumulating text until it has a
634 full JSON object, which it then can decode. This process is similar to
635 using "decode_prefix" to see if a full JSON object is available, but is
636 much more efficient (and can be implemented with a minimum of method
637 calls).
638
639 JSON::XS will only attempt to parse the JSON text once it is sure it has
640 enough text to get a decisive result, using a very simple but truly
641 incremental parser. This means that it sometimes won't stop as early as
642 the full parser, for example, it doesn't detect mismatched parentheses.
643 The only thing it guarantees is that it starts decoding as soon as a
644 syntactically valid JSON text has been seen. This means you need to set
645 resource limits (e.g. "max_size") to ensure the parser will stop parsing
646 in the presence if syntax errors.
647
648 The following methods implement this incremental parser.
649
650 [void, scalar or list context] = $json->incr_parse ([$string])
651 This is the central parsing function. It can both append new text
652 and extract objects from the stream accumulated so far (both of
653 these functions are optional).
654
655 If $string is given, then this string is appended to the already
656 existing JSON fragment stored in the $json object.
657
658 After that, if the function is called in void context, it will
659 simply return without doing anything further. This can be used to
660 add more text in as many chunks as you want.
661
662 If the method is called in scalar context, then it will try to
663 extract exactly *one* JSON object. If that is successful, it will
664 return this object, otherwise it will return "undef". If there is a
665 parse error, this method will croak just as "decode" would do (one
666 can then use "incr_skip" to skip the erroneous part). This is the
667 most common way of using the method.
668
669 And finally, in list context, it will try to extract as many objects
670 from the stream as it can find and return them, or the empty list
671 otherwise. For this to work, there must be no separators between the
672 JSON objects or arrays, instead they must be concatenated
673 back-to-back. If an error occurs, an exception will be raised as in
674 the scalar context case. Note that in this case, any
675 previously-parsed JSON texts will be lost.
676
677 Example: Parse some JSON arrays/objects in a given string and return
678 them.
679
680 my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
681
682 $lvalue_string = $json->incr_text
683 This method returns the currently stored JSON fragment as an lvalue,
684 that is, you can manipulate it. This *only* works when a preceding
685 call to "incr_parse" in *scalar context* successfully returned an
686 object. Under all other circumstances you must not call this
687 function (I mean it. although in simple tests it might actually
688 work, it *will* fail under real world conditions). As a special
689 exception, you can also call this method before having parsed
690 anything.
691
692 This function is useful in two cases: a) finding the trailing text
693 after a JSON object or b) parsing multiple JSON objects separated by
694 non-JSON text (such as commas).
695
696 $json->incr_skip
697 This will reset the state of the incremental parser and will remove
698 the parsed text from the input buffer so far. This is useful after
699 "incr_parse" died, in which case the input buffer and incremental
700 parser state is left unchanged, to skip the text parsed so far and
701 to reset the parse state.
702
703 The difference to "incr_reset" is that only text until the parse
704 error occurred is removed.
705
706 $json->incr_reset
707 This completely resets the incremental parser, that is, after this
708 call, it will be as if the parser had never parsed anything.
709
710 This is useful if you want to repeatedly parse JSON objects and want
711 to ignore any trailing data, which means you have to reset the
712 parser after each successful decode.
713
714 LIMITATIONS
715 All options that affect decoding are supported, except "allow_nonref".
716 The reason for this is that it cannot be made to work sensibly: JSON
717 objects and arrays are self-delimited, i.e. you can concatenate them
718 back to back and still decode them perfectly. This does not hold true
719 for JSON numbers, however.
720
721 For example, is the string 1 a single JSON number, or is it simply the
722 start of 12? Or is 12 a single JSON number, or the concatenation of 1
723 and 2? In neither case you can tell, and this is why JSON::XS takes the
724 conservative route and disallows this case.
725
726 EXAMPLES
727 Some examples will make all this clearer. First, a simple example that
728 works similarly to "decode_prefix": We want to decode the JSON object at
729 the start of a string and identify the portion after the JSON object:
730
731 my $text = "[1,2,3] hello";
732
733 my $json = new JSON::XS;
734
735 my $obj = $json->incr_parse ($text)
736 or die "expected JSON object or array at beginning of string";
737
738 my $tail = $json->incr_text;
739 # $tail now contains " hello"
740
741 Easy, isn't it?
742
743 Now for a more complicated example: Imagine a hypothetical protocol
744 where you read some requests from a TCP stream, and each request is a
745 JSON array, without any separation between them (in fact, it is often
746 useful to use newlines as "separators", as these get interpreted as
747 whitespace at the start of the JSON text, which makes it possible to
748 test said protocol with "telnet"...).
749
750 Here is how you'd do it (it is trivial to write this in an event-based
751 manner):
752
753 my $json = new JSON::XS;
754
755 # read some data from the socket
756 while (sysread $socket, my $buf, 4096) {
757
758 # split and decode as many requests as possible
759 for my $request ($json->incr_parse ($buf)) {
760 # act on the $request
761 }
762 }
763
764 Another complicated example: Assume you have a string with JSON objects
765 or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
766 [3]"). To parse them, we have to skip the commas between the JSON texts,
767 and here is where the lvalue-ness of "incr_text" comes in useful:
768
769 my $text = "[1],[2], [3]";
770 my $json = new JSON::XS;
771
772 # void context, so no parsing done
773 $json->incr_parse ($text);
774
775 # now extract as many objects as possible. note the
776 # use of scalar context so incr_text can be called.
777 while (my $obj = $json->incr_parse) {
778 # do something with $obj
779
780 # now skip the optional comma
781 $json->incr_text =~ s/^ \s* , //x;
782 }
783
784 Now lets go for a very complex example: Assume that you have a gigantic
785 JSON array-of-objects, many gigabytes in size, and you want to parse it,
786 but you cannot load it into memory fully (this has actually happened in
787 the real world :).
788
789 Well, you lost, you have to implement your own JSON parser. But JSON::XS
790 can still help you: You implement a (very simple) array parser and let
791 JSON decode the array elements, which are all full JSON objects on their
792 own (this wouldn't work if the array elements could be JSON numbers, for
793 example):
794
795 my $json = new JSON::XS;
796
797 # open the monster
798 open my $fh, "<bigfile.json"
799 or die "bigfile: $!";
800
801 # first parse the initial "["
802 for (;;) {
803 sysread $fh, my $buf, 65536
804 or die "read error: $!";
805 $json->incr_parse ($buf); # void context, so no parsing
806
807 # Exit the loop once we found and removed(!) the initial "[".
808 # In essence, we are (ab-)using the $json object as a simple scalar
809 # we append data to.
810 last if $json->incr_text =~ s/^ \s* \[ //x;
811 }
812
813 # now we have the skipped the initial "[", so continue
814 # parsing all the elements.
815 for (;;) {
816 # in this loop we read data until we got a single JSON object
817 for (;;) {
818 if (my $obj = $json->incr_parse) {
819 # do something with $obj
820 last;
821 }
822
823 # add more data
824 sysread $fh, my $buf, 65536
825 or die "read error: $!";
826 $json->incr_parse ($buf); # void context, so no parsing
827 }
828
829 # in this loop we read data until we either found and parsed the
830 # separating "," between elements, or the final "]"
831 for (;;) {
832 # first skip whitespace
833 $json->incr_text =~ s/^\s*//;
834
835 # if we find "]", we are done
836 if ($json->incr_text =~ s/^\]//) {
837 print "finished.\n";
838 exit;
839 }
840
841 # if we find ",", we can continue with the next element
842 if ($json->incr_text =~ s/^,//) {
843 last;
844 }
845
846 # if we find anything else, we have a parse error!
847 if (length $json->incr_text) {
848 die "parse error near ", $json->incr_text;
849 }
850
851 # else add more data
852 sysread $fh, my $buf, 65536
853 or die "read error: $!";
854 $json->incr_parse ($buf); # void context, so no parsing
855 }
856
857 This is a complex example, but most of the complexity comes from the
858 fact that we are trying to be correct (bear with me if I am wrong, I
859 never ran the above example :).
300 860
301MAPPING 861MAPPING
302 This section describes how JSON::XS maps Perl values to JSON values and 862 This section describes how JSON::XS maps Perl values to JSON values and
303 vice versa. These mappings are designed to "do the right thing" in most 863 vice versa. These mappings are designed to "do the right thing" in most
304 circumstances automatically, preserving round-tripping characteristics 864 circumstances automatically, preserving round-tripping characteristics
305 (what you put in comes out as something equivalent). 865 (what you put in comes out as something equivalent).
306 866
307 For the more enlightened: note that in the following descriptions, 867 For the more enlightened: note that in the following descriptions,
308 lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* 868 lowercase *perl* refers to the Perl interpreter, while uppercase *Perl*
309 refers to the abstract Perl language itself. 869 refers to the abstract Perl language itself.
310 870
311 JSON -> PERL 871 JSON -> PERL
312 object 872 object
313 A JSON object becomes a reference to a hash in Perl. No ordering of 873 A JSON object becomes a reference to a hash in Perl. No ordering of
314 object keys is preserved (JSON does not preserver object key 874 object keys is preserved (JSON does not preserve object key ordering
315 ordering itself). 875 itself).
316 876
317 array 877 array
318 A JSON array becomes a reference to an array in Perl. 878 A JSON array becomes a reference to an array in Perl.
319 879
320 string 880 string
321 A JSON string becomes a string scalar in Perl - Unicode codepoints 881 A JSON string becomes a string scalar in Perl - Unicode codepoints
322 in JSON are represented by the same codepoints in the Perl string, 882 in JSON are represented by the same codepoints in the Perl string,
323 so no manual decoding is necessary. 883 so no manual decoding is necessary.
324 884
325 number 885 number
326 A JSON number becomes either an integer or numeric (floating point) 886 A JSON number becomes either an integer, numeric (floating point) or
327 scalar in perl, depending on its range and any fractional parts. On 887 string scalar in perl, depending on its range and any fractional
328 the Perl level, there is no difference between those as Perl handles 888 parts. On the Perl level, there is no difference between those as
329 all the conversion details, but an integer may take slightly less 889 Perl handles all the conversion details, but an integer may take
330 memory and might represent more values exactly than (floating point) 890 slightly less memory and might represent more values exactly than
891 floating point numbers.
892
893 If the number consists of digits only, JSON::XS will try to
894 represent it as an integer value. If that fails, it will try to
895 represent it as a numeric (floating point) value if that is possible
896 without loss of precision. Otherwise it will preserve the number as
897 a string value (in which case you lose roundtripping ability, as the
898 JSON number will be re-encoded to a JSON string).
899
900 Numbers containing a fractional or exponential part will always be
901 represented as numeric (floating point) values, possibly at a loss
902 of precision (in which case you might lose perfect roundtripping
903 ability, but the JSON number will still be re-encoded as a JSON
331 numbers. 904 number).
905
906 Note that precision is not accuracy - binary floating point values
907 cannot represent most decimal fractions exactly, and when converting
908 from and to floating point, JSON::XS only guarantees precision up to
909 but not including the least significant bit.
332 910
333 true, false 911 true, false
334 These JSON atoms become 0, 1, respectively. Information is lost in 912 These JSON atoms become "Types::Serialiser::true" and
335 this process. Future versions might represent those values 913 "Types::Serialiser::false", respectively. They are overloaded to act
336 differently, but they will be guarenteed to act like these integers 914 almost exactly like the numbers 1 and 0. You can check whether a
337 would normally in Perl. 915 scalar is a JSON boolean by using the "Types::Serialiser::is_bool"
916 function (after "use Types::Serialier", of course).
338 917
339 null 918 null
340 A JSON null atom becomes "undef" in Perl. 919 A JSON null atom becomes "undef" in Perl.
920
921 shell-style comments ("# *text*")
922 As a nonstandard extension to the JSON syntax that is enabled by the
923 "relaxed" setting, shell-style comments are allowed. They can start
924 anywhere outside strings and go till the end of the line.
925
926 tagged values ("(*tag*)*value*").
927 Another nonstandard extension to the JSON syntax, enabled with the
928 "allow_tags" setting, are tagged values. In this implementation, the
929 *tag* must be a perl package/class name encoded as a JSON string,
930 and the *value* must be a JSON array encoding optional constructor
931 arguments.
932
933 See "OBJECT SERIALISATION", below, for details.
341 934
342 PERL -> JSON 935 PERL -> JSON
343 The mapping from Perl to JSON is slightly more difficult, as Perl is a 936 The mapping from Perl to JSON is slightly more difficult, as Perl is a
344 truly typeless language, so we can only guess which JSON type is meant 937 truly typeless language, so we can only guess which JSON type is meant
345 by a Perl value. 938 by a Perl value.
346 939
347 hash references 940 hash references
348 Perl hash references become JSON objects. As there is no inherent 941 Perl hash references become JSON objects. As there is no inherent
349 ordering in hash keys, they will usually be encoded in a 942 ordering in hash keys (or JSON objects), they will usually be
350 pseudo-random order that can change between runs of the same program 943 encoded in a pseudo-random order. JSON::XS can optionally sort the
351 but stays generally the same within a single run of a program. 944 hash keys (determined by the *canonical* flag), so the same
352 JSON::XS can optionally sort the hash keys (determined by the 945 datastructure will serialise to the same JSON text (given same
353 *canonical* flag), so the same datastructure will serialise to the 946 settings and version of JSON::XS), but this incurs a runtime
354 same JSON text (given same settings and version of JSON::XS), but 947 overhead and is only rarely useful, e.g. when you want to compare
355 this incurs a runtime overhead. 948 some JSON text against another for equality.
356 949
357 array references 950 array references
358 Perl array references become JSON arrays. 951 Perl array references become JSON arrays.
359 952
953 other references
954 Other unblessed references are generally not allowed and will cause
955 an exception to be thrown, except for references to the integers 0
956 and 1, which get turned into "false" and "true" atoms in JSON.
957
958 Since "JSON::XS" uses the boolean model from Types::Serialiser, you
959 can also "use Types::Serialiser" and then use
960 "Types::Serialiser::false" and "Types::Serialiser::true" to improve
961 readability.
962
963 use Types::Serialiser;
964 encode_json [\0, Types::Serialiser::true] # yields [false,true]
965
966 Types::Serialiser::true, Types::Serialiser::false
967 These special values from the Types::Serialiser module become JSON
968 true and JSON false values, respectively. You can also use "\1" and
969 "\0" directly if you want.
970
360 blessed objects 971 blessed objects
361 Blessed objects are not allowed. JSON::XS currently tries to encode 972 Blessed objects are not directly representable in JSON, but
362 their underlying representation (hash- or arrayref), but this 973 "JSON::XS" allows various ways of handling objects. See "OBJECT
363 behaviour might change in future versions. 974 SERIALISATION", below, for details.
364 975
365 simple scalars 976 simple scalars
366 Simple Perl scalars (any scalar that is not a reference) are the 977 Simple Perl scalars (any scalar that is not a reference) are the
367 most difficult objects to encode: JSON::XS will encode undefined 978 most difficult objects to encode: JSON::XS will encode undefined
368 scalars as JSON null value, scalars that have last been used in a 979 scalars as JSON "null" values, scalars that have last been used in a
369 string context before encoding as JSON strings and anything else as 980 string context before encoding as JSON strings, and anything else as
370 number value: 981 number value:
371 982
372 # dump as number 983 # dump as number
373 to_json [2] # yields [2] 984 encode_json [2] # yields [2]
374 to_json [-3.0e17] # yields [-3e+17] 985 encode_json [-3.0e17] # yields [-3e+17]
375 my $value = 5; to_json [$value] # yields [5] 986 my $value = 5; encode_json [$value] # yields [5]
376 987
377 # used as string, so dump as string 988 # used as string, so dump as string
378 print $value; 989 print $value;
379 to_json [$value] # yields ["5"] 990 encode_json [$value] # yields ["5"]
380 991
381 # undef becomes null 992 # undef becomes null
382 to_json [undef] # yields [null] 993 encode_json [undef] # yields [null]
383 994
384 You can force the type to be a string by stringifying it: 995 You can force the type to be a JSON string by stringifying it:
385 996
386 my $x = 3.1; # some variable containing a number 997 my $x = 3.1; # some variable containing a number
387 "$x"; # stringified 998 "$x"; # stringified
388 $x .= ""; # another, more awkward way to stringify 999 $x .= ""; # another, more awkward way to stringify
389 print $x; # perl does it for you, too, quite often 1000 print $x; # perl does it for you, too, quite often
390 1001
391 You can force the type to be a number by numifying it: 1002 You can force the type to be a JSON number by numifying it:
392 1003
393 my $x = "3"; # some variable containing a string 1004 my $x = "3"; # some variable containing a string
394 $x += 0; # numify it, ensuring it will be dumped as a number 1005 $x += 0; # numify it, ensuring it will be dumped as a number
395 $x *= 1; # same thing, the choise is yours. 1006 $x *= 1; # same thing, the choice is yours.
396 1007
397 You can not currently output JSON booleans or force the type in 1008 You can not currently force the type in other, less obscure, ways.
398 other, less obscure, ways. Tell me if you need this capability. 1009 Tell me if you need this capability (but don't forget to explain why
1010 it's needed :).
399 1011
400 circular data structures 1012 Note that numerical precision has the same meaning as under Perl (so
401 Those will be encoded until memory or stackspace runs out. 1013 binary to decimal conversion follows the same rules as in Perl,
1014 which can differ to other languages). Also, your perl interpreter
1015 might expose extensions to the floating point numbers of your
1016 platform, such as infinities or NaN's - these cannot be represented
1017 in JSON, and it is an error to pass those in.
402 1018
403COMPARISON 1019 OBJECT SERIALISATION
404 As already mentioned, this module was created because none of the 1020 As JSON cannot directly represent Perl objects, you have to choose
405 existing JSON modules could be made to work correctly. First I will 1021 between a pure JSON representation (without the ability to deserialise
406 describe the problems (or pleasures) I encountered with various existing 1022 the object automatically again), and a nonstandard extension to the JSON
407 JSON modules, followed by some benchmark values. JSON::XS was designed 1023 syntax, tagged values.
408 not to suffer from any of these problems or limitations.
409 1024
410 JSON 1.07 1025 SERIALISATION
411 Slow (but very portable, as it is written in pure Perl). 1026 What happens when "JSON::XS" encounters a Perl object depends on the
1027 "allow_blessed", "convert_blessed" and "allow_tags" settings, which are
1028 used in this order:
412 1029
413 Undocumented/buggy Unicode handling (how JSON handles unicode values 1030 1. "allow_tags" is enabled and the object has a "FREEZE" method.
414 is undocumented. One can get far by feeding it unicode strings and 1031 In this case, "JSON::XS" uses the Types::Serialiser object
415 doing en-/decoding oneself, but unicode escapes are not working 1032 serialisation protocol to create a tagged JSON value, using a
1033 nonstandard extension to the JSON syntax.
1034
1035 This works by invoking the "FREEZE" method on the object, with the
1036 first argument being the object to serialise, and the second
1037 argument being the constant string "JSON" to distinguish it from
1038 other serialisers.
1039
1040 The "FREEZE" method can return any number of values (i.e. zero or
1041 more). These values and the paclkage/classname of the object will
1042 then be encoded as a tagged JSON value in the following format:
1043
1044 ("classname")[FREEZE return values...]
1045
1046 e.g.:
1047
1048 ("URI")["http://www.google.com/"]
1049 ("MyDate")[2013,10,29]
1050 ("ImageData::JPEG")["Z3...VlCg=="]
1051
1052 For example, the hypothetical "My::Object" "FREEZE" method might use
1053 the objects "type" and "id" members to encode the object:
1054
1055 sub My::Object::FREEZE {
1056 my ($self, $serialiser) = @_;
1057
1058 ($self->{type}, $self->{id})
1059 }
1060
1061 2. "convert_blessed" is enabled and the object has a "TO_JSON" method.
1062 In this case, the "TO_JSON" method of the object is invoked in
1063 scalar context. It must return a single scalar that can be directly
1064 encoded into JSON. This scalar replaces the object in the JSON text.
1065
1066 For example, the following "TO_JSON" method will convert all URI
1067 objects to JSON strings when serialised. The fatc that these values
1068 originally were URI objects is lost.
1069
1070 sub URI::TO_JSON {
1071 my ($uri) = @_;
1072 $uri->as_string
1073 }
1074
1075 3. "allow_blessed" is enabled.
1076 The object will be serialised as a JSON null value.
1077
1078 4. none of the above
1079 If none of the settings are enabled or the respective methods are
1080 missing, "JSON::XS" throws an exception.
1081
1082 DESERIALISATION
1083 For deserialisation there are only two cases to consider: either
1084 nonstandard tagging was used, in which case "allow_tags" decides, or
1085 objects cannot be automatically be deserialised, in which case you can
1086 use postprocessing or the "filter_json_object" or
1087 "filter_json_single_key_object" callbacks to get some real objects our
1088 of your JSON.
1089
1090 This section only considers the tagged value case: I a tagged JSON
1091 object is encountered during decoding and "allow_tags" is disabled, a
1092 parse error will result (as if tagged values were not part of the
1093 grammar).
1094
1095 If "allow_tags" is enabled, "JSON::XS" will look up the "THAW" method of
1096 the package/classname used during serialisation (it will not attempt to
1097 load the package as a Perl module). If there is no such method, the
1098 decoding will fail with an error.
1099
1100 Otherwise, the "THAW" method is invoked with the classname as first
1101 argument, the constant string "JSON" as second argument, and all the
1102 values from the JSON array (the values originally returned by the
1103 "FREEZE" method) as remaining arguments.
1104
1105 The method must then return the object. While technically you can return
1106 any Perl scalar, you might have to enable the "enable_nonref" setting to
1107 make that work in all cases, so better return an actual blessed
1108 reference.
1109
1110 As an example, let's implement a "THAW" function that regenerates the
1111 "My::Object" from the "FREEZE" example earlier:
1112
1113 sub My::Object::THAW {
1114 my ($class, $serialiser, $type, $id) = @_;
1115
1116 $class->new (type => $type, id => $id)
1117 }
1118
1119ENCODING/CODESET FLAG NOTES
1120 The interested reader might have seen a number of flags that signify
1121 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
1122 some confusion on what these do, so here is a short comparison:
1123
1124 "utf8" controls whether the JSON text created by "encode" (and expected
1125 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
1126 control whether "encode" escapes character values outside their
1127 respective codeset range. Neither of these flags conflict with each
1128 other, although some combinations make less sense than others.
1129
1130 Care has been taken to make all flags symmetrical with respect to
1131 "encode" and "decode", that is, texts encoded with any combination of
1132 these flag values will be correctly decoded when the same flags are used
1133 - in general, if you use different flag settings while encoding vs. when
1134 decoding you likely have a bug somewhere.
1135
1136 Below comes a verbose discussion of these flags. Note that a "codeset"
1137 is simply an abstract set of character-codepoint pairs, while an
1138 encoding takes those codepoint numbers and *encodes* them, in our case
1139 into octets. Unicode is (among other things) a codeset, UTF-8 is an
1140 encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
1141 encodings at the same time, which can be confusing.
1142
1143 "utf8" flag disabled
1144 When "utf8" is disabled (the default), then "encode"/"decode"
1145 generate and expect Unicode strings, that is, characters with high
1146 ordinal Unicode values (> 255) will be encoded as such characters,
1147 and likewise such characters are decoded as-is, no changes to them
1148 will be done, except "(re-)interpreting" them as Unicode codepoints
1149 or Unicode characters, respectively (to Perl, these are the same
1150 thing in strings unless you do funny/weird/dumb stuff).
1151
1152 This is useful when you want to do the encoding yourself (e.g. when
1153 you want to have UTF-16 encoded JSON texts) or when some other layer
1154 does the encoding for you (for example, when printing to a terminal
1155 using a filehandle that transparently encodes to UTF-8 you certainly
1156 do NOT want to UTF-8 encode your data first and have Perl encode it
1157 another time).
1158
1159 "utf8" flag enabled
1160 If the "utf8"-flag is enabled, "encode"/"decode" will encode all
1161 characters using the corresponding UTF-8 multi-byte sequence, and
1162 will expect your input strings to be encoded as UTF-8, that is, no
1163 "character" of the input string must have any value > 255, as UTF-8
1164 does not allow that.
1165
1166 The "utf8" flag therefore switches between two modes: disabled means
1167 you will get a Unicode string in Perl, enabled means you get an
1168 UTF-8 encoded octet/binary string in Perl.
1169
1170 "latin1" or "ascii" flags enabled
1171 With "latin1" (or "ascii") enabled, "encode" will escape characters
1172 with ordinal values > 255 (> 127 with "ascii") and encode the
1173 remaining characters as specified by the "utf8" flag.
1174
1175 If "utf8" is disabled, then the result is also correctly encoded in
1176 those character sets (as both are proper subsets of Unicode, meaning
1177 that a Unicode string with all character values < 256 is the same
1178 thing as a ISO-8859-1 string, and a Unicode string with all
1179 character values < 128 is the same thing as an ASCII string in
416 properly). 1180 Perl).
417 1181
418 No roundtripping (strings get clobbered if they look like numbers, 1182 If "utf8" is enabled, you still get a correct UTF-8-encoded string,
419 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that 1183 regardless of these flags, just some more characters will be escaped
420 will decode into the number 2. 1184 using "\uXXXX" then before.
421 1185
422 JSON::PC 0.01 1186 Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
423 Very fast. 1187 encoding, while ASCII-encoded strings are. That is because the
1188 ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
1189 *codeset* being a subset of Unicode), while ASCII is.
424 1190
425 Undocumented/buggy Unicode handling. 1191 Surprisingly, "decode" will ignore these flags and so treat all
1192 input values as governed by the "utf8" flag. If it is disabled, this
1193 allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
1194 strict subsets of Unicode. If it is enabled, you can correctly
1195 decode UTF-8 encoded strings.
426 1196
427 No roundtripping. 1197 So neither "latin1" nor "ascii" are incompatible with the "utf8"
1198 flag - they only govern when the JSON output engine escapes a
1199 character or not.
428 1200
429 Has problems handling many Perl values (e.g. regex results and other 1201 The main use for "latin1" is to relatively efficiently store binary
430 magic values will make it croak). 1202 data as JSON, at the expense of breaking compatibility with most
1203 JSON decoders.
431 1204
432 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 1205 The main use for "ascii" is to force the output to not contain
433 which is not a valid JSON text. 1206 characters with values > 127, which means you can interpret the
1207 resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
1208 any character set and 8-bit-encoding, and still get the same data
1209 structure back. This is useful when your channel for JSON transfer
1210 is not 8-bit clean or the encoding might be mangled in between (e.g.
1211 in mail), and works because ASCII is a proper subset of most 8-bit
1212 and multibyte encodings in use in the world.
434 1213
435 Unmaintained (maintainer unresponsive for many months, bugs are not 1214 JSON and ECMAscript
436 getting fixed). 1215 JSON syntax is based on how literals are represented in javascript (the
1216 not-standardised predecessor of ECMAscript) which is presumably why it
1217 is called "JavaScript Object Notation".
437 1218
438 JSON::Syck 0.21 1219 However, JSON is not a subset (and also not a superset of course) of
439 Very buggy (often crashes). 1220 ECMAscript (the standard) or javascript (whatever browsers actually
1221 implement).
440 1222
441 Very inflexible (no human-readable format supported, format pretty 1223 If you want to use javascript's "eval" function to "parse" JSON, you
442 much undocumented. I need at least a format for easy reading by 1224 might run into parse errors for valid JSON texts, or the resulting data
443 humans and a single-line compact format for use in a protocol, and 1225 structure might not be queryable:
444 preferably a way to generate ASCII-only JSON texts).
445 1226
446 Completely broken (and confusingly documented) Unicode handling 1227 One of the problems is that U+2028 and U+2029 are valid characters
447 (unicode escapes are not working properly, you need to set 1228 inside JSON strings, but are not allowed in ECMAscript string literals,
448 ImplicitUnicode to *different* values on en- and decoding to get 1229 so the following Perl fragment will not output something that can be
449 symmetric behaviour). 1230 guaranteed to be parsable by javascript's "eval":
450 1231
451 No roundtripping (simple cases work, but this depends on wether the 1232 use JSON::XS;
452 scalar value was used in a numeric context or not).
453 1233
454 Dumping hashes may skip hash values depending on iterator state. 1234 print encode_json [chr 0x2028];
455 1235
456 Unmaintained (maintainer unresponsive for many months, bugs are not 1236 The right fix for this is to use a proper JSON parser in your javascript
457 getting fixed). 1237 programs, and not rely on "eval" (see for example Douglas Crockford's
1238 json2.js parser).
458 1239
459 Does not check input for validity (i.e. will accept non-JSON input 1240 If this is not an option, you can, as a stop-gap measure, simply encode
460 and return "something" instead of raising an exception. This is a 1241 to ASCII-only JSON:
461 security issue: imagine two banks transfering money between each
462 other using JSON. One bank might parse a given non-JSON request and
463 deduct money, while the other might reject the transaction with a
464 syntax error. While a good protocol will at least recover, that is
465 extra unnecessary work and the transaction will still not succeed).
466 1242
467 JSON::DWIW 0.04 1243 use JSON::XS;
468 Very fast. Very natural. Very nice.
469 1244
470 Undocumented unicode handling (but the best of the pack. Unicode 1245 print JSON::XS->new->ascii->encode ([chr 0x2028]);
471 escapes still don't get parsed properly).
472 1246
473 Very inflexible. 1247 Note that this will enlarge the resulting JSON text quite a bit if you
1248 have many non-ASCII characters. You might be tempted to run some regexes
1249 to only escape U+2028 and U+2029, e.g.:
474 1250
475 No roundtripping. 1251 # DO NOT USE THIS!
1252 my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
1253 $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
1254 $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
1255 print $json;
476 1256
477 Does not generate valid JSON texts (key strings are often unquoted, 1257 Note that *this is a bad idea*: the above only works for U+2028 and
478 empty keys result in nothing being output) 1258 U+2029 and thus only for fully ECMAscript-compliant parsers. Many
1259 existing javascript implementations, however, have issues with other
1260 characters as well - using "eval" naively simply *will* cause problems.
479 1261
480 Does not check input for validity. 1262 Another problem is that some javascript implementations reserve some
1263 property names for their own purposes (which probably makes them
1264 non-ECMAscript-compliant). For example, Iceweasel reserves the
1265 "__proto__" property name for its own purposes.
1266
1267 If that is a problem, you could parse try to filter the resulting JSON
1268 output for these property strings, e.g.:
1269
1270 $json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
1271
1272 This works because "__proto__" is not valid outside of strings, so every
1273 occurrence of ""__proto__"\s*:" must be a string used as property name.
1274
1275 If you know of other incompatibilities, please let me know.
1276
1277 JSON and YAML
1278 You often hear that JSON is a subset of YAML. This is, however, a mass
1279 hysteria(*) and very far from the truth (as of the time of this
1280 writing), so let me state it clearly: *in general, there is no way to
1281 configure JSON::XS to output a data structure as valid YAML* that works
1282 in all cases.
1283
1284 If you really must use JSON::XS to generate YAML, you should use this
1285 algorithm (subject to change in future versions):
1286
1287 my $to_yaml = JSON::XS->new->utf8->space_after (1);
1288 my $yaml = $to_yaml->encode ($ref) . "\n";
1289
1290 This will *usually* generate JSON texts that also parse as valid YAML.
1291 Please note that YAML has hardcoded limits on (simple) object key
1292 lengths that JSON doesn't have and also has different and incompatible
1293 unicode character escape syntax, so you should make sure that your hash
1294 keys are noticeably shorter than the 1024 "stream characters" YAML
1295 allows and that you do not have characters with codepoint values outside
1296 the Unicode BMP (basic multilingual page). YAML also does not allow "\/"
1297 sequences in strings (which JSON::XS does not *currently* generate, but
1298 other JSON generators might).
1299
1300 There might be other incompatibilities that I am not aware of (or the
1301 YAML specification has been changed yet again - it does so quite often).
1302 In general you should not try to generate YAML with a JSON generator or
1303 vice versa, or try to parse JSON with a YAML parser or vice versa:
1304 chances are high that you will run into severe interoperability problems
1305 when you least expect it.
1306
1307 (*) I have been pressured multiple times by Brian Ingerson (one of the
1308 authors of the YAML specification) to remove this paragraph, despite
1309 him acknowledging that the actual incompatibilities exist. As I was
1310 personally bitten by this "JSON is YAML" lie, I refused and said I
1311 will continue to educate people about these issues, so others do not
1312 run into the same problem again and again. After this, Brian called
1313 me a (quote)*complete and worthless idiot*(unquote).
1314
1315 In my opinion, instead of pressuring and insulting people who
1316 actually clarify issues with YAML and the wrong statements of some
1317 of its proponents, I would kindly suggest reading the JSON spec
1318 (which is not that difficult or long) and finally make YAML
1319 compatible to it, and educating users about the changes, instead of
1320 spreading lies about the real compatibility for many *years* and
1321 trying to silence people who point out that it isn't true.
1322
1323 Addendum/2009: the YAML 1.2 spec is still incompatible with JSON,
1324 even though the incompatibilities have been documented (and are
1325 known to Brian) for many years and the spec makes explicit claims
1326 that YAML is a superset of JSON. It would be so easy to fix, but
1327 apparently, bullying people and corrupting userdata is so much
1328 easier.
481 1329
482 SPEED 1330 SPEED
483 It seems that JSON::XS is surprisingly fast, as shown in the following 1331 It seems that JSON::XS is surprisingly fast, as shown in the following
484 tables. They have been generated with the help of the "eg/bench" program 1332 tables. They have been generated with the help of the "eg/bench" program
485 in the JSON::XS distribution, to make it easy to compare on your own 1333 in the JSON::XS distribution, to make it easy to compare on your own
486 system. 1334 system.
487 1335
488 First comes a comparison between various modules using a very short JSON 1336 First comes a comparison between various modules using a very short
489 string: 1337 single-line JSON string (also available at
1338 <http://dist.schmorp.de/misc/json/short.json>).
490 1339
491 {"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null} 1340 {"method": "handleMessage", "params": ["user1",
1341 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1342 1, 0]}
492 1343
493 It shows the number of encodes/decodes per second (JSON::XS uses the 1344 It shows the number of encodes/decodes per second (JSON::XS uses the
494 functional interface, while JSON::XS/2 uses the OO interface with 1345 functional interface, while JSON::XS/2 uses the OO interface with
495 pretty-printing and hashkey sorting enabled). Higher is better: 1346 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink.
1347 JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses
1348 the from_json method). Higher is better:
496 1349
497 module | encode | decode | 1350 module | encode | decode |
498 -----------|------------|------------| 1351 --------------|------------|------------|
499 JSON | 11488.516 | 7823.035 | 1352 JSON::DWIW/DS | 86302.551 | 102300.098 |
500 JSON::DWIW | 94708.054 | 129094.260 | 1353 JSON::DWIW/FJ | 86302.551 | 75983.768 |
501 JSON::PC | 63884.157 | 128528.212 | 1354 JSON::PP | 15827.562 | 6638.658 |
502 JSON::Syck | 34898.677 | 42096.911 | 1355 JSON::Syck | 63358.066 | 47662.545 |
503 JSON::XS | 654027.064 | 396423.669 | 1356 JSON::XS | 511500.488 | 511500.488 |
504 JSON::XS/2 | 371564.190 | 371725.613 | 1357 JSON::XS/2 | 291271.111 | 388361.481 |
1358 JSON::XS/3 | 361577.931 | 361577.931 |
1359 Storable | 66788.280 | 265462.278 |
505 -----------+------------+------------+ 1360 --------------+------------+------------+
506 1361
507 That is, JSON::XS is more than six times faster than JSON::DWIW on 1362 That is, JSON::XS is almost six times faster than JSON::DWIW on
508 encoding, more than three times faster on decoding, and about thirty 1363 encoding, about five times faster on decoding, and over thirty to
509 times faster than JSON, even with pretty-printing and key sorting. 1364 seventy times faster than JSON's pure perl implementation. It also
1365 compares favourably to Storable for small amounts of data.
510 1366
511 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1367 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
512 search API (http://nanoref.com/yahooapis/mgPdGg): 1368 search API (<http://dist.schmorp.de/misc/json/long.json>).
513 1369
514 module | encode | decode | 1370 module | encode | decode |
515 -----------|------------|------------| 1371 --------------|------------|------------|
516 JSON | 273.023 | 44.674 | 1372 JSON::DWIW/DS | 1647.927 | 2673.916 |
517 JSON::DWIW | 1089.383 | 1145.704 | 1373 JSON::DWIW/FJ | 1630.249 | 2596.128 |
518 JSON::PC | 3097.419 | 2393.921 | 1374 JSON::PP | 400.640 | 62.311 |
519 JSON::Syck | 514.060 | 843.053 | 1375 JSON::Syck | 1481.040 | 1524.869 |
520 JSON::XS | 6479.668 | 3636.364 | 1376 JSON::XS | 20661.596 | 9541.183 |
521 JSON::XS/2 | 3774.221 | 3599.124 | 1377 JSON::XS/2 | 10683.403 | 9416.938 |
1378 JSON::XS/3 | 20661.596 | 9400.054 |
1379 Storable | 19765.806 | 10000.725 |
522 -----------+------------+------------+ 1380 --------------+------------+------------+
523 1381
524 Again, JSON::XS leads by far. 1382 Again, JSON::XS leads by far (except for Storable which non-surprisingly
1383 decodes a bit faster).
525 1384
526 On large strings containing lots of high unicode characters, some 1385 On large strings containing lots of high Unicode characters, some
527 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the 1386 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
528 result will be broken due to missing (or wrong) unicode handling. Others 1387 result will be broken due to missing (or wrong) Unicode handling. Others
529 refuse to decode or encode properly, so it was impossible to prepare a 1388 refuse to decode or encode properly, so it was impossible to prepare a
530 fair comparison table for that case. 1389 fair comparison table for that case.
531 1390
532SECURITY CONSIDERATIONS 1391SECURITY CONSIDERATIONS
533 When you are using JSON in a protocol, talking to untrusted potentially 1392 When you are using JSON in a protocol, talking to untrusted potentially
… …
537 have any buffer overflows. Obviously, this module should ensure that and 1396 have any buffer overflows. Obviously, this module should ensure that and
538 I am trying hard on making that true, but you never know. 1397 I am trying hard on making that true, but you never know.
539 1398
540 Second, you need to avoid resource-starving attacks. That means you 1399 Second, you need to avoid resource-starving attacks. That means you
541 should limit the size of JSON texts you accept, or make sure then when 1400 should limit the size of JSON texts you accept, or make sure then when
542 your resources run out, thats just fine (e.g. by using a separate 1401 your resources run out, that's just fine (e.g. by using a separate
543 process that can crash safely). The size of a JSON text in octets or 1402 process that can crash safely). The size of a JSON text in octets or
544 characters is usually a good indication of the size of the resources 1403 characters is usually a good indication of the size of the resources
545 required to decode it into a Perl structure. 1404 required to decode it into a Perl structure. While JSON::XS can check
1405 the size of the JSON text, it might be too late when you already have it
1406 in memory, so you might want to check the size before you accept the
1407 string.
546 1408
547 Third, JSON::XS recurses using the C stack when decoding objects and 1409 Third, JSON::XS recurses using the C stack when decoding objects and
548 arrays. The C stack is a limited resource: for instance, on my amd64 1410 arrays. The C stack is a limited resource: for instance, on my amd64
549 machine with 8MB of stack size I can decode around 180k nested arrays 1411 machine with 8MB of stack size I can decode around 180k nested arrays
550 but only 14k nested JSON objects. If that is exceeded, the program 1412 but only 14k nested JSON objects (due to perl itself recursing deeply on
1413 croak to free the temporary). If that is exceeded, the program crashes.
551 crashes. Thats why the default nesting limit is set to 8192. If your 1414 To be conservative, the default nesting limit is set to 512. If your
552 process has a smaller stack, you should adjust this setting accordingly 1415 process has a smaller stack, you should adjust this setting accordingly
553 with the "max_depth" method. 1416 with the "max_depth" method.
554 1417
555 And last but least, something else could bomb you that I forgot to think 1418 Something else could bomb you, too, that I forgot to think of. In that
556 of. In that case, you get to keep the pieces. I am alway sopen for 1419 case, you get to keep the pieces. I am always open for hints, though...
557 hints, though... 1420
1421 Also keep in mind that JSON::XS might leak contents of your Perl data
1422 structures in its error messages, so when you serialise sensitive
1423 information you might want to make sure that exceptions thrown by
1424 JSON::XS will not end up in front of untrusted eyes.
1425
1426 If you are using JSON::XS to return packets to consumption by JavaScript
1427 scripts in a browser you should have a look at
1428 <http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/>
1429 to see whether you are vulnerable to some common attack vectors (which
1430 really are browser design bugs, but it is still you who will have to
1431 deal with it, as major browser developers care only for features, not
1432 about getting security right).
1433
1434INTEROPERABILITY WITH OTHER MODULES
1435 "JSON::XS" uses the Types::Serialiser module to provide boolean
1436 constants. That means that the JSON true and false values will be
1437 comaptible to true and false values of iother modules that do the same,
1438 such as JSON::PP and CBOR::XS.
1439
1440THREADS
1441 This module is *not* guaranteed to be thread safe and there are no plans
1442 to change this until Perl gets thread support (as opposed to the
1443 horribly slow so-called "threads" which are simply slow and bloated
1444 process simulations - use fork, it's *much* faster, cheaper, better).
1445
1446 (It might actually work, but you have been warned).
1447
1448THE PERILS OF SETLOCALE
1449 Sometimes people avoid the Perl locale support and directly call the
1450 system's setlocale function with "LC_ALL".
1451
1452 This breaks both perl and modules such as JSON::XS, as stringification
1453 of numbers no longer works correctly (e.g. "$x = 0.1; print "$x"+1"
1454 might print 1, and JSON::XS might output illegal JSON as JSON::XS relies
1455 on perl to stringify numbers).
1456
1457 The solution is simple: don't call "setlocale", or use it for only those
1458 categories you need, such as "LC_MESSAGES" or "LC_CTYPE".
1459
1460 If you need "LC_NUMERIC", you should enable it only around the code that
1461 actually needs it (avoiding stringification of numbers), and restore it
1462 afterwards.
558 1463
559BUGS 1464BUGS
560 While the goal of this module is to be correct, that unfortunately does 1465 While the goal of this module is to be correct, that unfortunately does
561 not mean its bug-free, only that I think its design is bug-free. It is 1466 not mean it's bug-free, only that I think its design is bug-free. If you
562 still relatively early in its development. If you keep reporting bugs
563 they will be fixed swiftly, though. 1467 keep reporting bugs they will be fixed swiftly, though.
1468
1469 Please refrain from using rt.cpan.org or any other bug reporting
1470 service. I put the contact address into my modules for a reason.
1471
1472SEE ALSO
1473 The json_xs command line utility for quick experiments.
564 1474
565AUTHOR 1475AUTHOR
566 Marc Lehmann <schmorp@schmorp.de> 1476 Marc Lehmann <schmorp@schmorp.de>
567 http://home.schmorp.de/ 1477 http://home.schmorp.de/
568 1478

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