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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 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 シリアライザ/デシリアライザ
6 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) 5 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
7 6
8SYNOPSIS 7SYNOPSIS
9 use JSON::XS; 8 use JSON::XS;
10 9
11 # exported functions, they croak on error 10 # exported functions, they croak on error
12 # and expect/generate UTF-8 11 # and expect/generate UTF-8
13 12
14 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 13 $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
15 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 14 $perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
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);
… …
33 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*.
34 To reach the latter goal it was written in C. 33 To reach the latter goal it was written in C.
35 34
36 Beginning with version 2.0 of the JSON module, when both JSON and 35 Beginning with version 2.0 of the JSON module, when both JSON and
37 JSON::XS are installed, then JSON will fall back on JSON::XS (this can 36 JSON::XS are installed, then JSON will fall back on JSON::XS (this can
38 be overriden) with no overhead due to emulation (by inheritign 37 be overridden) with no overhead due to emulation (by inheriting
39 constructor and methods). If JSON::XS is not available, it will fall 38 constructor and methods). If JSON::XS is not available, it will fall
40 back to the compatible JSON::PP module as backend, so using JSON instead 39 back to the compatible JSON::PP module as backend, so using JSON instead
41 of JSON::XS gives you a portable JSON API that can be fast when you need 40 of JSON::XS gives you a portable JSON API that can be fast when you need
42 and doesn't require a C compiler when that is a problem. 41 it and doesn't require a C compiler when that is a problem.
43 42
44 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
45 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
46 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
47 cases their maintainers are unresponsive, gone missing, or not listening 46 cases their maintainers are unresponsive, gone missing, or not listening
48 to bug reports for other reasons. 47 to bug reports for other reasons.
49 48
50 See COMPARISON, below, for a comparison to some other JSON modules.
51
52 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
53 vice versa. 50 vice versa.
54 51
55 FEATURES 52 FEATURES
56 * correct Unicode handling 53 * correct Unicode handling
54
57 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
58 when it does so. 56 does so, and even documents what "correct" means.
59 57
60 * round-trip integrity 58 * round-trip integrity
59
61 When you serialise a perl data structure using only datatypes 60 When you serialise a perl data structure using only data types
62 supported by JSON, the deserialised data structure is identical on 61 supported by JSON and Perl, the deserialised data structure is
63 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
64 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.
65 66
66 * strict checking of JSON correctness 67 * strict checking of JSON correctness
68
67 There is no guessing, no generating of illegal JSON texts by 69 There is no guessing, no generating of illegal JSON texts by
68 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
69 is a security feature). 71 is a security feature).
70 72
71 * fast 73 * fast
72 Compared to other JSON modules, this module compares favourably in
73 terms of speed, too.
74 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
75 * simple to use 79 * simple to use
80
76 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
77 interface. 82 object oriented interface.
78 83
79 * reasonably versatile output formats 84 * reasonably versatile output formats
85
80 You can choose between the most compact guaranteed single-line 86 You can choose between the most compact guaranteed-single-line
81 format possible (nice for simple line-based protocols), a pure-ascii 87 format possible (nice for simple line-based protocols), a pure-ASCII
82 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
83 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
84 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
85 whatever way you like. 91 whatever way you like.
86 92
87FUNCTIONAL INTERFACE 93FUNCTIONAL INTERFACE
88 The following convenience methods are provided by this module. They are 94 The following convenience methods are provided by this module. They are
89 exported by default: 95 exported by default:
90 96
91 $json_text = to_json $perl_scalar 97 $json_text = encode_json $perl_scalar
92 Converts the given Perl data structure to a UTF-8 encoded, binary 98 Converts the given Perl data structure to a UTF-8 encoded, binary
93 string (that is, the string contains octets only). Croaks on error. 99 string (that is, the string contains octets only). Croaks on error.
94 100
95 This function call is functionally identical to: 101 This function call is functionally identical to:
96 102
97 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 103 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
98 104
99 except being faster. 105 Except being faster.
100 106
101 $perl_scalar = from_json $json_text 107 $perl_scalar = decode_json $json_text
102 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
103 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
104 resulting reference. Croaks on error. 110 resulting reference. Croaks on error.
105 111
106 This function call is functionally identical to: 112 This function call is functionally identical to:
107 113
108 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 114 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
109 115
110 except being faster. 116 Except being faster.
111
112 $is_boolean = JSON::XS::is_bool $scalar
113 Returns true if the passed scalar represents either JSON::XS::true
114 or JSON::XS::false, two constants that act like 1 and 0,
115 respectively and are used to represent JSON "true" and "false"
116 values in Perl.
117
118 See MAPPING, below, for more information on how JSON values are
119 mapped to Perl.
120 117
121A FEW NOTES ON UNICODE AND PERL 118A FEW NOTES ON UNICODE AND PERL
122 Since this often leads to confusion, here are a few very clear words on 119 Since this often leads to confusion, here are a few very clear words on
123 how Unicode works in Perl, modulo bugs. 120 how Unicode works in Perl, modulo bugs.
124 121
125 1. Perl strings can store characters with ordinal values > 255. 122 1. Perl strings can store characters with ordinal values > 255.
126 This enables you to store Unicode characters as single characters in 123 This enables you to store Unicode characters as single characters in
127 a Perl string - very natural. 124 a Perl string - very natural.
128 125
129 2. Perl does *not* associate an encoding with your strings. 126 2. Perl does *not* associate an encoding with your strings.
130 Unless you force it to, e.g. when matching it against a regex, or 127 ... until you force it to, e.g. when matching it against a regex, or
131 printing the scalar to a file, in which case Perl either interprets 128 printing the scalar to a file, in which case Perl either interprets
132 your string as locale-encoded text, octets/binary, or as Unicode, 129 your string as locale-encoded text, octets/binary, or as Unicode,
133 depending on various settings. In no case is an encoding stored 130 depending on various settings. In no case is an encoding stored
134 together with your data, it is *use* that decides encoding, not any 131 together with your data, it is *use* that decides encoding, not any
135 magical metadata. 132 magical meta data.
136 133
137 3. The internal utf-8 flag has no meaning with regards to the encoding 134 3. The internal utf-8 flag has no meaning with regards to the encoding
138 of your string. 135 of your string.
139 Just ignore that flag unless you debug a Perl bug, a module written 136 Just ignore that flag unless you debug a Perl bug, a module written
140 in XS or want to dive into the internals of perl. Otherwise it will 137 in XS or want to dive into the internals of perl. Otherwise it will
… …
145 142
146 If you didn't know about that flag, just the better, pretend it 143 If you didn't know about that flag, just the better, pretend it
147 doesn't exist. 144 doesn't exist.
148 145
149 4. A "Unicode String" is simply a string where each character can be 146 4. A "Unicode String" is simply a string where each character can be
150 validly interpreted as a Unicode codepoint. 147 validly interpreted as a Unicode code point.
151 If you have UTF-8 encoded data, it is no longer a Unicode string, 148 If you have UTF-8 encoded data, it is no longer a Unicode string,
152 but a Unicode string encoded in UTF-8, giving you a binary string. 149 but a Unicode string encoded in UTF-8, giving you a binary string.
153 150
154 5. A string containing "high" (> 255) character values is *not* a UTF-8 151 5. A string containing "high" (> 255) character values is *not* a UTF-8
155 string. 152 string.
… …
185 182
186 If $enable is false, then the "encode" method will not escape 183 If $enable is false, then the "encode" method will not escape
187 Unicode characters unless required by the JSON syntax or other 184 Unicode characters unless required by the JSON syntax or other
188 flags. This results in a faster and more compact format. 185 flags. This results in a faster and more compact format.
189 186
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 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 191 transmitted over a 7-bit channel, as the encoded JSON texts will not
192 contain any 8 bit characters. 192 contain any 8 bit characters.
193 193
194 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 194 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
… …
205 superset of latin1. 205 superset of latin1.
206 206
207 If $enable is false, then the "encode" method will not escape 207 If $enable is false, then the "encode" method will not escape
208 Unicode characters unless required by the JSON syntax or other 208 Unicode characters unless required by the JSON syntax or other
209 flags. 209 flags.
210
211 See also the section *ENCODING/CODESET FLAG NOTES* later in this
212 document.
210 213
211 The main use for this flag is efficiently encoding binary data as 214 The main use for this flag is efficiently encoding binary data as
212 JSON text, as most octets will not be escaped, resulting in a 215 JSON text, as most octets will not be escaped, resulting in a
213 smaller encoded size. The disadvantage is that the resulting JSON 216 smaller encoded size. The disadvantage is that the resulting JSON
214 text is encoded in latin1 (and must correctly be treated as such 217 text is encoded in latin1 (and must correctly be treated as such
… …
234 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
235 string as a (non-encoded) Unicode string, while "decode" expects 238 string as a (non-encoded) Unicode string, while "decode" expects
236 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
237 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.
238 241
242 See also the section *ENCODING/CODESET FLAG NOTES* later in this
243 document.
244
239 Example, output UTF-16BE-encoded JSON: 245 Example, output UTF-16BE-encoded JSON:
240 246
241 use Encode; 247 use Encode;
242 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); 248 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
243 249
… …
318 If $enable is false (the default), then "decode" will only accept 324 If $enable is false (the default), then "decode" will only accept
319 valid JSON texts. 325 valid JSON texts.
320 326
321 Currently accepted extensions are: 327 Currently accepted extensions are:
322 328
323 * list items can have an end-comma 329 * list items can have an end-comma
330
324 JSON *separates* array elements and key-value pairs with commas. 331 JSON *separates* array elements and key-value pairs with commas.
325 This can be annoying if you write JSON texts manually and want 332 This can be annoying if you write JSON texts manually and want
326 to be able to quickly append elements, so this extension accepts 333 to be able to quickly append elements, so this extension accepts
327 comma at the end of such items not just between them: 334 comma at the end of such items not just between them:
328 335
… …
333 { 340 {
334 "k1": "v1", 341 "k1": "v1",
335 "k2": "v2", <- this comma not normally allowed 342 "k2": "v2", <- this comma not normally allowed
336 } 343 }
337 344
338 * shell-style '#'-comments 345 * shell-style '#'-comments
346
339 Whenever JSON allows whitespace, shell-style comments are 347 Whenever JSON allows whitespace, shell-style comments are
340 additionally allowed. They are terminated by the first 348 additionally allowed. They are terminated by the first
341 carriage-return or line-feed character, after which more 349 carriage-return or line-feed character, after which more
342 white-space and comments are allowed. 350 white-space and comments are allowed.
343 351
344 [ 352 [
345 1, # this comment not allowed in JSON 353 1, # this comment not allowed in JSON
346 # neither this one... 354 # neither this one...
355 ]
356
357 * literal ASCII TAB characters in strings
358
359 Literal ASCII TAB characters are now allowed in strings (and
360 treated as "\t").
361
362 [
363 "Hello\tWorld",
364 "Hello<TAB>World", # literal <TAB> would not normally be allowed
347 ] 365 ]
348 366
349 $json = $json->canonical ([$enable]) 367 $json = $json->canonical ([$enable])
350 $enabled = $json->get_canonical 368 $enabled = $json->get_canonical
351 If $enable is true (or missing), then the "encode" method will 369 If $enable is true (or missing), then the "encode" method will
352 output JSON objects by sorting their keys. This is adding a 370 output JSON objects by sorting their keys. This is adding a
353 comparatively high overhead. 371 comparatively high overhead.
354 372
355 If $enable is false, then the "encode" method will output key-value 373 If $enable is false, then the "encode" method will output key-value
356 pairs in the order Perl stores them (which will likely change 374 pairs in the order Perl stores them (which will likely change
357 between runs of the same script). 375 between runs of the same script, and can change even within the same
376 run from 5.18 onwards).
358 377
359 This option is useful if you want the same data structure to be 378 This option is useful if you want the same data structure to be
360 encoded as the same JSON text (given the same overall settings). If 379 encoded as the same JSON text (given the same overall settings). If
361 it is disabled, the same hash might be encoded differently even if 380 it is disabled, the same hash might be encoded differently even if
362 contains the same data, as key-value pairs have no inherent ordering 381 contains the same data, as key-value pairs have no inherent ordering
363 in Perl. 382 in Perl.
364 383
365 This setting has no effect when decoding JSON texts. 384 This setting has no effect when decoding JSON texts.
385
386 This setting has currently no effect on tied hashes.
366 387
367 $json = $json->allow_nonref ([$enable]) 388 $json = $json->allow_nonref ([$enable])
368 $enabled = $json->get_allow_nonref 389 $enabled = $json->get_allow_nonref
369 If $enable is true (or missing), then the "encode" method can 390 If $enable is true (or missing), then the "encode" method can
370 convert a non-reference into its corresponding string, number or 391 convert a non-reference into its corresponding string, number or
… …
380 "allow_nonref", resulting in an invalid JSON text: 401 "allow_nonref", resulting in an invalid JSON text:
381 402
382 JSON::XS->new->allow_nonref->encode ("Hello, World!") 403 JSON::XS->new->allow_nonref->encode ("Hello, World!")
383 => "Hello, World!" 404 => "Hello, World!"
384 405
406 $json = $json->allow_unknown ([$enable])
407 $enabled = $json->get_allow_unknown
408 If $enable is true (or missing), then "encode" will *not* throw an
409 exception when it encounters values it cannot represent in JSON (for
410 example, filehandles) but instead will encode a JSON "null" value.
411 Note that blessed objects are not included here and are handled
412 separately by c<allow_nonref>.
413
414 If $enable is false (the default), then "encode" will throw an
415 exception when it encounters anything it cannot encode as JSON.
416
417 This option does not affect "decode" in any way, and it is
418 recommended to leave it off unless you know your communications
419 partner.
420
385 $json = $json->allow_blessed ([$enable]) 421 $json = $json->allow_blessed ([$enable])
386 $enabled = $json->get_allow_blessed 422 $enabled = $json->get_allow_blessed
423 See "OBJECT SERIALISATION" for details.
424
387 If $enable is true (or missing), then the "encode" method will not 425 If $enable is true (or missing), then the "encode" method will not
388 barf when it encounters a blessed reference. Instead, the value of 426 barf when it encounters a blessed reference that it cannot convert
389 the convert_blessed option will decide whether "null" 427 otherwise. Instead, a JSON "null" value is encoded instead of the
390 ("convert_blessed" disabled or no "TO_JSON" method found) or a 428 object.
391 representation of the object ("convert_blessed" enabled and
392 "TO_JSON" method found) is being encoded. Has no effect on "decode".
393 429
394 If $enable is false (the default), then "encode" will throw an 430 If $enable is false (the default), then "encode" will throw an
395 exception when it encounters a blessed object. 431 exception when it encounters a blessed object that it cannot convert
432 otherwise.
433
434 This setting has no effect on "decode".
396 435
397 $json = $json->convert_blessed ([$enable]) 436 $json = $json->convert_blessed ([$enable])
398 $enabled = $json->get_convert_blessed 437 $enabled = $json->get_convert_blessed
438 See "OBJECT SERIALISATION" for details.
439
399 If $enable is true (or missing), then "encode", upon encountering a 440 If $enable is true (or missing), then "encode", upon encountering a
400 blessed object, will check for the availability of the "TO_JSON" 441 blessed object, will check for the availability of the "TO_JSON"
401 method on the object's class. If found, it will be called in scalar 442 method on the object's class. If found, it will be called in scalar
402 context and the resulting scalar will be encoded instead of the 443 context and the resulting scalar will be encoded instead of the
403 object. If no "TO_JSON" method is found, the value of 444 object.
404 "allow_blessed" will decide what to do.
405 445
406 The "TO_JSON" method may safely call die if it wants. If "TO_JSON" 446 The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
407 returns other blessed objects, those will be handled in the same 447 returns other blessed objects, those will be handled in the same
408 way. "TO_JSON" must take care of not causing an endless recursion 448 way. "TO_JSON" must take care of not causing an endless recursion
409 cycle (== crash) in this case. The name of "TO_JSON" was chosen 449 cycle (== crash) in this case. The name of "TO_JSON" was chosen
410 because other methods called by the Perl core (== not by the user of 450 because other methods called by the Perl core (== not by the user of
411 the object) are usually in upper case letters and to avoid 451 the object) are usually in upper case letters and to avoid
412 collisions with the "to_json" function. 452 collisions with any "to_json" function or method.
413 453
414 This setting does not yet influence "decode" in any way, but in the 454 If $enable is false (the default), then "encode" will not consider
415 future, global hooks might get installed that influence "decode" and 455 this type of conversion.
416 are enabled by this setting.
417 456
418 If $enable is false, then the "allow_blessed" setting will decide 457 This setting has no effect on "decode".
419 what to do when a blessed object is found. 458
459 $json = $json->allow_tags ([$enable])
460 $enabled = $json->allow_tags
461 See "OBJECT SERIALISATION" for details.
462
463 If $enable is true (or missing), then "encode", upon encountering a
464 blessed object, will check for the availability of the "FREEZE"
465 method on the object's class. If found, it will be used to serialise
466 the object into a nonstandard tagged JSON value (that JSON decoders
467 cannot decode).
468
469 It also causes "decode" to parse such tagged JSON values and
470 deserialise them via a call to the "THAW" method.
471
472 If $enable is false (the default), then "encode" will not consider
473 this type of conversion, and tagged JSON values will cause a parse
474 error in "decode", as if tags were not part of the grammar.
420 475
421 $json = $json->filter_json_object ([$coderef->($hashref)]) 476 $json = $json->filter_json_object ([$coderef->($hashref)])
422 When $coderef is specified, it will be called from "decode" each 477 When $coderef is specified, it will be called from "decode" each
423 time it decodes a JSON object. The only argument is a reference to 478 time it decodes a JSON object. The only argument is a reference to
424 the newly-created hash. If the code references returns a single 479 the newly-created hash. If the code references returns a single
… …
523 saving space. 578 saving space.
524 579
525 $json = $json->max_depth ([$maximum_nesting_depth]) 580 $json = $json->max_depth ([$maximum_nesting_depth])
526 $max_depth = $json->get_max_depth 581 $max_depth = $json->get_max_depth
527 Sets the maximum nesting level (default 512) accepted while encoding 582 Sets the maximum nesting level (default 512) accepted while encoding
528 or decoding. If the JSON text or Perl data structure has an equal or 583 or decoding. If a higher nesting level is detected in JSON text or a
529 higher nesting level then this limit, then the encoder and decoder 584 Perl data structure, then the encoder and decoder will stop and
530 will stop and croak at that point. 585 croak at that point.
531 586
532 Nesting level is defined by number of hash- or arrayrefs that the 587 Nesting level is defined by number of hash- or arrayrefs that the
533 encoder needs to traverse to reach a given point or the number of 588 encoder needs to traverse to reach a given point or the number of
534 "{" or "[" characters without their matching closing parenthesis 589 "{" or "[" characters without their matching closing parenthesis
535 crossed to reach a given character in a string. 590 crossed to reach a given character in a string.
536 591
537 Setting the maximum depth to one disallows any nesting, so that 592 Setting the maximum depth to one disallows any nesting, so that
538 ensures that the object is only a single hash/object or array. 593 ensures that the object is only a single hash/object or array.
539 594
540 The argument to "max_depth" will be rounded up to the next highest
541 power of two. If no argument is given, the highest possible setting 595 If no argument is given, the highest possible setting will be used,
542 will be used, which is rarely useful. 596 which is rarely useful.
597
598 Note that nesting is implemented by recursion in C. The default
599 value has been chosen to be as large as typical operating systems
600 allow without crashing.
543 601
544 See SECURITY CONSIDERATIONS, below, for more info on why this is 602 See SECURITY CONSIDERATIONS, below, for more info on why this is
545 useful. 603 useful.
546 604
547 $json = $json->max_size ([$maximum_string_size]) 605 $json = $json->max_size ([$maximum_string_size])
548 $max_size = $json->get_max_size 606 $max_size = $json->get_max_size
549 Set the maximum length a JSON text may have (in bytes) where 607 Set the maximum length a JSON text may have (in bytes) where
550 decoding is being attempted. The default is 0, meaning no limit. 608 decoding is being attempted. The default is 0, meaning no limit.
551 When "decode" is called on a string longer then this number of 609 When "decode" is called on a string that is longer then this many
552 characters it will not attempt to decode the string but throw an 610 bytes, it will not attempt to decode the string but throw an
553 exception. This setting has no effect on "encode" (yet). 611 exception. This setting has no effect on "encode" (yet).
554 612
555 The argument to "max_size" will be rounded up to the next highest
556 power of two (so may be more than requested). If no argument is
557 given, the limit check will be deactivated (same as when 0 is 613 If no argument is given, the limit check will be deactivated (same
558 specified). 614 as when 0 is specified).
559 615
560 See SECURITY CONSIDERATIONS, below, for more info on why this is 616 See SECURITY CONSIDERATIONS, below, for more info on why this is
561 useful. 617 useful.
562 618
563 $json_text = $json->encode ($perl_scalar) 619 $json_text = $json->encode ($perl_scalar)
564 Converts the given Perl data structure (a simple scalar or a 620 Converts the given Perl value or data structure to its JSON
565 reference to a hash or array) to its JSON representation. Simple 621 representation. Croaks on error.
566 scalars will be converted into JSON string or number sequences,
567 while references to arrays become JSON arrays and references to
568 hashes become JSON objects. Undefined Perl values (e.g. "undef")
569 become JSON "null" values. Neither "true" nor "false" values will be
570 generated.
571 622
572 $perl_scalar = $json->decode ($json_text) 623 $perl_scalar = $json->decode ($json_text)
573 The opposite of "encode": expects a JSON text and tries to parse it, 624 The opposite of "encode": expects a JSON text and tries to parse it,
574 returning the resulting simple scalar or reference. Croaks on error. 625 returning the resulting simple scalar or reference. Croaks on error.
575
576 JSON numbers and strings become simple Perl scalars. JSON arrays
577 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
578 becomes 1, "false" becomes 0 and "null" becomes "undef".
579 626
580 ($perl_scalar, $characters) = $json->decode_prefix ($json_text) 627 ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
581 This works like the "decode" method, but instead of raising an 628 This works like the "decode" method, but instead of raising an
582 exception when there is trailing garbage after the first JSON 629 exception when there is trailing garbage after the first JSON
583 object, it will silently stop parsing there and return the number of 630 object, it will silently stop parsing there and return the number of
584 characters consumed so far. 631 characters consumed so far.
585 632
586 This is useful if your JSON texts are not delimited by an outer 633 This is useful if your JSON texts are not delimited by an outer
587 protocol (which is not the brightest thing to do in the first place)
588 and you need to know where the JSON text ends. 634 protocol and you need to know where the JSON text ends.
589 635
590 JSON::XS->new->decode_prefix ("[1] the tail") 636 JSON::XS->new->decode_prefix ("[1] the tail")
591 => ([], 3) 637 => ([1], 3)
638
639INCREMENTAL PARSING
640 In some cases, there is the need for incremental parsing of JSON texts.
641 While this module always has to keep both JSON text and resulting Perl
642 data structure in memory at one time, it does allow you to parse a JSON
643 stream incrementally. It does so by accumulating text until it has a
644 full JSON object, which it then can decode. This process is similar to
645 using "decode_prefix" to see if a full JSON object is available, but is
646 much more efficient (and can be implemented with a minimum of method
647 calls).
648
649 JSON::XS will only attempt to parse the JSON text once it is sure it has
650 enough text to get a decisive result, using a very simple but truly
651 incremental parser. This means that it sometimes won't stop as early as
652 the full parser, for example, it doesn't detect mismatched parentheses.
653 The only thing it guarantees is that it starts decoding as soon as a
654 syntactically valid JSON text has been seen. This means you need to set
655 resource limits (e.g. "max_size") to ensure the parser will stop parsing
656 in the presence if syntax errors.
657
658 The following methods implement this incremental parser.
659
660 [void, scalar or list context] = $json->incr_parse ([$string])
661 This is the central parsing function. It can both append new text
662 and extract objects from the stream accumulated so far (both of
663 these functions are optional).
664
665 If $string is given, then this string is appended to the already
666 existing JSON fragment stored in the $json object.
667
668 After that, if the function is called in void context, it will
669 simply return without doing anything further. This can be used to
670 add more text in as many chunks as you want.
671
672 If the method is called in scalar context, then it will try to
673 extract exactly *one* JSON object. If that is successful, it will
674 return this object, otherwise it will return "undef". If there is a
675 parse error, this method will croak just as "decode" would do (one
676 can then use "incr_skip" to skip the erroneous part). This is the
677 most common way of using the method.
678
679 And finally, in list context, it will try to extract as many objects
680 from the stream as it can find and return them, or the empty list
681 otherwise. For this to work, there must be no separators (other than
682 whitespace) between the JSON objects or arrays, instead they must be
683 concatenated back-to-back. If an error occurs, an exception will be
684 raised as in the scalar context case. Note that in this case, any
685 previously-parsed JSON texts will be lost.
686
687 Example: Parse some JSON arrays/objects in a given string and return
688 them.
689
690 my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
691
692 $lvalue_string = $json->incr_text
693 This method returns the currently stored JSON fragment as an lvalue,
694 that is, you can manipulate it. This *only* works when a preceding
695 call to "incr_parse" in *scalar context* successfully returned an
696 object. Under all other circumstances you must not call this
697 function (I mean it. although in simple tests it might actually
698 work, it *will* fail under real world conditions). As a special
699 exception, you can also call this method before having parsed
700 anything.
701
702 That means you can only use this function to look at or manipulate
703 text before or after complete JSON objects, not while the parser is
704 in the middle of parsing a JSON object.
705
706 This function is useful in two cases: a) finding the trailing text
707 after a JSON object or b) parsing multiple JSON objects separated by
708 non-JSON text (such as commas).
709
710 $json->incr_skip
711 This will reset the state of the incremental parser and will remove
712 the parsed text from the input buffer so far. This is useful after
713 "incr_parse" died, in which case the input buffer and incremental
714 parser state is left unchanged, to skip the text parsed so far and
715 to reset the parse state.
716
717 The difference to "incr_reset" is that only text until the parse
718 error occurred is removed.
719
720 $json->incr_reset
721 This completely resets the incremental parser, that is, after this
722 call, it will be as if the parser had never parsed anything.
723
724 This is useful if you want to repeatedly parse JSON objects and want
725 to ignore any trailing data, which means you have to reset the
726 parser after each successful decode.
727
728 LIMITATIONS
729 All options that affect decoding are supported, except "allow_nonref".
730 The reason for this is that it cannot be made to work sensibly: JSON
731 objects and arrays are self-delimited, i.e. you can concatenate them
732 back to back and still decode them perfectly. This does not hold true
733 for JSON numbers, however.
734
735 For example, is the string 1 a single JSON number, or is it simply the
736 start of 12? Or is 12 a single JSON number, or the concatenation of 1
737 and 2? In neither case you can tell, and this is why JSON::XS takes the
738 conservative route and disallows this case.
739
740 EXAMPLES
741 Some examples will make all this clearer. First, a simple example that
742 works similarly to "decode_prefix": We want to decode the JSON object at
743 the start of a string and identify the portion after the JSON object:
744
745 my $text = "[1,2,3] hello";
746
747 my $json = new JSON::XS;
748
749 my $obj = $json->incr_parse ($text)
750 or die "expected JSON object or array at beginning of string";
751
752 my $tail = $json->incr_text;
753 # $tail now contains " hello"
754
755 Easy, isn't it?
756
757 Now for a more complicated example: Imagine a hypothetical protocol
758 where you read some requests from a TCP stream, and each request is a
759 JSON array, without any separation between them (in fact, it is often
760 useful to use newlines as "separators", as these get interpreted as
761 whitespace at the start of the JSON text, which makes it possible to
762 test said protocol with "telnet"...).
763
764 Here is how you'd do it (it is trivial to write this in an event-based
765 manner):
766
767 my $json = new JSON::XS;
768
769 # read some data from the socket
770 while (sysread $socket, my $buf, 4096) {
771
772 # split and decode as many requests as possible
773 for my $request ($json->incr_parse ($buf)) {
774 # act on the $request
775 }
776 }
777
778 Another complicated example: Assume you have a string with JSON objects
779 or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
780 [3]"). To parse them, we have to skip the commas between the JSON texts,
781 and here is where the lvalue-ness of "incr_text" comes in useful:
782
783 my $text = "[1],[2], [3]";
784 my $json = new JSON::XS;
785
786 # void context, so no parsing done
787 $json->incr_parse ($text);
788
789 # now extract as many objects as possible. note the
790 # use of scalar context so incr_text can be called.
791 while (my $obj = $json->incr_parse) {
792 # do something with $obj
793
794 # now skip the optional comma
795 $json->incr_text =~ s/^ \s* , //x;
796 }
797
798 Now lets go for a very complex example: Assume that you have a gigantic
799 JSON array-of-objects, many gigabytes in size, and you want to parse it,
800 but you cannot load it into memory fully (this has actually happened in
801 the real world :).
802
803 Well, you lost, you have to implement your own JSON parser. But JSON::XS
804 can still help you: You implement a (very simple) array parser and let
805 JSON decode the array elements, which are all full JSON objects on their
806 own (this wouldn't work if the array elements could be JSON numbers, for
807 example):
808
809 my $json = new JSON::XS;
810
811 # open the monster
812 open my $fh, "<bigfile.json"
813 or die "bigfile: $!";
814
815 # first parse the initial "["
816 for (;;) {
817 sysread $fh, my $buf, 65536
818 or die "read error: $!";
819 $json->incr_parse ($buf); # void context, so no parsing
820
821 # Exit the loop once we found and removed(!) the initial "[".
822 # In essence, we are (ab-)using the $json object as a simple scalar
823 # we append data to.
824 last if $json->incr_text =~ s/^ \s* \[ //x;
825 }
826
827 # now we have the skipped the initial "[", so continue
828 # parsing all the elements.
829 for (;;) {
830 # in this loop we read data until we got a single JSON object
831 for (;;) {
832 if (my $obj = $json->incr_parse) {
833 # do something with $obj
834 last;
835 }
836
837 # add more data
838 sysread $fh, my $buf, 65536
839 or die "read error: $!";
840 $json->incr_parse ($buf); # void context, so no parsing
841 }
842
843 # in this loop we read data until we either found and parsed the
844 # separating "," between elements, or the final "]"
845 for (;;) {
846 # first skip whitespace
847 $json->incr_text =~ s/^\s*//;
848
849 # if we find "]", we are done
850 if ($json->incr_text =~ s/^\]//) {
851 print "finished.\n";
852 exit;
853 }
854
855 # if we find ",", we can continue with the next element
856 if ($json->incr_text =~ s/^,//) {
857 last;
858 }
859
860 # if we find anything else, we have a parse error!
861 if (length $json->incr_text) {
862 die "parse error near ", $json->incr_text;
863 }
864
865 # else add more data
866 sysread $fh, my $buf, 65536
867 or die "read error: $!";
868 $json->incr_parse ($buf); # void context, so no parsing
869 }
870
871 This is a complex example, but most of the complexity comes from the
872 fact that we are trying to be correct (bear with me if I am wrong, I
873 never ran the above example :).
592 874
593MAPPING 875MAPPING
594 This section describes how JSON::XS maps Perl values to JSON values and 876 This section describes how JSON::XS maps Perl values to JSON values and
595 vice versa. These mappings are designed to "do the right thing" in most 877 vice versa. These mappings are designed to "do the right thing" in most
596 circumstances automatically, preserving round-tripping characteristics 878 circumstances automatically, preserving round-tripping characteristics
… …
618 A JSON number becomes either an integer, numeric (floating point) or 900 A JSON number becomes either an integer, numeric (floating point) or
619 string scalar in perl, depending on its range and any fractional 901 string scalar in perl, depending on its range and any fractional
620 parts. On the Perl level, there is no difference between those as 902 parts. On the Perl level, there is no difference between those as
621 Perl handles all the conversion details, but an integer may take 903 Perl handles all the conversion details, but an integer may take
622 slightly less memory and might represent more values exactly than 904 slightly less memory and might represent more values exactly than
623 (floating point) numbers. 905 floating point numbers.
624 906
625 If the number consists of digits only, JSON::XS will try to 907 If the number consists of digits only, JSON::XS will try to
626 represent it as an integer value. If that fails, it will try to 908 represent it as an integer value. If that fails, it will try to
627 represent it as a numeric (floating point) value if that is possible 909 represent it as a numeric (floating point) value if that is possible
628 without loss of precision. Otherwise it will preserve the number as 910 without loss of precision. Otherwise it will preserve the number as
629 a string value. 911 a string value (in which case you lose roundtripping ability, as the
912 JSON number will be re-encoded to a JSON string).
630 913
631 Numbers containing a fractional or exponential part will always be 914 Numbers containing a fractional or exponential part will always be
632 represented as numeric (floating point) values, possibly at a loss 915 represented as numeric (floating point) values, possibly at a loss
633 of precision. 916 of precision (in which case you might lose perfect roundtripping
917 ability, but the JSON number will still be re-encoded as a JSON
918 number).
634 919
635 This might create round-tripping problems as numbers might become 920 Note that precision is not accuracy - binary floating point values
636 strings, but as Perl is typeless there is no other way to do it. 921 cannot represent most decimal fractions exactly, and when converting
922 from and to floating point, JSON::XS only guarantees precision up to
923 but not including the least significant bit.
637 924
638 true, false 925 true, false
639 These JSON atoms become "JSON::XS::true" and "JSON::XS::false", 926 These JSON atoms become "Types::Serialiser::true" and
640 respectively. They are overloaded to act almost exactly like the 927 "Types::Serialiser::false", respectively. They are overloaded to act
641 numbers 1 and 0. You can check whether a scalar is a JSON boolean by 928 almost exactly like the numbers 1 and 0. You can check whether a
642 using the "JSON::XS::is_bool" function. 929 scalar is a JSON boolean by using the "Types::Serialiser::is_bool"
930 function (after "use Types::Serialier", of course).
643 931
644 null 932 null
645 A JSON null atom becomes "undef" in Perl. 933 A JSON null atom becomes "undef" in Perl.
934
935 shell-style comments ("# *text*")
936 As a nonstandard extension to the JSON syntax that is enabled by the
937 "relaxed" setting, shell-style comments are allowed. They can start
938 anywhere outside strings and go till the end of the line.
939
940 tagged values ("(*tag*)*value*").
941 Another nonstandard extension to the JSON syntax, enabled with the
942 "allow_tags" setting, are tagged values. In this implementation, the
943 *tag* must be a perl package/class name encoded as a JSON string,
944 and the *value* must be a JSON array encoding optional constructor
945 arguments.
946
947 See "OBJECT SERIALISATION", below, for details.
646 948
647 PERL -> JSON 949 PERL -> JSON
648 The mapping from Perl to JSON is slightly more difficult, as Perl is a 950 The mapping from Perl to JSON is slightly more difficult, as Perl is a
649 truly typeless language, so we can only guess which JSON type is meant 951 truly typeless language, so we can only guess which JSON type is meant
650 by a Perl value. 952 by a Perl value.
651 953
652 hash references 954 hash references
653 Perl hash references become JSON objects. As there is no inherent 955 Perl hash references become JSON objects. As there is no inherent
654 ordering in hash keys (or JSON objects), they will usually be 956 ordering in hash keys (or JSON objects), they will usually be
655 encoded in a pseudo-random order that can change between runs of the 957 encoded in a pseudo-random order. JSON::XS can optionally sort the
656 same program but stays generally the same within a single run of a 958 hash keys (determined by the *canonical* flag), so the same
657 program. JSON::XS can optionally sort the hash keys (determined by 959 datastructure will serialise to the same JSON text (given same
658 the *canonical* flag), so the same datastructure will serialise to 960 settings and version of JSON::XS), but this incurs a runtime
659 the same JSON text (given same settings and version of JSON::XS), 961 overhead and is only rarely useful, e.g. when you want to compare
660 but this incurs a runtime overhead and is only rarely useful, e.g. 962 some JSON text against another for equality.
661 when you want to compare some JSON text against another for
662 equality.
663 963
664 array references 964 array references
665 Perl array references become JSON arrays. 965 Perl array references become JSON arrays.
666 966
667 other references 967 other references
668 Other unblessed references are generally not allowed and will cause 968 Other unblessed references are generally not allowed and will cause
669 an exception to be thrown, except for references to the integers 0 969 an exception to be thrown, except for references to the integers 0
670 and 1, which get turned into "false" and "true" atoms in JSON. You 970 and 1, which get turned into "false" and "true" atoms in JSON.
671 can also use "JSON::XS::false" and "JSON::XS::true" to improve 971
972 Since "JSON::XS" uses the boolean model from Types::Serialiser, you
973 can also "use Types::Serialiser" and then use
974 "Types::Serialiser::false" and "Types::Serialiser::true" to improve
672 readability. 975 readability.
673 976
977 use Types::Serialiser;
674 to_json [\0,JSON::XS::true] # yields [false,true] 978 encode_json [\0, Types::Serialiser::true] # yields [false,true]
675 979
676 JSON::XS::true, JSON::XS::false 980 Types::Serialiser::true, Types::Serialiser::false
677 These special values become JSON true and JSON false values, 981 These special values from the Types::Serialiser module become JSON
678 respectively. You can also use "\1" and "\0" directly if you want. 982 true and JSON false values, respectively. You can also use "\1" and
983 "\0" directly if you want.
679 984
680 blessed objects 985 blessed objects
681 Blessed objects are not allowed. JSON::XS currently tries to encode 986 Blessed objects are not directly representable in JSON, but
682 their underlying representation (hash- or arrayref), but this 987 "JSON::XS" allows various ways of handling objects. See "OBJECT
683 behaviour might change in future versions. 988 SERIALISATION", below, for details.
684 989
685 simple scalars 990 simple scalars
686 Simple Perl scalars (any scalar that is not a reference) are the 991 Simple Perl scalars (any scalar that is not a reference) are the
687 most difficult objects to encode: JSON::XS will encode undefined 992 most difficult objects to encode: JSON::XS will encode undefined
688 scalars as JSON null value, scalars that have last been used in a 993 scalars as JSON "null" values, scalars that have last been used in a
689 string context before encoding as JSON strings and anything else as 994 string context before encoding as JSON strings, and anything else as
690 number value: 995 number value:
691 996
692 # dump as number 997 # dump as number
693 to_json [2] # yields [2] 998 encode_json [2] # yields [2]
694 to_json [-3.0e17] # yields [-3e+17] 999 encode_json [-3.0e17] # yields [-3e+17]
695 my $value = 5; to_json [$value] # yields [5] 1000 my $value = 5; encode_json [$value] # yields [5]
696 1001
697 # used as string, so dump as string 1002 # used as string, so dump as string
698 print $value; 1003 print $value;
699 to_json [$value] # yields ["5"] 1004 encode_json [$value] # yields ["5"]
700 1005
701 # undef becomes null 1006 # undef becomes null
702 to_json [undef] # yields [null] 1007 encode_json [undef] # yields [null]
703 1008
704 You can force the type to be a JSON string by stringifying it: 1009 You can force the type to be a JSON string by stringifying it:
705 1010
706 my $x = 3.1; # some variable containing a number 1011 my $x = 3.1; # some variable containing a number
707 "$x"; # stringified 1012 "$x"; # stringified
… …
713 my $x = "3"; # some variable containing a string 1018 my $x = "3"; # some variable containing a string
714 $x += 0; # numify it, ensuring it will be dumped as a number 1019 $x += 0; # numify it, ensuring it will be dumped as a number
715 $x *= 1; # same thing, the choice is yours. 1020 $x *= 1; # same thing, the choice is yours.
716 1021
717 You can not currently force the type in other, less obscure, ways. 1022 You can not currently force the type in other, less obscure, ways.
718 Tell me if you need this capability. 1023 Tell me if you need this capability (but don't forget to explain why
1024 it's needed :).
719 1025
720COMPARISON 1026 Note that numerical precision has the same meaning as under Perl (so
721 As already mentioned, this module was created because none of the 1027 binary to decimal conversion follows the same rules as in Perl,
722 existing JSON modules could be made to work correctly. First I will 1028 which can differ to other languages). Also, your perl interpreter
723 describe the problems (or pleasures) I encountered with various existing 1029 might expose extensions to the floating point numbers of your
724 JSON modules, followed by some benchmark values. JSON::XS was designed 1030 platform, such as infinities or NaN's - these cannot be represented
725 not to suffer from any of these problems or limitations. 1031 in JSON, and it is an error to pass those in.
726 1032
727 JSON 1.07 1033 OBJECT SERIALISATION
728 Slow (but very portable, as it is written in pure Perl). 1034 As JSON cannot directly represent Perl objects, you have to choose
1035 between a pure JSON representation (without the ability to deserialise
1036 the object automatically again), and a nonstandard extension to the JSON
1037 syntax, tagged values.
729 1038
730 Undocumented/buggy Unicode handling (how JSON handles Unicode values 1039 SERIALISATION
731 is undocumented. One can get far by feeding it Unicode strings and 1040 What happens when "JSON::XS" encounters a Perl object depends on the
732 doing en-/decoding oneself, but Unicode escapes are not working 1041 "allow_blessed", "convert_blessed" and "allow_tags" settings, which are
1042 used in this order:
1043
1044 1. "allow_tags" is enabled and the object has a "FREEZE" method.
1045 In this case, "JSON::XS" uses the Types::Serialiser object
1046 serialisation protocol to create a tagged JSON value, using a
1047 nonstandard extension to the JSON syntax.
1048
1049 This works by invoking the "FREEZE" method on the object, with the
1050 first argument being the object to serialise, and the second
1051 argument being the constant string "JSON" to distinguish it from
1052 other serialisers.
1053
1054 The "FREEZE" method can return any number of values (i.e. zero or
1055 more). These values and the paclkage/classname of the object will
1056 then be encoded as a tagged JSON value in the following format:
1057
1058 ("classname")[FREEZE return values...]
1059
1060 e.g.:
1061
1062 ("URI")["http://www.google.com/"]
1063 ("MyDate")[2013,10,29]
1064 ("ImageData::JPEG")["Z3...VlCg=="]
1065
1066 For example, the hypothetical "My::Object" "FREEZE" method might use
1067 the objects "type" and "id" members to encode the object:
1068
1069 sub My::Object::FREEZE {
1070 my ($self, $serialiser) = @_;
1071
1072 ($self->{type}, $self->{id})
1073 }
1074
1075 2. "convert_blessed" is enabled and the object has a "TO_JSON" method.
1076 In this case, the "TO_JSON" method of the object is invoked in
1077 scalar context. It must return a single scalar that can be directly
1078 encoded into JSON. This scalar replaces the object in the JSON text.
1079
1080 For example, the following "TO_JSON" method will convert all URI
1081 objects to JSON strings when serialised. The fatc that these values
1082 originally were URI objects is lost.
1083
1084 sub URI::TO_JSON {
1085 my ($uri) = @_;
1086 $uri->as_string
1087 }
1088
1089 3. "allow_blessed" is enabled.
1090 The object will be serialised as a JSON null value.
1091
1092 4. none of the above
1093 If none of the settings are enabled or the respective methods are
1094 missing, "JSON::XS" throws an exception.
1095
1096 DESERIALISATION
1097 For deserialisation there are only two cases to consider: either
1098 nonstandard tagging was used, in which case "allow_tags" decides, or
1099 objects cannot be automatically be deserialised, in which case you can
1100 use postprocessing or the "filter_json_object" or
1101 "filter_json_single_key_object" callbacks to get some real objects our
1102 of your JSON.
1103
1104 This section only considers the tagged value case: I a tagged JSON
1105 object is encountered during decoding and "allow_tags" is disabled, a
1106 parse error will result (as if tagged values were not part of the
1107 grammar).
1108
1109 If "allow_tags" is enabled, "JSON::XS" will look up the "THAW" method of
1110 the package/classname used during serialisation (it will not attempt to
1111 load the package as a Perl module). If there is no such method, the
1112 decoding will fail with an error.
1113
1114 Otherwise, the "THAW" method is invoked with the classname as first
1115 argument, the constant string "JSON" as second argument, and all the
1116 values from the JSON array (the values originally returned by the
1117 "FREEZE" method) as remaining arguments.
1118
1119 The method must then return the object. While technically you can return
1120 any Perl scalar, you might have to enable the "enable_nonref" setting to
1121 make that work in all cases, so better return an actual blessed
1122 reference.
1123
1124 As an example, let's implement a "THAW" function that regenerates the
1125 "My::Object" from the "FREEZE" example earlier:
1126
1127 sub My::Object::THAW {
1128 my ($class, $serialiser, $type, $id) = @_;
1129
1130 $class->new (type => $type, id => $id)
1131 }
1132
1133ENCODING/CODESET FLAG NOTES
1134 The interested reader might have seen a number of flags that signify
1135 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
1136 some confusion on what these do, so here is a short comparison:
1137
1138 "utf8" controls whether the JSON text created by "encode" (and expected
1139 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
1140 control whether "encode" escapes character values outside their
1141 respective codeset range. Neither of these flags conflict with each
1142 other, although some combinations make less sense than others.
1143
1144 Care has been taken to make all flags symmetrical with respect to
1145 "encode" and "decode", that is, texts encoded with any combination of
1146 these flag values will be correctly decoded when the same flags are used
1147 - in general, if you use different flag settings while encoding vs. when
1148 decoding you likely have a bug somewhere.
1149
1150 Below comes a verbose discussion of these flags. Note that a "codeset"
1151 is simply an abstract set of character-codepoint pairs, while an
1152 encoding takes those codepoint numbers and *encodes* them, in our case
1153 into octets. Unicode is (among other things) a codeset, UTF-8 is an
1154 encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
1155 encodings at the same time, which can be confusing.
1156
1157 "utf8" flag disabled
1158 When "utf8" is disabled (the default), then "encode"/"decode"
1159 generate and expect Unicode strings, that is, characters with high
1160 ordinal Unicode values (> 255) will be encoded as such characters,
1161 and likewise such characters are decoded as-is, no changes to them
1162 will be done, except "(re-)interpreting" them as Unicode codepoints
1163 or Unicode characters, respectively (to Perl, these are the same
1164 thing in strings unless you do funny/weird/dumb stuff).
1165
1166 This is useful when you want to do the encoding yourself (e.g. when
1167 you want to have UTF-16 encoded JSON texts) or when some other layer
1168 does the encoding for you (for example, when printing to a terminal
1169 using a filehandle that transparently encodes to UTF-8 you certainly
1170 do NOT want to UTF-8 encode your data first and have Perl encode it
1171 another time).
1172
1173 "utf8" flag enabled
1174 If the "utf8"-flag is enabled, "encode"/"decode" will encode all
1175 characters using the corresponding UTF-8 multi-byte sequence, and
1176 will expect your input strings to be encoded as UTF-8, that is, no
1177 "character" of the input string must have any value > 255, as UTF-8
1178 does not allow that.
1179
1180 The "utf8" flag therefore switches between two modes: disabled means
1181 you will get a Unicode string in Perl, enabled means you get an
1182 UTF-8 encoded octet/binary string in Perl.
1183
1184 "latin1" or "ascii" flags enabled
1185 With "latin1" (or "ascii") enabled, "encode" will escape characters
1186 with ordinal values > 255 (> 127 with "ascii") and encode the
1187 remaining characters as specified by the "utf8" flag.
1188
1189 If "utf8" is disabled, then the result is also correctly encoded in
1190 those character sets (as both are proper subsets of Unicode, meaning
1191 that a Unicode string with all character values < 256 is the same
1192 thing as a ISO-8859-1 string, and a Unicode string with all
1193 character values < 128 is the same thing as an ASCII string in
733 properly). 1194 Perl).
734 1195
735 No round-tripping (strings get clobbered if they look like numbers, 1196 If "utf8" is enabled, you still get a correct UTF-8-encoded string,
736 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that 1197 regardless of these flags, just some more characters will be escaped
737 will decode into the number 2. 1198 using "\uXXXX" then before.
738 1199
739 JSON::PC 0.01 1200 Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
740 Very fast. 1201 encoding, while ASCII-encoded strings are. That is because the
1202 ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
1203 *codeset* being a subset of Unicode), while ASCII is.
741 1204
742 Undocumented/buggy Unicode handling. 1205 Surprisingly, "decode" will ignore these flags and so treat all
1206 input values as governed by the "utf8" flag. If it is disabled, this
1207 allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
1208 strict subsets of Unicode. If it is enabled, you can correctly
1209 decode UTF-8 encoded strings.
743 1210
744 No round-tripping. 1211 So neither "latin1" nor "ascii" are incompatible with the "utf8"
1212 flag - they only govern when the JSON output engine escapes a
1213 character or not.
745 1214
746 Has problems handling many Perl values (e.g. regex results and other 1215 The main use for "latin1" is to relatively efficiently store binary
747 magic values will make it croak). 1216 data as JSON, at the expense of breaking compatibility with most
1217 JSON decoders.
748 1218
749 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 1219 The main use for "ascii" is to force the output to not contain
750 which is not a valid JSON text. 1220 characters with values > 127, which means you can interpret the
1221 resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
1222 any character set and 8-bit-encoding, and still get the same data
1223 structure back. This is useful when your channel for JSON transfer
1224 is not 8-bit clean or the encoding might be mangled in between (e.g.
1225 in mail), and works because ASCII is a proper subset of most 8-bit
1226 and multibyte encodings in use in the world.
751 1227
752 Unmaintained (maintainer unresponsive for many months, bugs are not 1228 JSON and ECMAscript
753 getting fixed). 1229 JSON syntax is based on how literals are represented in javascript (the
1230 not-standardised predecessor of ECMAscript) which is presumably why it
1231 is called "JavaScript Object Notation".
754 1232
755 JSON::Syck 0.21 1233 However, JSON is not a subset (and also not a superset of course) of
756 Very buggy (often crashes). 1234 ECMAscript (the standard) or javascript (whatever browsers actually
1235 implement).
757 1236
758 Very inflexible (no human-readable format supported, format pretty 1237 If you want to use javascript's "eval" function to "parse" JSON, you
759 much undocumented. I need at least a format for easy reading by 1238 might run into parse errors for valid JSON texts, or the resulting data
760 humans and a single-line compact format for use in a protocol, and 1239 structure might not be queryable:
761 preferably a way to generate ASCII-only JSON texts).
762 1240
763 Completely broken (and confusingly documented) Unicode handling 1241 One of the problems is that U+2028 and U+2029 are valid characters
764 (Unicode escapes are not working properly, you need to set 1242 inside JSON strings, but are not allowed in ECMAscript string literals,
765 ImplicitUnicode to *different* values on en- and decoding to get 1243 so the following Perl fragment will not output something that can be
766 symmetric behaviour). 1244 guaranteed to be parsable by javascript's "eval":
767 1245
768 No round-tripping (simple cases work, but this depends on whether 1246 use JSON::XS;
769 the scalar value was used in a numeric context or not).
770 1247
771 Dumping hashes may skip hash values depending on iterator state. 1248 print encode_json [chr 0x2028];
772 1249
773 Unmaintained (maintainer unresponsive for many months, bugs are not 1250 The right fix for this is to use a proper JSON parser in your javascript
774 getting fixed). 1251 programs, and not rely on "eval" (see for example Douglas Crockford's
1252 json2.js parser).
775 1253
776 Does not check input for validity (i.e. will accept non-JSON input 1254 If this is not an option, you can, as a stop-gap measure, simply encode
777 and return "something" instead of raising an exception. This is a 1255 to ASCII-only JSON:
778 security issue: imagine two banks transferring money between each
779 other using JSON. One bank might parse a given non-JSON request and
780 deduct money, while the other might reject the transaction with a
781 syntax error. While a good protocol will at least recover, that is
782 extra unnecessary work and the transaction will still not succeed).
783 1256
784 JSON::DWIW 0.04 1257 use JSON::XS;
785 Very fast. Very natural. Very nice.
786 1258
787 Undocumented Unicode handling (but the best of the pack. Unicode 1259 print JSON::XS->new->ascii->encode ([chr 0x2028]);
788 escapes still don't get parsed properly).
789 1260
790 Very inflexible. 1261 Note that this will enlarge the resulting JSON text quite a bit if you
1262 have many non-ASCII characters. You might be tempted to run some regexes
1263 to only escape U+2028 and U+2029, e.g.:
791 1264
792 No round-tripping. 1265 # DO NOT USE THIS!
1266 my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
1267 $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
1268 $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
1269 print $json;
793 1270
794 Does not generate valid JSON texts (key strings are often unquoted, 1271 Note that *this is a bad idea*: the above only works for U+2028 and
795 empty keys result in nothing being output) 1272 U+2029 and thus only for fully ECMAscript-compliant parsers. Many
1273 existing javascript implementations, however, have issues with other
1274 characters as well - using "eval" naively simply *will* cause problems.
796 1275
797 Does not check input for validity. 1276 Another problem is that some javascript implementations reserve some
1277 property names for their own purposes (which probably makes them
1278 non-ECMAscript-compliant). For example, Iceweasel reserves the
1279 "__proto__" property name for its own purposes.
1280
1281 If that is a problem, you could parse try to filter the resulting JSON
1282 output for these property strings, e.g.:
1283
1284 $json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
1285
1286 This works because "__proto__" is not valid outside of strings, so every
1287 occurrence of ""__proto__"\s*:" must be a string used as property name.
1288
1289 If you know of other incompatibilities, please let me know.
798 1290
799 JSON and YAML 1291 JSON and YAML
800 You often hear that JSON is a subset (or a close subset) of YAML. This 1292 You often hear that JSON is a subset of YAML. This is, however, a mass
801 is, however, a mass hysteria and very far from the truth. In general, 1293 hysteria(*) and very far from the truth (as of the time of this
802 there is no way to configure JSON::XS to output a data structure as 1294 writing), so let me state it clearly: *in general, there is no way to
803 valid YAML. 1295 configure JSON::XS to output a data structure as valid YAML* that works
1296 in all cases.
804 1297
805 If you really must use JSON::XS to generate YAML, you should use this 1298 If you really must use JSON::XS to generate YAML, you should use this
806 algorithm (subject to change in future versions): 1299 algorithm (subject to change in future versions):
807 1300
808 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1301 my $to_yaml = JSON::XS->new->utf8->space_after (1);
809 my $yaml = $to_yaml->encode ($ref) . "\n"; 1302 my $yaml = $to_yaml->encode ($ref) . "\n";
810 1303
811 This will usually generate JSON texts that also parse as valid YAML. 1304 This will *usually* generate JSON texts that also parse as valid YAML.
812 Please note that YAML has hardcoded limits on (simple) object key 1305 Please note that YAML has hardcoded limits on (simple) object key
813 lengths that JSON doesn't have, so you should make sure that your hash 1306 lengths that JSON doesn't have and also has different and incompatible
1307 unicode character escape syntax, so you should make sure that your hash
814 keys are noticeably shorter than the 1024 characters YAML allows. 1308 keys are noticeably shorter than the 1024 "stream characters" YAML
1309 allows and that you do not have characters with codepoint values outside
1310 the Unicode BMP (basic multilingual page). YAML also does not allow "\/"
1311 sequences in strings (which JSON::XS does not *currently* generate, but
1312 other JSON generators might).
815 1313
816 There might be other incompatibilities that I am not aware of. In 1314 There might be other incompatibilities that I am not aware of (or the
1315 YAML specification has been changed yet again - it does so quite often).
817 general you should not try to generate YAML with a JSON generator or 1316 In general you should not try to generate YAML with a JSON generator or
818 vice versa, or try to parse JSON with a YAML parser or vice versa: 1317 vice versa, or try to parse JSON with a YAML parser or vice versa:
819 chances are high that you will run into severe interoperability 1318 chances are high that you will run into severe interoperability problems
820 problems. 1319 when you least expect it.
1320
1321 (*) I have been pressured multiple times by Brian Ingerson (one of the
1322 authors of the YAML specification) to remove this paragraph, despite
1323 him acknowledging that the actual incompatibilities exist. As I was
1324 personally bitten by this "JSON is YAML" lie, I refused and said I
1325 will continue to educate people about these issues, so others do not
1326 run into the same problem again and again. After this, Brian called
1327 me a (quote)*complete and worthless idiot*(unquote).
1328
1329 In my opinion, instead of pressuring and insulting people who
1330 actually clarify issues with YAML and the wrong statements of some
1331 of its proponents, I would kindly suggest reading the JSON spec
1332 (which is not that difficult or long) and finally make YAML
1333 compatible to it, and educating users about the changes, instead of
1334 spreading lies about the real compatibility for many *years* and
1335 trying to silence people who point out that it isn't true.
1336
1337 Addendum/2009: the YAML 1.2 spec is still incompatible with JSON,
1338 even though the incompatibilities have been documented (and are
1339 known to Brian) for many years and the spec makes explicit claims
1340 that YAML is a superset of JSON. It would be so easy to fix, but
1341 apparently, bullying people and corrupting userdata is so much
1342 easier.
821 1343
822 SPEED 1344 SPEED
823 It seems that JSON::XS is surprisingly fast, as shown in the following 1345 It seems that JSON::XS is surprisingly fast, as shown in the following
824 tables. They have been generated with the help of the "eg/bench" program 1346 tables. They have been generated with the help of the "eg/bench" program
825 in the JSON::XS distribution, to make it easy to compare on your own 1347 in the JSON::XS distribution, to make it easy to compare on your own
826 system. 1348 system.
827 1349
828 First comes a comparison between various modules using a very short 1350 First comes a comparison between various modules using a very short
829 single-line JSON string: 1351 single-line JSON string (also available at
1352 <http://dist.schmorp.de/misc/json/short.json>).
830 1353
831 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1354 {"method": "handleMessage", "params": ["user1",
832 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1355 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1356 1, 0]}
833 1357
834 It shows the number of encodes/decodes per second (JSON::XS uses the 1358 It shows the number of encodes/decodes per second (JSON::XS uses the
835 functional interface, while JSON::XS/2 uses the OO interface with 1359 functional interface, while JSON::XS/2 uses the OO interface with
836 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). 1360 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink.
837 Higher is better: 1361 JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses
1362 the from_json method). Higher is better:
838 1363
839 module | encode | decode | 1364 module | encode | decode |
840 -----------|------------|------------| 1365 --------------|------------|------------|
841 JSON 1.x | 4990.842 | 4088.813 | 1366 JSON::DWIW/DS | 86302.551 | 102300.098 |
842 JSON::DWIW | 51653.990 | 71575.154 | 1367 JSON::DWIW/FJ | 86302.551 | 75983.768 |
843 JSON::PC | 65948.176 | 74631.744 | 1368 JSON::PP | 15827.562 | 6638.658 |
844 JSON::PP | 8931.652 | 3817.168 | 1369 JSON::Syck | 63358.066 | 47662.545 |
845 JSON::Syck | 24877.248 | 27776.848 | 1370 JSON::XS | 511500.488 | 511500.488 |
846 JSON::XS | 388361.481 | 227951.304 | 1371 JSON::XS/2 | 291271.111 | 388361.481 |
847 JSON::XS/2 | 227951.304 | 218453.333 | 1372 JSON::XS/3 | 361577.931 | 361577.931 |
848 JSON::XS/3 | 338250.323 | 218453.333 | 1373 Storable | 66788.280 | 265462.278 |
849 Storable | 16500.016 | 135300.129 |
850 -----------+------------+------------+ 1374 --------------+------------+------------+
851 1375
852 That is, JSON::XS is about five times faster than JSON::DWIW on 1376 That is, JSON::XS is almost six times faster than JSON::DWIW on
853 encoding, about three times faster on decoding, and over forty times 1377 encoding, about five times faster on decoding, and over thirty to
854 faster than JSON, even with pretty-printing and key sorting. It also 1378 seventy times faster than JSON's pure perl implementation. It also
855 compares favourably to Storable for small amounts of data. 1379 compares favourably to Storable for small amounts of data.
856 1380
857 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1381 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
858 search API (http://nanoref.com/yahooapis/mgPdGg): 1382 search API (<http://dist.schmorp.de/misc/json/long.json>).
859 1383
860 module | encode | decode | 1384 module | encode | decode |
861 -----------|------------|------------| 1385 --------------|------------|------------|
862 JSON 1.x | 55.260 | 34.971 | 1386 JSON::DWIW/DS | 1647.927 | 2673.916 |
863 JSON::DWIW | 825.228 | 1082.513 | 1387 JSON::DWIW/FJ | 1630.249 | 2596.128 |
864 JSON::PC | 3571.444 | 2394.829 |
865 JSON::PP | 210.987 | 32.574 | 1388 JSON::PP | 400.640 | 62.311 |
866 JSON::Syck | 552.551 | 787.544 | 1389 JSON::Syck | 1481.040 | 1524.869 |
867 JSON::XS | 5780.463 | 4854.519 | 1390 JSON::XS | 20661.596 | 9541.183 |
868 JSON::XS/2 | 3869.998 | 4798.975 | 1391 JSON::XS/2 | 10683.403 | 9416.938 |
869 JSON::XS/3 | 5862.880 | 4798.975 | 1392 JSON::XS/3 | 20661.596 | 9400.054 |
870 Storable | 4445.002 | 5235.027 | 1393 Storable | 19765.806 | 10000.725 |
871 -----------+------------+------------+ 1394 --------------+------------+------------+
872 1395
873 Again, JSON::XS leads by far (except for Storable which non-surprisingly 1396 Again, JSON::XS leads by far (except for Storable which non-surprisingly
874 decodes faster). 1397 decodes a bit faster).
875 1398
876 On large strings containing lots of high Unicode characters, some 1399 On large strings containing lots of high Unicode characters, some
877 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the 1400 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
878 result will be broken due to missing (or wrong) Unicode handling. Others 1401 result will be broken due to missing (or wrong) Unicode handling. Others
879 refuse to decode or encode properly, so it was impossible to prepare a 1402 refuse to decode or encode properly, so it was impossible to prepare a
… …
900 Third, JSON::XS recurses using the C stack when decoding objects and 1423 Third, JSON::XS recurses using the C stack when decoding objects and
901 arrays. The C stack is a limited resource: for instance, on my amd64 1424 arrays. The C stack is a limited resource: for instance, on my amd64
902 machine with 8MB of stack size I can decode around 180k nested arrays 1425 machine with 8MB of stack size I can decode around 180k nested arrays
903 but only 14k nested JSON objects (due to perl itself recursing deeply on 1426 but only 14k nested JSON objects (due to perl itself recursing deeply on
904 croak to free the temporary). If that is exceeded, the program crashes. 1427 croak to free the temporary). If that is exceeded, the program crashes.
905 to be conservative, the default nesting limit is set to 512. If your 1428 To be conservative, the default nesting limit is set to 512. If your
906 process has a smaller stack, you should adjust this setting accordingly 1429 process has a smaller stack, you should adjust this setting accordingly
907 with the "max_depth" method. 1430 with the "max_depth" method.
908 1431
909 And last but least, something else could bomb you that I forgot to think 1432 Something else could bomb you, too, that I forgot to think of. In that
910 of. In that case, you get to keep the pieces. I am always open for 1433 case, you get to keep the pieces. I am always open for hints, though...
911 hints, though... 1434
1435 Also keep in mind that JSON::XS might leak contents of your Perl data
1436 structures in its error messages, so when you serialise sensitive
1437 information you might want to make sure that exceptions thrown by
1438 JSON::XS will not end up in front of untrusted eyes.
912 1439
913 If you are using JSON::XS to return packets to consumption by JavaScript 1440 If you are using JSON::XS to return packets to consumption by JavaScript
914 scripts in a browser you should have a look at 1441 scripts in a browser you should have a look at
915 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether 1442 <http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/>
916 you are vulnerable to some common attack vectors (which really are 1443 to see whether you are vulnerable to some common attack vectors (which
917 browser design bugs, but it is still you who will have to deal with it, 1444 really are browser design bugs, but it is still you who will have to
918 as major browser developers care only for features, not about doing 1445 deal with it, as major browser developers care only for features, not
919 security right). 1446 about getting security right).
920 1447
1448"OLD" VS. "NEW" JSON (RFC 4627 VS. RFC 7159)
1449 TL;DR: Due to security concerns, JSON::XS will not allow scalar data in
1450 JSON texts by default - you need to create your own JSON::XS object and
1451 enable "allow_nonref":
1452
1453 my $json = JSON::XS->new->allow_nonref;
1454
1455 $text = $json->encode ($data);
1456 $data = $json->decode ($text);
1457
1458 The long version: JSON being an important and supposedly stable format,
1459 the IETF standardised it as RFC 4627 in 2006. Unfortunately, the
1460 inventor of JSON, Dougles Crockford, unilaterally changed the definition
1461 of JSON in javascript. Rather than create a fork, the IETF decided to
1462 standardise the new syntax (apparently, so Iw as told, without finding
1463 it very amusing).
1464
1465 The biggest difference between thed original JSON and the new JSON is
1466 that the new JSON supports scalars (anything other than arrays and
1467 objects) at the toplevel of a JSON text. While this is strictly
1468 backwards compatible to older versions, it breaks a number of protocols
1469 that relied on sending JSON back-to-back, and is a minor security
1470 concern.
1471
1472 For example, imagine you have two banks communicating, and on one side,
1473 trhe JSON coder gets upgraded. Two messages, such as 10 and 1000 might
1474 then be confused to mean 101000, something that couldn't happen in the
1475 original JSON, because niether of these messages would be valid JSON.
1476
1477 If one side accepts these messages, then an upgrade in the coder on
1478 either side could result in this becoming exploitable.
1479
1480 This module has always allowed these messages as an optional extension,
1481 by default disabled. The security concerns are the reason why the
1482 default is still disabled, but future versions might/will likely upgrade
1483 to the newer RFC as default format, so you are advised to check your
1484 implementation and/or override the default with "->allow_nonref (0)" to
1485 ensure that future versions are safe.
1486
1487INTEROPERABILITY WITH OTHER MODULES
1488 "JSON::XS" uses the Types::Serialiser module to provide boolean
1489 constants. That means that the JSON true and false values will be
1490 comaptible to true and false values of other modules that do the same,
1491 such as JSON::PP and CBOR::XS.
1492
1493INTEROPERABILITY WITH OTHER JSON DECODERS
1494 As long as you only serialise data that can be directly expressed in
1495 JSON, "JSON::XS" is incapable of generating invalid JSON output (modulo
1496 bugs, but "JSON::XS" has found more bugs in the official JSON testsuite
1497 (1) than the official JSON testsuite has found in "JSON::XS" (0)).
1498
1499 When you have trouble decoding JSON generated by this module using other
1500 decoders, then it is very likely that you have an encoding mismatch or
1501 the other decoder is broken.
1502
1503 When decoding, "JSON::XS" is strict by default and will likely catch all
1504 errors. There are currently two settings that change this: "relaxed"
1505 makes "JSON::XS" accept (but not generate) some non-standard extensions,
1506 and "allow_tags" will allow you to encode and decode Perl objects, at
1507 the cost of not outputting valid JSON anymore.
1508
1509 TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
1510 When you use "allow_tags" to use the extended (and also nonstandard and
1511 invalid) JSON syntax for serialised objects, and you still want to
1512 decode the generated When you want to serialise objects, you can run a
1513 regex to replace the tagged syntax by standard JSON arrays (it only
1514 works for "normal" package names without comma, newlines or single
1515 colons). First, the readable Perl version:
1516
1517 # if your FREEZE methods return no values, you need this replace first:
1518 $json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[\s*\]/[$1]/gx;
1519
1520 # this works for non-empty constructor arg lists:
1521 $json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[/[$1,/gx;
1522
1523 And here is a less readable version that is easy to adapt to other
1524 languages:
1525
1526 $json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/[$1,/g;
1527
1528 Here is an ECMAScript version (same regex):
1529
1530 json = json.replace (/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/g, "[$1,");
1531
1532 Since this syntax converts to standard JSON arrays, it might be hard to
1533 distinguish serialised objects from normal arrays. You can prepend a
1534 "magic number" as first array element to reduce chances of a collision:
1535
1536 $json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;
1537
1538 And after decoding the JSON text, you could walk the data structure
1539 looking for arrays with a first element of
1540 "XU1peReLzT4ggEllLanBYq4G9VzliwKF".
1541
1542 The same approach can be used to create the tagged format with another
1543 encoder. First, you create an array with the magic string as first
1544 member, the classname as second, and constructor arguments last, encode
1545 it as part of your JSON structure, and then:
1546
1547 $json =~ s/\[\s*"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s*,\s*("([^\\":,]+|\\.|::)*")\s*,/($1)[/g;
1548
1549 Again, this has some limitations - the magic string must not be encoded
1550 with character escapes, and the constructor arguments must be non-empty.
1551
1552RFC7159
1553 Since this module was written, Google has written a new JSON RFC, RFC
1554 7159 (and RFC7158). Unfortunately, this RFC breaks compatibility with
1555 both the original JSON specification on www.json.org and RFC4627.
1556
1557 As far as I can see, you can get partial compatibility when parsing by
1558 using "->allow_nonref". However, consider the security implications of
1559 doing so.
1560
1561 I haven't decided yet when to break compatibility with RFC4627 by
1562 default (and potentially leave applications insecure) and change the
1563 default to follow RFC7159, but application authors are well advised to
1564 call "->allow_nonref(0)" even if this is the current default, if they
1565 cannot handle non-reference values, in preparation for the day when the
1566 default will change.
1567
921THREADS 1568(I-)THREADS
922 This module is *not* guaranteed to be thread safe and there are no plans 1569 This module is *not* guaranteed to be ithread (or MULTIPLICITY-) safe
923 to change this until Perl gets thread support (as opposed to the 1570 and there are no plans to change this. Note that perl's builtin
924 horribly slow so-called "threads" which are simply slow and bloated 1571 so-called theeads/ithreads are officially deprecated and should not be
925 process simulations - use fork, its *much* faster, cheaper, better). 1572 used.
926 1573
927 (It might actually work, but you have been warned). 1574THE PERILS OF SETLOCALE
1575 Sometimes people avoid the Perl locale support and directly call the
1576 system's setlocale function with "LC_ALL".
1577
1578 This breaks both perl and modules such as JSON::XS, as stringification
1579 of numbers no longer works correctly (e.g. "$x = 0.1; print "$x"+1"
1580 might print 1, and JSON::XS might output illegal JSON as JSON::XS relies
1581 on perl to stringify numbers).
1582
1583 The solution is simple: don't call "setlocale", or use it for only those
1584 categories you need, such as "LC_MESSAGES" or "LC_CTYPE".
1585
1586 If you need "LC_NUMERIC", you should enable it only around the code that
1587 actually needs it (avoiding stringification of numbers), and restore it
1588 afterwards.
928 1589
929BUGS 1590BUGS
930 While the goal of this module is to be correct, that unfortunately does 1591 While the goal of this module is to be correct, that unfortunately does
931 not mean its bug-free, only that I think its design is bug-free. It is 1592 not mean it's bug-free, only that I think its design is bug-free. If you
932 still relatively early in its development. If you keep reporting bugs
933 they will be fixed swiftly, though. 1593 keep reporting bugs they will be fixed swiftly, though.
934 1594
935 Please refrain from using rt.cpan.org or any other bug reporting 1595 Please refrain from using rt.cpan.org or any other bug reporting
936 service. I put the contact address into my modules for a reason. 1596 service. I put the contact address into my modules for a reason.
1597
1598SEE ALSO
1599 The json_xs command line utility for quick experiments.
937 1600
938AUTHOR 1601AUTHOR
939 Marc Lehmann <schmorp@schmorp.de> 1602 Marc Lehmann <schmorp@schmorp.de>
940 http://home.schmorp.de/ 1603 http://home.schmorp.de/
941 1604

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