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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
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)
7
4SYNOPSIS 8SYNOPSIS
5 use JSON::XS; 9 use JSON::XS;
6 10
7 # exported functions, they croak on error 11 # exported functions, they croak on error
8 # and expect/generate UTF-8 12 # and expect/generate UTF-8
9 13
10 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 14 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
11 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 15 $perl_hash_or_arrayref = from_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 16
17 # OO-interface 17 # OO-interface
18 18
19 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 19 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
20 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 20 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
… …
71FUNCTIONAL INTERFACE 71FUNCTIONAL INTERFACE
72 The following convinience methods are provided by this module. They are 72 The following convinience methods are provided by this module. They are
73 exported by default: 73 exported by default:
74 74
75 $json_text = to_json $perl_scalar 75 $json_text = to_json $perl_scalar
76 Converts the given Perl data structure (a simple scalar or a 76 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. 77 string (that is, the string contains octets only). Croaks on error.
79 78
80 This function call is functionally identical to: 79 This function call is functionally identical to:
81 80
82 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 81 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
83 82
84 except being faster. 83 except being faster.
85 84
86 $perl_scalar = from_json $json_text 85 $perl_scalar = from_json $json_text
87 The opposite of "to_json": expects an UTF-8 (binary) string and 86 The opposite of "to_json": expects an UTF-8 (binary) string and
88 tries to parse that as an UTF-8 encoded JSON text, returning the 87 tries to parse that as an UTF-8 encoded JSON text, returning the
89 resulting simple scalar or reference. Croaks on error. 88 resulting reference. Croaks on error.
90 89
91 This function call is functionally identical to: 90 This function call is functionally identical to:
92 91
93 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 92 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
94 93
… …
100 respectively and are used to represent JSON "true" and "false" 99 respectively and are used to represent JSON "true" and "false"
101 values in Perl. 100 values in Perl.
102 101
103 See MAPPING, below, for more information on how JSON values are 102 See MAPPING, below, for more information on how JSON values are
104 mapped to Perl. 103 mapped to Perl.
104
105A FEW NOTES ON UNICODE AND PERL
106 Since this often leads to confusion, here are a few very clear words on
107 how Unicode works in Perl, modulo bugs.
108
109 1. Perl strings can store characters with ordinal values > 255.
110 This enables you to store unicode characters as single characters in
111 a Perl string - very natural.
112
113 2. Perl does *not* associate an encoding with your strings.
114 Unless you force it to, e.g. when matching it against a regex, or
115 printing the scalar to a file, in which case Perl either interprets
116 your string as locale-encoded text, octets/binary, or as Unicode,
117 depending on various settings. In no case is an encoding stored
118 together with your data, it is *use* that decides encoding, not any
119 magical metadata.
120
121 3. The internal utf-8 flag has no meaning with regards to the encoding
122 of your string.
123 Just ignore that flag unless you debug a Perl bug, a module written
124 in XS or want to dive into the internals of perl. Otherwise it will
125 only confuse you, as, despite the name, it says nothing about how
126 your string is encoded. You can have unicode strings with that flag
127 set, with that flag clear, and you can have binary data with that
128 flag set and that flag clear. Other possibilities exist, too.
129
130 If you didn't know about that flag, just the better, pretend it
131 doesn't exist.
132
133 4. A "Unicode String" is simply a string where each character can be
134 validly interpreted as a Unicode codepoint.
135 If you have UTF-8 encoded data, it is no longer a Unicode string,
136 but a Unicode string encoded in UTF-8, giving you a binary string.
137
138 5. A string containing "high" (> 255) character values is *not* a UTF-8
139 string.
140 Its a fact. Learn to live with it.
141
142 I hope this helps :)
105 143
106OBJECT-ORIENTED INTERFACE 144OBJECT-ORIENTED INTERFACE
107 The object oriented interface lets you configure your own encoding or 145 The object oriented interface lets you configure your own encoding or
108 decoding style, within the limits of supported formats. 146 decoding style, within the limits of supported formats.
109 147
… …
244 282
245 Example, space_before and indent disabled, space_after enabled: 283 Example, space_before and indent disabled, space_after enabled:
246 284
247 {"key": "value"} 285 {"key": "value"}
248 286
287 $json = $json->relaxed ([$enable])
288 If $enable is true (or missing), then "decode" will accept some
289 extensions to normal JSON syntax (see below). "encode" will not be
290 affected in anyway. *Be aware that this option makes you accept
291 invalid JSON texts as if they were valid!*. I suggest only to use
292 this option to parse application-specific files written by humans
293 (configuration files, resource files etc.)
294
295 If $enable is false (the default), then "decode" will only accept
296 valid JSON texts.
297
298 Currently accepted extensions are:
299
300 * list items can have an end-comma
301 JSON *separates* array elements and key-value pairs with commas.
302 This can be annoying if you write JSON texts manually and want
303 to be able to quickly append elements, so this extension accepts
304 comma at the end of such items not just between them:
305
306 [
307 1,
308 2, <- this comma not normally allowed
309 ]
310 {
311 "k1": "v1",
312 "k2": "v2", <- this comma not normally allowed
313 }
314
315 * shell-style '#'-comments
316 Whenever JSON allows whitespace, shell-style comments are
317 additionally allowed. They are terminated by the first
318 carriage-return or line-feed character, after which more
319 white-space and comments are allowed.
320
321 [
322 1, # this comment not allowed in JSON
323 # neither this one...
324 ]
325
249 $json = $json->canonical ([$enable]) 326 $json = $json->canonical ([$enable])
250 If $enable is true (or missing), then the "encode" method will 327 If $enable is true (or missing), then the "encode" method will
251 output JSON objects by sorting their keys. This is adding a 328 output JSON objects by sorting their keys. This is adding a
252 comparatively high overhead. 329 comparatively high overhead.
253 330
… …
277 Example, encode a Perl scalar as JSON value with enabled 354 Example, encode a Perl scalar as JSON value with enabled
278 "allow_nonref", resulting in an invalid JSON text: 355 "allow_nonref", resulting in an invalid JSON text:
279 356
280 JSON::XS->new->allow_nonref->encode ("Hello, World!") 357 JSON::XS->new->allow_nonref->encode ("Hello, World!")
281 => "Hello, World!" 358 => "Hello, World!"
359
360 $json = $json->allow_blessed ([$enable])
361 If $enable is true (or missing), then the "encode" method will not
362 barf when it encounters a blessed reference. Instead, the value of
363 the convert_blessed option will decide wether "null"
364 ("convert_blessed" disabled or no "to_json" method found) or a
365 representation of the object ("convert_blessed" enabled and
366 "to_json" method found) is being encoded. Has no effect on "decode".
367
368 If $enable is false (the default), then "encode" will throw an
369 exception when it encounters a blessed object.
370
371 $json = $json->convert_blessed ([$enable])
372 If $enable is true (or missing), then "encode", upon encountering a
373 blessed object, will check for the availability of the "TO_JSON"
374 method on the object's class. If found, it will be called in scalar
375 context and the resulting scalar will be encoded instead of the
376 object. If no "TO_JSON" method is found, the value of
377 "allow_blessed" will decide what to do.
378
379 The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
380 returns other blessed objects, those will be handled in the same
381 way. "TO_JSON" must take care of not causing an endless recursion
382 cycle (== crash) in this case. The name of "TO_JSON" was chosen
383 because other methods called by the Perl core (== not by the user of
384 the object) are usually in upper case letters and to avoid
385 collisions with the "to_json" function.
386
387 This setting does not yet influence "decode" in any way, but in the
388 future, global hooks might get installed that influence "decode" and
389 are enabled by this setting.
390
391 If $enable is false, then the "allow_blessed" setting will decide
392 what to do when a blessed object is found.
393
394 $json = $json->filter_json_object ([$coderef->($hashref)])
395 When $coderef is specified, it will be called from "decode" each
396 time it decodes a JSON object. The only argument is a reference to
397 the newly-created hash. If the code references returns a single
398 scalar (which need not be a reference), this value (i.e. a copy of
399 that scalar to avoid aliasing) is inserted into the deserialised
400 data structure. If it returns an empty list (NOTE: *not* "undef",
401 which is a valid scalar), the original deserialised hash will be
402 inserted. This setting can slow down decoding considerably.
403
404 When $coderef is omitted or undefined, any existing callback will be
405 removed and "decode" will not change the deserialised hash in any
406 way.
407
408 Example, convert all JSON objects into the integer 5:
409
410 my $js = JSON::XS->new->filter_json_object (sub { 5 });
411 # returns [5]
412 $js->decode ('[{}]')
413 # throw an exception because allow_nonref is not enabled
414 # so a lone 5 is not allowed.
415 $js->decode ('{"a":1, "b":2}');
416
417 $json = $json->filter_json_single_key_object ($key [=>
418 $coderef->($value)])
419 Works remotely similar to "filter_json_object", but is only called
420 for JSON objects having a single key named $key.
421
422 This $coderef is called before the one specified via
423 "filter_json_object", if any. It gets passed the single value in the
424 JSON object. If it returns a single value, it will be inserted into
425 the data structure. If it returns nothing (not even "undef" but the
426 empty list), the callback from "filter_json_object" will be called
427 next, as if no single-key callback were specified.
428
429 If $coderef is omitted or undefined, the corresponding callback will
430 be disabled. There can only ever be one callback for a given key.
431
432 As this callback gets called less often then the
433 "filter_json_object" one, decoding speed will not usually suffer as
434 much. Therefore, single-key objects make excellent targets to
435 serialise Perl objects into, especially as single-key JSON objects
436 are as close to the type-tagged value concept as JSON gets (its
437 basically an ID/VALUE tuple). Of course, JSON does not support this
438 in any way, so you need to make sure your data never looks like a
439 serialised Perl hash.
440
441 Typical names for the single object key are "__class_whatever__", or
442 "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
443 things like "__class_md5sum(classname)__", to reduce the risk of
444 clashing with real hashes.
445
446 Example, decode JSON objects of the form "{ "__widget__" => <id> }"
447 into the corresponding $WIDGET{<id>} object:
448
449 # return whatever is in $WIDGET{5}:
450 JSON::XS
451 ->new
452 ->filter_json_single_key_object (__widget__ => sub {
453 $WIDGET{ $_[0] }
454 })
455 ->decode ('{"__widget__": 5')
456
457 # this can be used with a TO_JSON method in some "widget" class
458 # for serialisation to json:
459 sub WidgetBase::TO_JSON {
460 my ($self) = @_;
461
462 unless ($self->{id}) {
463 $self->{id} = ..get..some..id..;
464 $WIDGET{$self->{id}} = $self;
465 }
466
467 { __widget__ => $self->{id} }
468 }
282 469
283 $json = $json->shrink ([$enable]) 470 $json = $json->shrink ([$enable])
284 Perl usually over-allocates memory a bit when allocating space for 471 Perl usually over-allocates memory a bit when allocating space for
285 strings. This flag optionally resizes strings generated by either 472 strings. This flag optionally resizes strings generated by either
286 "encode" or "decode" to their minimum size possible. This can save 473 "encode" or "decode" to their minimum size possible. This can save
… …
319 crossed to reach a given character in a string. 506 crossed to reach a given character in a string.
320 507
321 Setting the maximum depth to one disallows any nesting, so that 508 Setting the maximum depth to one disallows any nesting, so that
322 ensures that the object is only a single hash/object or array. 509 ensures that the object is only a single hash/object or array.
323 510
324 The argument to "max_depth" will be rounded up to the next nearest 511 The argument to "max_depth" will be rounded up to the next highest
325 power of two. 512 power of two. If no argument is given, the highest possible setting
513 will be used, which is rarely useful.
514
515 See SECURITY CONSIDERATIONS, below, for more info on why this is
516 useful.
517
518 $json = $json->max_size ([$maximum_string_size])
519 Set the maximum length a JSON text may have (in bytes) where
520 decoding is being attempted. The default is 0, meaning no limit.
521 When "decode" is called on a string longer then this number of
522 characters it will not attempt to decode the string but throw an
523 exception. This setting has no effect on "encode" (yet).
524
525 The argument to "max_size" will be rounded up to the next highest
526 power of two (so may be more than requested). If no argument is
527 given, the limit check will be deactivated (same as when 0 is
528 specified).
326 529
327 See SECURITY CONSIDERATIONS, below, for more info on why this is 530 See SECURITY CONSIDERATIONS, below, for more info on why this is
328 useful. 531 useful.
329 532
330 $json_text = $json->encode ($perl_scalar) 533 $json_text = $json->encode ($perl_scalar)
… …
380 A JSON string becomes a string scalar in Perl - Unicode codepoints 583 A JSON string becomes a string scalar in Perl - Unicode codepoints
381 in JSON are represented by the same codepoints in the Perl string, 584 in JSON are represented by the same codepoints in the Perl string,
382 so no manual decoding is necessary. 585 so no manual decoding is necessary.
383 586
384 number 587 number
385 A JSON number becomes either an integer or numeric (floating point) 588 A JSON number becomes either an integer, numeric (floating point) or
386 scalar in perl, depending on its range and any fractional parts. On 589 string scalar in perl, depending on its range and any fractional
387 the Perl level, there is no difference between those as Perl handles 590 parts. On the Perl level, there is no difference between those as
388 all the conversion details, but an integer may take slightly less 591 Perl handles all the conversion details, but an integer may take
389 memory and might represent more values exactly than (floating point) 592 slightly less memory and might represent more values exactly than
390 numbers. 593 (floating point) numbers.
594
595 If the number consists of digits only, JSON::XS will try to
596 represent it as an integer value. If that fails, it will try to
597 represent it as a numeric (floating point) value if that is possible
598 without loss of precision. Otherwise it will preserve the number as
599 a string value.
600
601 Numbers containing a fractional or exponential part will always be
602 represented as numeric (floating point) values, possibly at a loss
603 of precision.
604
605 This might create round-tripping problems as numbers might become
606 strings, but as Perl is typeless there is no other way to do it.
391 607
392 true, false 608 true, false
393 These JSON atoms become "JSON::XS::true" and "JSON::XS::false", 609 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
394 respectively. They are overloaded to act almost exactly like the 610 respectively. They are overloaded to act almost exactly like the
395 numbers 1 and 0. You can check wether a scalar is a JSON boolean by 611 numbers 1 and 0. You can check wether a scalar is a JSON boolean by
… …
427 643
428 to_json [\0,JSON::XS::true] # yields [false,true] 644 to_json [\0,JSON::XS::true] # yields [false,true]
429 645
430 JSON::XS::true, JSON::XS::false 646 JSON::XS::true, JSON::XS::false
431 These special values become JSON true and JSON false values, 647 These special values become JSON true and JSON false values,
432 respectively. You cna alos use "\1" and "\0" directly if you want. 648 respectively. You can also use "\1" and "\0" directly if you want.
433 649
434 blessed objects 650 blessed objects
435 Blessed objects are not allowed. JSON::XS currently tries to encode 651 Blessed objects are not allowed. JSON::XS currently tries to encode
436 their underlying representation (hash- or arrayref), but this 652 their underlying representation (hash- or arrayref), but this
437 behaviour might change in future versions. 653 behaviour might change in future versions.
… …
588 It shows the number of encodes/decodes per second (JSON::XS uses the 804 It shows the number of encodes/decodes per second (JSON::XS uses the
589 functional interface, while JSON::XS/2 uses the OO interface with 805 functional interface, while JSON::XS/2 uses the OO interface with
590 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). 806 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
591 Higher is better: 807 Higher is better:
592 808
809 Storable | 15779.925 | 14169.946 |
810 -----------+------------+------------+
593 module | encode | decode | 811 module | encode | decode |
594 -----------|------------|------------| 812 -----------|------------|------------|
595 JSON | 7645.468 | 4208.613 | 813 JSON | 4990.842 | 4088.813 |
596 JSON::DWIW | 40721.398 | 77101.176 | 814 JSON::DWIW | 51653.990 | 71575.154 |
597 JSON::PC | 65948.176 | 78251.940 | 815 JSON::PC | 65948.176 | 74631.744 |
598 JSON::Syck | 22844.793 | 26479.192 | 816 JSON::PP | 8931.652 | 3817.168 |
817 JSON::Syck | 24877.248 | 27776.848 |
599 JSON::XS | 388361.481 | 199728.762 | 818 JSON::XS | 388361.481 | 227951.304 |
600 JSON::XS/2 | 218453.333 | 192399.266 | 819 JSON::XS/2 | 227951.304 | 218453.333 |
601 JSON::XS/3 | 338250.323 | 192399.266 | 820 JSON::XS/3 | 338250.323 | 218453.333 |
602 Storable | 15779.925 | 14169.946 | 821 Storable | 16500.016 | 135300.129 |
603 -----------+------------+------------+ 822 -----------+------------+------------+
604 823
605 That is, JSON::XS is about five times faster than JSON::DWIW on 824 That is, JSON::XS is about five times faster than JSON::DWIW on
606 encoding, about three times faster on decoding, and over fourty times 825 encoding, about three times faster on decoding, and over fourty times
607 faster than JSON, even with pretty-printing and key sorting. It also 826 faster than JSON, even with pretty-printing and key sorting. It also
… …
610 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 829 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
611 search API (http://nanoref.com/yahooapis/mgPdGg): 830 search API (http://nanoref.com/yahooapis/mgPdGg):
612 831
613 module | encode | decode | 832 module | encode | decode |
614 -----------|------------|------------| 833 -----------|------------|------------|
615 JSON | 254.685 | 37.665 | 834 JSON | 55.260 | 34.971 |
616 JSON::DWIW | 843.343 | 1049.731 | 835 JSON::DWIW | 825.228 | 1082.513 |
617 JSON::PC | 3602.116 | 2307.352 | 836 JSON::PC | 3571.444 | 2394.829 |
837 JSON::PP | 210.987 | 32.574 |
618 JSON::Syck | 505.107 | 787.899 | 838 JSON::Syck | 552.551 | 787.544 |
619 JSON::XS | 5747.196 | 3690.220 | 839 JSON::XS | 5780.463 | 4854.519 |
620 JSON::XS/2 | 3968.121 | 3676.634 | 840 JSON::XS/2 | 3869.998 | 4798.975 |
621 JSON::XS/3 | 6105.246 | 3662.508 | 841 JSON::XS/3 | 5862.880 | 4798.975 |
622 Storable | 4417.337 | 5285.161 | 842 Storable | 4445.002 | 5235.027 |
623 -----------+------------+------------+ 843 -----------+------------+------------+
624 844
625 Again, JSON::XS leads by far (except for Storable which non-surprisingly 845 Again, JSON::XS leads by far (except for Storable which non-surprisingly
626 decodes faster). 846 decodes faster).
627 847
… …
642 Second, you need to avoid resource-starving attacks. That means you 862 Second, you need to avoid resource-starving attacks. That means you
643 should limit the size of JSON texts you accept, or make sure then when 863 should limit the size of JSON texts you accept, or make sure then when
644 your resources run out, thats just fine (e.g. by using a separate 864 your resources run out, thats just fine (e.g. by using a separate
645 process that can crash safely). The size of a JSON text in octets or 865 process that can crash safely). The size of a JSON text in octets or
646 characters is usually a good indication of the size of the resources 866 characters is usually a good indication of the size of the resources
647 required to decode it into a Perl structure. 867 required to decode it into a Perl structure. While JSON::XS can check
868 the size of the JSON text, it might be too late when you already have it
869 in memory, so you might want to check the size before you accept the
870 string.
648 871
649 Third, JSON::XS recurses using the C stack when decoding objects and 872 Third, JSON::XS recurses using the C stack when decoding objects and
650 arrays. The C stack is a limited resource: for instance, on my amd64 873 arrays. The C stack is a limited resource: for instance, on my amd64
651 machine with 8MB of stack size I can decode around 180k nested arrays 874 machine with 8MB of stack size I can decode around 180k nested arrays
652 but only 14k nested JSON objects (due to perl itself recursing deeply on 875 but only 14k nested JSON objects (due to perl itself recursing deeply on
… …
665 you are vulnerable to some common attack vectors (which really are 888 you are vulnerable to some common attack vectors (which really are
666 browser design bugs, but it is still you who will have to deal with it, 889 browser design bugs, but it is still you who will have to deal with it,
667 as major browser developers care only for features, not about doing 890 as major browser developers care only for features, not about doing
668 security right). 891 security right).
669 892
893THREADS
894 This module is *not* guarenteed to be thread safe and there are no plans
895 to change this until Perl gets thread support (as opposed to the
896 horribly slow so-called "threads" which are simply slow and bloated
897 process simulations - use fork, its *much* faster, cheaper, better).
898
899 (It might actually work, but you ahve ben warned).
900
670BUGS 901BUGS
671 While the goal of this module is to be correct, that unfortunately does 902 While the goal of this module is to be correct, that unfortunately does
672 not mean its bug-free, only that I think its design is bug-free. It is 903 not mean its bug-free, only that I think its design is bug-free. It is
673 still relatively early in its development. If you keep reporting bugs 904 still relatively early in its development. If you keep reporting bugs
674 they will be fixed swiftly, though. 905 they will be fixed swiftly, though.
675 906
907 Please refrain from using rt.cpan.org or any other bug reporting
908 service. I put the contact address into my modules for a reason.
909
676AUTHOR 910AUTHOR
677 Marc Lehmann <schmorp@schmorp.de> 911 Marc Lehmann <schmorp@schmorp.de>
678 http://home.schmorp.de/ 912 http://home.schmorp.de/
679 913

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