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Revision 1.12 by root, Wed Jun 6 18:17:13 2007 UTC vs.
Revision 1.15 by root, Mon Jul 2 08:06:48 2007 UTC

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7 # exported functions, they croak on error 7 # exported functions, they croak on error
8 # and expect/generate UTF-8 8 # and expect/generate UTF-8
9 9
10 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 10 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
11 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 11 $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 12
17 # OO-interface 13 # OO-interface
18 14
19 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 15 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
20 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 16 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
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91 This function call is functionally identical to: 87 This function call is functionally identical to:
92 88
93 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 89 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
94 90
95 except being faster. 91 except being faster.
92
93 $is_boolean = JSON::XS::is_bool $scalar
94 Returns true if the passed scalar represents either JSON::XS::true
95 or JSON::XS::false, two constants that act like 1 and 0,
96 respectively and are used to represent JSON "true" and "false"
97 values in Perl.
98
99 See MAPPING, below, for more information on how JSON values are
100 mapped to Perl.
96 101
97OBJECT-ORIENTED INTERFACE 102OBJECT-ORIENTED INTERFACE
98 The object oriented interface lets you configure your own encoding or 103 The object oriented interface lets you configure your own encoding or
99 decoding style, within the limits of supported formats. 104 decoding style, within the limits of supported formats.
100 105
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268 Example, encode a Perl scalar as JSON value with enabled 273 Example, encode a Perl scalar as JSON value with enabled
269 "allow_nonref", resulting in an invalid JSON text: 274 "allow_nonref", resulting in an invalid JSON text:
270 275
271 JSON::XS->new->allow_nonref->encode ("Hello, World!") 276 JSON::XS->new->allow_nonref->encode ("Hello, World!")
272 => "Hello, World!" 277 => "Hello, World!"
278
279 $json = $json->allow_blessed ([$enable])
280 If $enable is true (or missing), then the "encode" method will not
281 barf when it encounters a blessed reference. Instead, the value of
282 the convert_blessed option will decide wether "null"
283 ("convert_blessed" disabled or no "to_json" method found) or a
284 representation of the object ("convert_blessed" enabled and
285 "to_json" method found) is being encoded. Has no effect on "decode".
286
287 If $enable is false (the default), then "encode" will throw an
288 exception when it encounters a blessed object.
289
290 $json = $json->convert_blessed ([$enable])
291 If $enable is true (or missing), then "encode", upon encountering a
292 blessed object, will check for the availability of the "TO_JSON"
293 method on the object's class. If found, it will be called in scalar
294 context and the resulting scalar will be encoded instead of the
295 object. If no "TO_JSON" method is found, the value of
296 "allow_blessed" will decide what to do.
297
298 The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
299 returns other blessed objects, those will be handled in the same
300 way. "TO_JSON" must take care of not causing an endless recursion
301 cycle (== crash) in this case. The name of "TO_JSON" was chosen
302 because other methods called by the Perl core (== not by the user of
303 the object) are usually in upper case letters and to avoid
304 collisions with the "to_json" function.
305
306 This setting does not yet influence "decode" in any way, but in the
307 future, global hooks might get installed that influence "decode" and
308 are enabled by this setting.
309
310 If $enable is false, then the "allow_blessed" setting will decide
311 what to do when a blessed object is found.
312
313 $json = $json->filter_json_object ([$coderef->($hashref)])
314 When $coderef is specified, it will be called from "decode" each
315 time it decodes a JSON object. The only argument is a reference to
316 the newly-created hash. If the code references returns a single
317 scalar (which need not be a reference), this value (i.e. a copy of
318 that scalar to avoid aliasing) is inserted into the deserialised
319 data structure. If it returns an empty list (NOTE: *not* "undef",
320 which is a valid scalar), the original deserialised hash will be
321 inserted. This setting can slow down decoding considerably.
322
323 When $coderef is omitted or undefined, any existing callback will be
324 removed and "decode" will not change the deserialised hash in any
325 way.
326
327 Example, convert all JSON objects into the integer 5:
328
329 my $js = JSON::XS->new->filter_json_object (sub { 5 });
330 # returns [5]
331 $js->decode ('[{}]')
332 # throw an exception because allow_nonref is not enabled
333 # so a lone 5 is not allowed.
334 $js->decode ('{"a":1, "b":2}');
335
336 $json = $json->filter_json_single_key_object ($key [=>
337 $coderef->($value)])
338 Works remotely similar to "filter_json_object", but is only called
339 for JSON objects having a single key named $key.
340
341 This $coderef is called before the one specified via
342 "filter_json_object", if any. It gets passed the single value in the
343 JSON object. If it returns a single value, it will be inserted into
344 the data structure. If it returns nothing (not even "undef" but the
345 empty list), the callback from "filter_json_object" will be called
346 next, as if no single-key callback were specified.
347
348 If $coderef is omitted or undefined, the corresponding callback will
349 be disabled. There can only ever be one callback for a given key.
350
351 As this callback gets called less often then the
352 "filter_json_object" one, decoding speed will not usually suffer as
353 much. Therefore, single-key objects make excellent targets to
354 serialise Perl objects into, especially as single-key JSON objects
355 are as close to the type-tagged value concept as JSON gets (its
356 basically an ID/VALUE tuple). Of course, JSON does not support this
357 in any way, so you need to make sure your data never looks like a
358 serialised Perl hash.
359
360 Typical names for the single object key are "__class_whatever__", or
361 "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
362 things like "__class_md5sum(classname)__", to reduce the risk of
363 clashing with real hashes.
364
365 Example, decode JSON objects of the form "{ "__widget__" => <id> }"
366 into the corresponding $WIDGET{<id>} object:
367
368 # return whatever is in $WIDGET{5}:
369 JSON::XS
370 ->new
371 ->filter_json_single_key_object (__widget__ => sub {
372 $WIDGET{ $_[0] }
373 })
374 ->decode ('{"__widget__": 5')
375
376 # this can be used with a TO_JSON method in some "widget" class
377 # for serialisation to json:
378 sub WidgetBase::TO_JSON {
379 my ($self) = @_;
380
381 unless ($self->{id}) {
382 $self->{id} = ..get..some..id..;
383 $WIDGET{$self->{id}} = $self;
384 }
385
386 { __widget__ => $self->{id} }
387 }
273 388
274 $json = $json->shrink ([$enable]) 389 $json = $json->shrink ([$enable])
275 Perl usually over-allocates memory a bit when allocating space for 390 Perl usually over-allocates memory a bit when allocating space for
276 strings. This flag optionally resizes strings generated by either 391 strings. This flag optionally resizes strings generated by either
277 "encode" or "decode" to their minimum size possible. This can save 392 "encode" or "decode" to their minimum size possible. This can save
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310 crossed to reach a given character in a string. 425 crossed to reach a given character in a string.
311 426
312 Setting the maximum depth to one disallows any nesting, so that 427 Setting the maximum depth to one disallows any nesting, so that
313 ensures that the object is only a single hash/object or array. 428 ensures that the object is only a single hash/object or array.
314 429
315 The argument to "max_depth" will be rounded up to the next nearest 430 The argument to "max_depth" will be rounded up to the next highest
316 power of two. 431 power of two. If no argument is given, the highest possible setting
432 will be used, which is rarely useful.
433
434 See SECURITY CONSIDERATIONS, below, for more info on why this is
435 useful.
436
437 $json = $json->max_size ([$maximum_string_size])
438 Set the maximum length a JSON text may have (in bytes) where
439 decoding is being attempted. The default is 0, meaning no limit.
440 When "decode" is called on a string longer then this number of
441 characters it will not attempt to decode the string but throw an
442 exception. This setting has no effect on "encode" (yet).
443
444 The argument to "max_size" will be rounded up to the next highest
445 power of two (so may be more than requested). If no argument is
446 given, the limit check will be deactivated (same as when 0 is
447 specified).
317 448
318 See SECURITY CONSIDERATIONS, below, for more info on why this is 449 See SECURITY CONSIDERATIONS, below, for more info on why this is
319 useful. 450 useful.
320 451
321 $json_text = $json->encode ($perl_scalar) 452 $json_text = $json->encode ($perl_scalar)
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379 all the conversion details, but an integer may take slightly less 510 all the conversion details, but an integer may take slightly less
380 memory and might represent more values exactly than (floating point) 511 memory and might represent more values exactly than (floating point)
381 numbers. 512 numbers.
382 513
383 true, false 514 true, false
384 These JSON atoms become 0, 1, respectively. Information is lost in 515 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
385 this process. Future versions might represent those values 516 respectively. They are overloaded to act almost exactly like the
386 differently, but they will be guarenteed to act like these integers 517 numbers 1 and 0. You can check wether a scalar is a JSON boolean by
387 would normally in Perl. 518 using the "JSON::XS::is_bool" function.
388 519
389 null 520 null
390 A JSON null atom becomes "undef" in Perl. 521 A JSON null atom becomes "undef" in Perl.
391 522
392 PERL -> JSON 523 PERL -> JSON
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416 can also use "JSON::XS::false" and "JSON::XS::true" to improve 547 can also use "JSON::XS::false" and "JSON::XS::true" to improve
417 readability. 548 readability.
418 549
419 to_json [\0,JSON::XS::true] # yields [false,true] 550 to_json [\0,JSON::XS::true] # yields [false,true]
420 551
552 JSON::XS::true, JSON::XS::false
553 These special values become JSON true and JSON false values,
554 respectively. You cna alos use "\1" and "\0" directly if you want.
555
421 blessed objects 556 blessed objects
422 Blessed objects are not allowed. JSON::XS currently tries to encode 557 Blessed objects are not allowed. JSON::XS currently tries to encode
423 their underlying representation (hash- or arrayref), but this 558 their underlying representation (hash- or arrayref), but this
424 behaviour might change in future versions. 559 behaviour might change in future versions.
425 560
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535 Does not generate valid JSON texts (key strings are often unquoted, 670 Does not generate valid JSON texts (key strings are often unquoted,
536 empty keys result in nothing being output) 671 empty keys result in nothing being output)
537 672
538 Does not check input for validity. 673 Does not check input for validity.
539 674
675 JSON and YAML
676 You often hear that JSON is a subset (or a close subset) of YAML. This
677 is, however, a mass hysteria and very far from the truth. In general,
678 there is no way to configure JSON::XS to output a data structure as
679 valid YAML.
680
681 If you really must use JSON::XS to generate YAML, you should use this
682 algorithm (subject to change in future versions):
683
684 my $to_yaml = JSON::XS->new->utf8->space_after (1);
685 my $yaml = $to_yaml->encode ($ref) . "\n";
686
687 This will usually generate JSON texts that also parse as valid YAML.
688 Please note that YAML has hardcoded limits on (simple) object key
689 lengths that JSON doesn't have, so you should make sure that your hash
690 keys are noticably shorter than the 1024 characters YAML allows.
691
692 There might be other incompatibilities that I am not aware of. In
693 general you should not try to generate YAML with a JSON generator or
694 vice versa, or try to parse JSON with a YAML parser or vice versa:
695 chances are high that you will run into severe interoperability
696 problems.
697
540 SPEED 698 SPEED
541 It seems that JSON::XS is surprisingly fast, as shown in the following 699 It seems that JSON::XS is surprisingly fast, as shown in the following
542 tables. They have been generated with the help of the "eg/bench" program 700 tables. They have been generated with the help of the "eg/bench" program
543 in the JSON::XS distribution, to make it easy to compare on your own 701 in the JSON::XS distribution, to make it easy to compare on your own
544 system. 702 system.
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549 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 707 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
550 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 708 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
551 709
552 It shows the number of encodes/decodes per second (JSON::XS uses the 710 It shows the number of encodes/decodes per second (JSON::XS uses the
553 functional interface, while JSON::XS/2 uses the OO interface with 711 functional interface, while JSON::XS/2 uses the OO interface with
554 pretty-printing and hashkey sorting enabled). Higher is better: 712 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
713 Higher is better:
555 714
715 Storable | 15779.925 | 14169.946 |
716 -----------+------------+------------+
556 module | encode | decode | 717 module | encode | decode |
557 -----------|------------|------------| 718 -----------|------------|------------|
558 JSON | 7645.468 | 4208.613 | 719 JSON | 4990.842 | 4088.813 |
559 JSON::DWIW | 68534.379 | 79437.576 | 720 JSON::DWIW | 51653.990 | 71575.154 |
560 JSON::PC | 65948.176 | 78251.940 | 721 JSON::PC | 65948.176 | 74631.744 |
561 JSON::Syck | 23379.621 | 28416.694 | 722 JSON::PP | 8931.652 | 3817.168 |
723 JSON::Syck | 24877.248 | 27776.848 |
562 JSON::XS | 388361.481 | 199728.762 | 724 JSON::XS | 388361.481 | 227951.304 |
563 JSON::XS/2 | 218453.333 | 192399.266 | 725 JSON::XS/2 | 227951.304 | 218453.333 |
564 JSON::XS/3 | 338250.323 | 192399.266 | 726 JSON::XS/3 | 338250.323 | 218453.333 |
565 Storable | 15732.573 | 28571.553 | 727 Storable | 16500.016 | 135300.129 |
566 -----------+------------+------------+ 728 -----------+------------+------------+
567 729
568 That is, JSON::XS is about five times faster than JSON::DWIW on 730 That is, JSON::XS is about five times faster than JSON::DWIW on
569 encoding, about three times faster on decoding, and over fourty times 731 encoding, about three times faster on decoding, and over fourty times
570 faster than JSON, even with pretty-printing and key sorting. It also 732 faster than JSON, even with pretty-printing and key sorting. It also
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573 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 735 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
574 search API (http://nanoref.com/yahooapis/mgPdGg): 736 search API (http://nanoref.com/yahooapis/mgPdGg):
575 737
576 module | encode | decode | 738 module | encode | decode |
577 -----------|------------|------------| 739 -----------|------------|------------|
578 JSON | 254.685 | 37.665 | 740 JSON | 55.260 | 34.971 |
579 JSON::DWIW | 1014.244 | 1087.678 | 741 JSON::DWIW | 825.228 | 1082.513 |
580 JSON::PC | 3602.116 | 2307.352 | 742 JSON::PC | 3571.444 | 2394.829 |
581 JSON::Syck | 558.035 | 776.263 | 743 JSON::PP | 210.987 | 32.574 |
582 JSON::XS | 5747.196 | 3543.684 | 744 JSON::Syck | 552.551 | 787.544 |
583 JSON::XS/2 | 3968.121 | 3589.170 | 745 JSON::XS | 5780.463 | 4854.519 |
584 JSON::XS/3 | 6105.246 | 3561.134 | 746 JSON::XS/2 | 3869.998 | 4798.975 |
585 Storable | 4456.337 | 5320.020 | 747 JSON::XS/3 | 5862.880 | 4798.975 |
748 Storable | 4445.002 | 5235.027 |
586 -----------+------------+------------+ 749 -----------+------------+------------+
587 750
588 Again, JSON::XS leads by far. 751 Again, JSON::XS leads by far (except for Storable which non-surprisingly
752 decodes faster).
589 753
590 On large strings containing lots of high unicode characters, some 754 On large strings containing lots of high unicode characters, some
591 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the 755 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
592 result will be broken due to missing (or wrong) unicode handling. Others 756 result will be broken due to missing (or wrong) unicode handling. Others
593 refuse to decode or encode properly, so it was impossible to prepare a 757 refuse to decode or encode properly, so it was impossible to prepare a
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604 Second, you need to avoid resource-starving attacks. That means you 768 Second, you need to avoid resource-starving attacks. That means you
605 should limit the size of JSON texts you accept, or make sure then when 769 should limit the size of JSON texts you accept, or make sure then when
606 your resources run out, thats just fine (e.g. by using a separate 770 your resources run out, thats just fine (e.g. by using a separate
607 process that can crash safely). The size of a JSON text in octets or 771 process that can crash safely). The size of a JSON text in octets or
608 characters is usually a good indication of the size of the resources 772 characters is usually a good indication of the size of the resources
609 required to decode it into a Perl structure. 773 required to decode it into a Perl structure. While JSON::XS can check
774 the size of the JSON text, it might be too late when you already have it
775 in memory, so you might want to check the size before you accept the
776 string.
610 777
611 Third, JSON::XS recurses using the C stack when decoding objects and 778 Third, JSON::XS recurses using the C stack when decoding objects and
612 arrays. The C stack is a limited resource: for instance, on my amd64 779 arrays. The C stack is a limited resource: for instance, on my amd64
613 machine with 8MB of stack size I can decode around 180k nested arrays 780 machine with 8MB of stack size I can decode around 180k nested arrays
614 but only 14k nested JSON objects (due to perl itself recursing deeply on 781 but only 14k nested JSON objects (due to perl itself recursing deeply on
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619 786
620 And last but least, something else could bomb you that I forgot to think 787 And last but least, something else could bomb you that I forgot to think
621 of. In that case, you get to keep the pieces. I am always open for 788 of. In that case, you get to keep the pieces. I am always open for
622 hints, though... 789 hints, though...
623 790
791 If you are using JSON::XS to return packets to consumption by javascript
792 scripts in a browser you should have a look at
793 <http://jpsykes.com/47/practical-csrf-and-json-security> to see wether
794 you are vulnerable to some common attack vectors (which really are
795 browser design bugs, but it is still you who will have to deal with it,
796 as major browser developers care only for features, not about doing
797 security right).
798
624BUGS 799BUGS
625 While the goal of this module is to be correct, that unfortunately does 800 While the goal of this module is to be correct, that unfortunately does
626 not mean its bug-free, only that I think its design is bug-free. It is 801 not mean its bug-free, only that I think its design is bug-free. It is
627 still relatively early in its development. If you keep reporting bugs 802 still relatively early in its development. If you keep reporting bugs
628 they will be fixed swiftly, though. 803 they will be fixed swiftly, though.

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