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Revision 1.11 by root, Wed May 9 16:35:21 2007 UTC vs.
Revision 1.18 by root, Tue Aug 28 02:06:06 2007 UTC

… …
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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235 240
236 Example, space_before and indent disabled, space_after enabled: 241 Example, space_before and indent disabled, space_after enabled:
237 242
238 {"key": "value"} 243 {"key": "value"}
239 244
245 $json = $json->relaxed ([$enable])
246 If $enable is true (or missing), then "decode" will accept some
247 extensions to normal JSON syntax (see below). "encode" will not be
248 affected in anyway. *Be aware that this option makes you accept
249 invalid JSON texts as if they were valid!*. I suggest only to use
250 this option to parse application-specific files written by humans
251 (configuration files, resource files etc.)
252
253 If $enable is false (the default), then "decode" will only accept
254 valid JSON texts.
255
256 Currently accepted extensions are:
257
258 * list items can have an end-comma
259 JSON *separates* array elements and key-value pairs with commas.
260 This can be annoying if you write JSON texts manually and want
261 to be able to quickly append elements, so this extension accepts
262 comma at the end of such items not just between them:
263
264 [
265 1,
266 2, <- this comma not normally allowed
267 ]
268 {
269 "k1": "v1",
270 "k2": "v2", <- this comma not normally allowed
271 }
272
273 * shell-style '#'-comments
274 Whenever JSON allows whitespace, shell-style comments are
275 additionally allowed. They are terminated by the first
276 carriage-return or line-feed character, after which more
277 white-space and comments are allowed.
278
279 [
280 1, # this comment not allowed in JSON
281 # neither this one...
282 ]
283
240 $json = $json->canonical ([$enable]) 284 $json = $json->canonical ([$enable])
241 If $enable is true (or missing), then the "encode" method will 285 If $enable is true (or missing), then the "encode" method will
242 output JSON objects by sorting their keys. This is adding a 286 output JSON objects by sorting their keys. This is adding a
243 comparatively high overhead. 287 comparatively high overhead.
244 288
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268 Example, encode a Perl scalar as JSON value with enabled 312 Example, encode a Perl scalar as JSON value with enabled
269 "allow_nonref", resulting in an invalid JSON text: 313 "allow_nonref", resulting in an invalid JSON text:
270 314
271 JSON::XS->new->allow_nonref->encode ("Hello, World!") 315 JSON::XS->new->allow_nonref->encode ("Hello, World!")
272 => "Hello, World!" 316 => "Hello, World!"
317
318 $json = $json->allow_blessed ([$enable])
319 If $enable is true (or missing), then the "encode" method will not
320 barf when it encounters a blessed reference. Instead, the value of
321 the convert_blessed option will decide wether "null"
322 ("convert_blessed" disabled or no "to_json" method found) or a
323 representation of the object ("convert_blessed" enabled and
324 "to_json" method found) is being encoded. Has no effect on "decode".
325
326 If $enable is false (the default), then "encode" will throw an
327 exception when it encounters a blessed object.
328
329 $json = $json->convert_blessed ([$enable])
330 If $enable is true (or missing), then "encode", upon encountering a
331 blessed object, will check for the availability of the "TO_JSON"
332 method on the object's class. If found, it will be called in scalar
333 context and the resulting scalar will be encoded instead of the
334 object. If no "TO_JSON" method is found, the value of
335 "allow_blessed" will decide what to do.
336
337 The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
338 returns other blessed objects, those will be handled in the same
339 way. "TO_JSON" must take care of not causing an endless recursion
340 cycle (== crash) in this case. The name of "TO_JSON" was chosen
341 because other methods called by the Perl core (== not by the user of
342 the object) are usually in upper case letters and to avoid
343 collisions with the "to_json" function.
344
345 This setting does not yet influence "decode" in any way, but in the
346 future, global hooks might get installed that influence "decode" and
347 are enabled by this setting.
348
349 If $enable is false, then the "allow_blessed" setting will decide
350 what to do when a blessed object is found.
351
352 $json = $json->filter_json_object ([$coderef->($hashref)])
353 When $coderef is specified, it will be called from "decode" each
354 time it decodes a JSON object. The only argument is a reference to
355 the newly-created hash. If the code references returns a single
356 scalar (which need not be a reference), this value (i.e. a copy of
357 that scalar to avoid aliasing) is inserted into the deserialised
358 data structure. If it returns an empty list (NOTE: *not* "undef",
359 which is a valid scalar), the original deserialised hash will be
360 inserted. This setting can slow down decoding considerably.
361
362 When $coderef is omitted or undefined, any existing callback will be
363 removed and "decode" will not change the deserialised hash in any
364 way.
365
366 Example, convert all JSON objects into the integer 5:
367
368 my $js = JSON::XS->new->filter_json_object (sub { 5 });
369 # returns [5]
370 $js->decode ('[{}]')
371 # throw an exception because allow_nonref is not enabled
372 # so a lone 5 is not allowed.
373 $js->decode ('{"a":1, "b":2}');
374
375 $json = $json->filter_json_single_key_object ($key [=>
376 $coderef->($value)])
377 Works remotely similar to "filter_json_object", but is only called
378 for JSON objects having a single key named $key.
379
380 This $coderef is called before the one specified via
381 "filter_json_object", if any. It gets passed the single value in the
382 JSON object. If it returns a single value, it will be inserted into
383 the data structure. If it returns nothing (not even "undef" but the
384 empty list), the callback from "filter_json_object" will be called
385 next, as if no single-key callback were specified.
386
387 If $coderef is omitted or undefined, the corresponding callback will
388 be disabled. There can only ever be one callback for a given key.
389
390 As this callback gets called less often then the
391 "filter_json_object" one, decoding speed will not usually suffer as
392 much. Therefore, single-key objects make excellent targets to
393 serialise Perl objects into, especially as single-key JSON objects
394 are as close to the type-tagged value concept as JSON gets (its
395 basically an ID/VALUE tuple). Of course, JSON does not support this
396 in any way, so you need to make sure your data never looks like a
397 serialised Perl hash.
398
399 Typical names for the single object key are "__class_whatever__", or
400 "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
401 things like "__class_md5sum(classname)__", to reduce the risk of
402 clashing with real hashes.
403
404 Example, decode JSON objects of the form "{ "__widget__" => <id> }"
405 into the corresponding $WIDGET{<id>} object:
406
407 # return whatever is in $WIDGET{5}:
408 JSON::XS
409 ->new
410 ->filter_json_single_key_object (__widget__ => sub {
411 $WIDGET{ $_[0] }
412 })
413 ->decode ('{"__widget__": 5')
414
415 # this can be used with a TO_JSON method in some "widget" class
416 # for serialisation to json:
417 sub WidgetBase::TO_JSON {
418 my ($self) = @_;
419
420 unless ($self->{id}) {
421 $self->{id} = ..get..some..id..;
422 $WIDGET{$self->{id}} = $self;
423 }
424
425 { __widget__ => $self->{id} }
426 }
273 427
274 $json = $json->shrink ([$enable]) 428 $json = $json->shrink ([$enable])
275 Perl usually over-allocates memory a bit when allocating space for 429 Perl usually over-allocates memory a bit when allocating space for
276 strings. This flag optionally resizes strings generated by either 430 strings. This flag optionally resizes strings generated by either
277 "encode" or "decode" to their minimum size possible. This can save 431 "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. 464 crossed to reach a given character in a string.
311 465
312 Setting the maximum depth to one disallows any nesting, so that 466 Setting the maximum depth to one disallows any nesting, so that
313 ensures that the object is only a single hash/object or array. 467 ensures that the object is only a single hash/object or array.
314 468
315 The argument to "max_depth" will be rounded up to the next nearest 469 The argument to "max_depth" will be rounded up to the next highest
316 power of two. 470 power of two. If no argument is given, the highest possible setting
471 will be used, which is rarely useful.
472
473 See SECURITY CONSIDERATIONS, below, for more info on why this is
474 useful.
475
476 $json = $json->max_size ([$maximum_string_size])
477 Set the maximum length a JSON text may have (in bytes) where
478 decoding is being attempted. The default is 0, meaning no limit.
479 When "decode" is called on a string longer then this number of
480 characters it will not attempt to decode the string but throw an
481 exception. This setting has no effect on "encode" (yet).
482
483 The argument to "max_size" will be rounded up to the next highest
484 power of two (so may be more than requested). If no argument is
485 given, the limit check will be deactivated (same as when 0 is
486 specified).
317 487
318 See SECURITY CONSIDERATIONS, below, for more info on why this is 488 See SECURITY CONSIDERATIONS, below, for more info on why this is
319 useful. 489 useful.
320 490
321 $json_text = $json->encode ($perl_scalar) 491 $json_text = $json->encode ($perl_scalar)
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371 A JSON string becomes a string scalar in Perl - Unicode codepoints 541 A JSON string becomes a string scalar in Perl - Unicode codepoints
372 in JSON are represented by the same codepoints in the Perl string, 542 in JSON are represented by the same codepoints in the Perl string,
373 so no manual decoding is necessary. 543 so no manual decoding is necessary.
374 544
375 number 545 number
376 A JSON number becomes either an integer or numeric (floating point) 546 A JSON number becomes either an integer, numeric (floating point) or
377 scalar in perl, depending on its range and any fractional parts. On 547 string scalar in perl, depending on its range and any fractional
378 the Perl level, there is no difference between those as Perl handles 548 parts. On the Perl level, there is no difference between those as
379 all the conversion details, but an integer may take slightly less 549 Perl handles all the conversion details, but an integer may take
380 memory and might represent more values exactly than (floating point) 550 slightly less memory and might represent more values exactly than
381 numbers. 551 (floating point) numbers.
552
553 If the number consists of digits only, JSON::XS will try to
554 represent it as an integer value. If that fails, it will try to
555 represent it as a numeric (floating point) value if that is possible
556 without loss of precision. Otherwise it will preserve the number as
557 a string value.
558
559 Numbers containing a fractional or exponential part will always be
560 represented as numeric (floating point) values, possibly at a loss
561 of precision.
562
563 This might create round-tripping problems as numbers might become
564 strings, but as Perl is typeless there is no other way to do it.
382 565
383 true, false 566 true, false
384 These JSON atoms become 0, 1, respectively. Information is lost in 567 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
385 this process. Future versions might represent those values 568 respectively. They are overloaded to act almost exactly like the
386 differently, but they will be guarenteed to act like these integers 569 numbers 1 and 0. You can check wether a scalar is a JSON boolean by
387 would normally in Perl. 570 using the "JSON::XS::is_bool" function.
388 571
389 null 572 null
390 A JSON null atom becomes "undef" in Perl. 573 A JSON null atom becomes "undef" in Perl.
391 574
392 PERL -> JSON 575 PERL -> JSON
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416 can also use "JSON::XS::false" and "JSON::XS::true" to improve 599 can also use "JSON::XS::false" and "JSON::XS::true" to improve
417 readability. 600 readability.
418 601
419 to_json [\0,JSON::XS::true] # yields [false,true] 602 to_json [\0,JSON::XS::true] # yields [false,true]
420 603
604 JSON::XS::true, JSON::XS::false
605 These special values become JSON true and JSON false values,
606 respectively. You cna alos use "\1" and "\0" directly if you want.
607
421 blessed objects 608 blessed objects
422 Blessed objects are not allowed. JSON::XS currently tries to encode 609 Blessed objects are not allowed. JSON::XS currently tries to encode
423 their underlying representation (hash- or arrayref), but this 610 their underlying representation (hash- or arrayref), but this
424 behaviour might change in future versions. 611 behaviour might change in future versions.
425 612
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535 Does not generate valid JSON texts (key strings are often unquoted, 722 Does not generate valid JSON texts (key strings are often unquoted,
536 empty keys result in nothing being output) 723 empty keys result in nothing being output)
537 724
538 Does not check input for validity. 725 Does not check input for validity.
539 726
727 JSON and YAML
728 You often hear that JSON is a subset (or a close subset) of YAML. This
729 is, however, a mass hysteria and very far from the truth. In general,
730 there is no way to configure JSON::XS to output a data structure as
731 valid YAML.
732
733 If you really must use JSON::XS to generate YAML, you should use this
734 algorithm (subject to change in future versions):
735
736 my $to_yaml = JSON::XS->new->utf8->space_after (1);
737 my $yaml = $to_yaml->encode ($ref) . "\n";
738
739 This will usually generate JSON texts that also parse as valid YAML.
740 Please note that YAML has hardcoded limits on (simple) object key
741 lengths that JSON doesn't have, so you should make sure that your hash
742 keys are noticably shorter than the 1024 characters YAML allows.
743
744 There might be other incompatibilities that I am not aware of. In
745 general you should not try to generate YAML with a JSON generator or
746 vice versa, or try to parse JSON with a YAML parser or vice versa:
747 chances are high that you will run into severe interoperability
748 problems.
749
540 SPEED 750 SPEED
541 It seems that JSON::XS is surprisingly fast, as shown in the following 751 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 752 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 753 in the JSON::XS distribution, to make it easy to compare on your own
544 system. 754 system.
545 755
546 First comes a comparison between various modules using a very short JSON 756 First comes a comparison between various modules using a very short
547 string: 757 single-line JSON string:
548 758
549 {"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null} 759 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
760 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
550 761
551 It shows the number of encodes/decodes per second (JSON::XS uses the 762 It shows the number of encodes/decodes per second (JSON::XS uses the
552 functional interface, while JSON::XS/2 uses the OO interface with 763 functional interface, while JSON::XS/2 uses the OO interface with
553 pretty-printing and hashkey sorting enabled). Higher is better: 764 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
765 Higher is better:
554 766
767 Storable | 15779.925 | 14169.946 |
768 -----------+------------+------------+
555 module | encode | decode | 769 module | encode | decode |
556 -----------|------------|------------| 770 -----------|------------|------------|
557 JSON | 11488.516 | 7823.035 | 771 JSON | 4990.842 | 4088.813 |
558 JSON::DWIW | 94708.054 | 129094.260 | 772 JSON::DWIW | 51653.990 | 71575.154 |
559 JSON::PC | 63884.157 | 128528.212 | 773 JSON::PC | 65948.176 | 74631.744 |
774 JSON::PP | 8931.652 | 3817.168 |
560 JSON::Syck | 34898.677 | 42096.911 | 775 JSON::Syck | 24877.248 | 27776.848 |
561 JSON::XS | 654027.064 | 396423.669 | 776 JSON::XS | 388361.481 | 227951.304 |
562 JSON::XS/2 | 371564.190 | 371725.613 | 777 JSON::XS/2 | 227951.304 | 218453.333 |
778 JSON::XS/3 | 338250.323 | 218453.333 |
779 Storable | 16500.016 | 135300.129 |
563 -----------+------------+------------+ 780 -----------+------------+------------+
564 781
565 That is, JSON::XS is more than six times faster than JSON::DWIW on 782 That is, JSON::XS is about five times faster than JSON::DWIW on
566 encoding, more than three times faster on decoding, and about thirty 783 encoding, about three times faster on decoding, and over fourty times
567 times faster than JSON, even with pretty-printing and key sorting. 784 faster than JSON, even with pretty-printing and key sorting. It also
785 compares favourably to Storable for small amounts of data.
568 786
569 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 787 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
570 search API (http://nanoref.com/yahooapis/mgPdGg): 788 search API (http://nanoref.com/yahooapis/mgPdGg):
571 789
572 module | encode | decode | 790 module | encode | decode |
573 -----------|------------|------------| 791 -----------|------------|------------|
574 JSON | 273.023 | 44.674 | 792 JSON | 55.260 | 34.971 |
575 JSON::DWIW | 1089.383 | 1145.704 | 793 JSON::DWIW | 825.228 | 1082.513 |
576 JSON::PC | 3097.419 | 2393.921 | 794 JSON::PC | 3571.444 | 2394.829 |
577 JSON::Syck | 514.060 | 843.053 | 795 JSON::PP | 210.987 | 32.574 |
578 JSON::XS | 6479.668 | 3636.364 | 796 JSON::Syck | 552.551 | 787.544 |
579 JSON::XS/2 | 3774.221 | 3599.124 | 797 JSON::XS | 5780.463 | 4854.519 |
798 JSON::XS/2 | 3869.998 | 4798.975 |
799 JSON::XS/3 | 5862.880 | 4798.975 |
800 Storable | 4445.002 | 5235.027 |
580 -----------+------------+------------+ 801 -----------+------------+------------+
581 802
582 Again, JSON::XS leads by far. 803 Again, JSON::XS leads by far (except for Storable which non-surprisingly
804 decodes faster).
583 805
584 On large strings containing lots of high unicode characters, some 806 On large strings containing lots of high unicode characters, some
585 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the 807 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
586 result will be broken due to missing (or wrong) unicode handling. Others 808 result will be broken due to missing (or wrong) unicode handling. Others
587 refuse to decode or encode properly, so it was impossible to prepare a 809 refuse to decode or encode properly, so it was impossible to prepare a
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598 Second, you need to avoid resource-starving attacks. That means you 820 Second, you need to avoid resource-starving attacks. That means you
599 should limit the size of JSON texts you accept, or make sure then when 821 should limit the size of JSON texts you accept, or make sure then when
600 your resources run out, thats just fine (e.g. by using a separate 822 your resources run out, thats just fine (e.g. by using a separate
601 process that can crash safely). The size of a JSON text in octets or 823 process that can crash safely). The size of a JSON text in octets or
602 characters is usually a good indication of the size of the resources 824 characters is usually a good indication of the size of the resources
603 required to decode it into a Perl structure. 825 required to decode it into a Perl structure. While JSON::XS can check
826 the size of the JSON text, it might be too late when you already have it
827 in memory, so you might want to check the size before you accept the
828 string.
604 829
605 Third, JSON::XS recurses using the C stack when decoding objects and 830 Third, JSON::XS recurses using the C stack when decoding objects and
606 arrays. The C stack is a limited resource: for instance, on my amd64 831 arrays. The C stack is a limited resource: for instance, on my amd64
607 machine with 8MB of stack size I can decode around 180k nested arrays 832 machine with 8MB of stack size I can decode around 180k nested arrays
608 but only 14k nested JSON objects (due to perl itself recursing deeply on 833 but only 14k nested JSON objects (due to perl itself recursing deeply on
… …
613 838
614 And last but least, something else could bomb you that I forgot to think 839 And last but least, something else could bomb you that I forgot to think
615 of. In that case, you get to keep the pieces. I am always open for 840 of. In that case, you get to keep the pieces. I am always open for
616 hints, though... 841 hints, though...
617 842
843 If you are using JSON::XS to return packets to consumption by javascript
844 scripts in a browser you should have a look at
845 <http://jpsykes.com/47/practical-csrf-and-json-security> to see wether
846 you are vulnerable to some common attack vectors (which really are
847 browser design bugs, but it is still you who will have to deal with it,
848 as major browser developers care only for features, not about doing
849 security right).
850
618BUGS 851BUGS
619 While the goal of this module is to be correct, that unfortunately does 852 While the goal of this module is to be correct, that unfortunately does
620 not mean its bug-free, only that I think its design is bug-free. It is 853 not mean its bug-free, only that I think its design is bug-free. It is
621 still relatively early in its development. If you keep reporting bugs 854 still relatively early in its development. If you keep reporting bugs
622 they will be fixed swiftly, though. 855 they will be fixed swiftly, though.

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