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Revision 1.14 by root, Sat Jun 23 23:50:03 2007 UTC vs.
Revision 1.18 by root, Tue Aug 28 02:06:06 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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244 240
245 Example, space_before and indent disabled, space_after enabled: 241 Example, space_before and indent disabled, space_after enabled:
246 242
247 {"key": "value"} 243 {"key": "value"}
248 244
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
249 $json = $json->canonical ([$enable]) 284 $json = $json->canonical ([$enable])
250 If $enable is true (or missing), then the "encode" method will 285 If $enable is true (or missing), then the "encode" method will
251 output JSON objects by sorting their keys. This is adding a 286 output JSON objects by sorting their keys. This is adding a
252 comparatively high overhead. 287 comparatively high overhead.
253 288
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277 Example, encode a Perl scalar as JSON value with enabled 312 Example, encode a Perl scalar as JSON value with enabled
278 "allow_nonref", resulting in an invalid JSON text: 313 "allow_nonref", resulting in an invalid JSON text:
279 314
280 JSON::XS->new->allow_nonref->encode ("Hello, World!") 315 JSON::XS->new->allow_nonref->encode ("Hello, World!")
281 => "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 }
282 427
283 $json = $json->shrink ([$enable]) 428 $json = $json->shrink ([$enable])
284 Perl usually over-allocates memory a bit when allocating space for 429 Perl usually over-allocates memory a bit when allocating space for
285 strings. This flag optionally resizes strings generated by either 430 strings. This flag optionally resizes strings generated by either
286 "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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319 crossed to reach a given character in a string. 464 crossed to reach a given character in a string.
320 465
321 Setting the maximum depth to one disallows any nesting, so that 466 Setting the maximum depth to one disallows any nesting, so that
322 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.
323 468
324 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
325 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).
326 487
327 See SECURITY CONSIDERATIONS, below, for more info on why this is 488 See SECURITY CONSIDERATIONS, below, for more info on why this is
328 useful. 489 useful.
329 490
330 $json_text = $json->encode ($perl_scalar) 491 $json_text = $json->encode ($perl_scalar)
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380 A JSON string becomes a string scalar in Perl - Unicode codepoints 541 A JSON string becomes a string scalar in Perl - Unicode codepoints
381 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,
382 so no manual decoding is necessary. 543 so no manual decoding is necessary.
383 544
384 number 545 number
385 A JSON number becomes either an integer or numeric (floating point) 546 A JSON number becomes either an integer, numeric (floating point) or
386 scalar in perl, depending on its range and any fractional parts. On 547 string scalar in perl, depending on its range and any fractional
387 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
388 all the conversion details, but an integer may take slightly less 549 Perl handles all the conversion details, but an integer may take
389 memory and might represent more values exactly than (floating point) 550 slightly less memory and might represent more values exactly than
390 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.
391 565
392 true, false 566 true, false
393 These JSON atoms become "JSON::XS::true" and "JSON::XS::false", 567 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
394 respectively. They are overloaded to act almost exactly like the 568 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 569 numbers 1 and 0. You can check wether a scalar is a JSON boolean by
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588 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
589 functional interface, while JSON::XS/2 uses the OO interface with 763 functional interface, while JSON::XS/2 uses the OO interface with
590 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). 764 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
591 Higher is better: 765 Higher is better:
592 766
767 Storable | 15779.925 | 14169.946 |
768 -----------+------------+------------+
593 module | encode | decode | 769 module | encode | decode |
594 -----------|------------|------------| 770 -----------|------------|------------|
595 JSON | 7645.468 | 4208.613 | 771 JSON | 4990.842 | 4088.813 |
596 JSON::DWIW | 40721.398 | 77101.176 | 772 JSON::DWIW | 51653.990 | 71575.154 |
597 JSON::PC | 65948.176 | 78251.940 | 773 JSON::PC | 65948.176 | 74631.744 |
598 JSON::Syck | 22844.793 | 26479.192 | 774 JSON::PP | 8931.652 | 3817.168 |
775 JSON::Syck | 24877.248 | 27776.848 |
599 JSON::XS | 388361.481 | 199728.762 | 776 JSON::XS | 388361.481 | 227951.304 |
600 JSON::XS/2 | 218453.333 | 192399.266 | 777 JSON::XS/2 | 227951.304 | 218453.333 |
601 JSON::XS/3 | 338250.323 | 192399.266 | 778 JSON::XS/3 | 338250.323 | 218453.333 |
602 Storable | 15779.925 | 14169.946 | 779 Storable | 16500.016 | 135300.129 |
603 -----------+------------+------------+ 780 -----------+------------+------------+
604 781
605 That is, JSON::XS is about five times faster than JSON::DWIW on 782 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 783 encoding, about three times faster on decoding, and over fourty times
607 faster than JSON, even with pretty-printing and key sorting. It also 784 faster than JSON, even with pretty-printing and key sorting. It also
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610 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 787 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
611 search API (http://nanoref.com/yahooapis/mgPdGg): 788 search API (http://nanoref.com/yahooapis/mgPdGg):
612 789
613 module | encode | decode | 790 module | encode | decode |
614 -----------|------------|------------| 791 -----------|------------|------------|
615 JSON | 254.685 | 37.665 | 792 JSON | 55.260 | 34.971 |
616 JSON::DWIW | 843.343 | 1049.731 | 793 JSON::DWIW | 825.228 | 1082.513 |
617 JSON::PC | 3602.116 | 2307.352 | 794 JSON::PC | 3571.444 | 2394.829 |
795 JSON::PP | 210.987 | 32.574 |
618 JSON::Syck | 505.107 | 787.899 | 796 JSON::Syck | 552.551 | 787.544 |
619 JSON::XS | 5747.196 | 3690.220 | 797 JSON::XS | 5780.463 | 4854.519 |
620 JSON::XS/2 | 3968.121 | 3676.634 | 798 JSON::XS/2 | 3869.998 | 4798.975 |
621 JSON::XS/3 | 6105.246 | 3662.508 | 799 JSON::XS/3 | 5862.880 | 4798.975 |
622 Storable | 4417.337 | 5285.161 | 800 Storable | 4445.002 | 5235.027 |
623 -----------+------------+------------+ 801 -----------+------------+------------+
624 802
625 Again, JSON::XS leads by far (except for Storable which non-surprisingly 803 Again, JSON::XS leads by far (except for Storable which non-surprisingly
626 decodes faster). 804 decodes faster).
627 805
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642 Second, you need to avoid resource-starving attacks. That means you 820 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 821 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 822 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 823 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 824 characters is usually a good indication of the size of the resources
647 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.
648 829
649 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
650 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
651 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
652 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

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