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Revision 1.21 by root, Sun Mar 25 02:32:40 2007 UTC vs.
Revision 1.43 by root, Sat Jun 23 23:49:29 2007 UTC

4 4
5=head1 SYNOPSIS 5=head1 SYNOPSIS
6 6
7 use JSON::XS; 7 use JSON::XS;
8 8
9 # exported functions, croak on error 9 # exported functions, they croak on error
10 # and expect/generate UTF-8
10 11
11 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 12 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
12 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 13 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text;
13 14
14 # objToJson and jsonToObj are exported for JSON 15 # objToJson and jsonToObj aliases to to_json and from_json
16 # are exported for compatibility to the JSON module,
15 # compatibility, but should not be used in new code. 17 # but should not be used in new code.
16 18
17 # oo-interface 19 # OO-interface
18 20
19 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 21 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
20 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 22 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
21 $perl_scalar = $coder->decode ($unicode_json_text); 23 $perl_scalar = $coder->decode ($unicode_json_text);
22 24
83 85
84package JSON::XS; 86package JSON::XS;
85 87
86use strict; 88use strict;
87 89
88BEGIN {
89 our $VERSION = '0.8'; 90our $VERSION = '1.3';
90 our @ISA = qw(Exporter); 91our @ISA = qw(Exporter);
91 92
92 our @EXPORT = qw(to_json from_json objToJson jsonToObj); 93our @EXPORT = qw(to_json from_json objToJson jsonToObj);
93 require Exporter;
94 94
95 require XSLoader; 95use Exporter;
96 XSLoader::load JSON::XS::, $VERSION; 96use XSLoader;
97}
98 97
99=head1 FUNCTIONAL INTERFACE 98=head1 FUNCTIONAL INTERFACE
100 99
101The following convinience methods are provided by this module. They are 100The following convinience methods are provided by this module. They are
102exported by default: 101exported by default:
125 124
126 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 125 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
127 126
128except being faster. 127except being faster.
129 128
129=item $is_boolean = JSON::XS::is_bool $scalar
130
131Returns true if the passed scalar represents either JSON::XS::true or
132JSON::XS::false, two constants that act like C<1> and C<0>, respectively
133and are used to represent JSON C<true> and C<false> values in Perl.
134
135See MAPPING, below, for more information on how JSON values are mapped to
136Perl.
137
130=back 138=back
139
131 140
132=head1 OBJECT-ORIENTED INTERFACE 141=head1 OBJECT-ORIENTED INTERFACE
133 142
134The object oriented interface lets you configure your own encoding or 143The object oriented interface lets you configure your own encoding or
135decoding style, within the limits of supported formats. 144decoding style, within the limits of supported formats.
151 160
152If C<$enable> is true (or missing), then the C<encode> method will not 161If C<$enable> is true (or missing), then the C<encode> method will not
153generate characters outside the code range C<0..127> (which is ASCII). Any 162generate characters outside the code range C<0..127> (which is ASCII). Any
154unicode characters outside that range will be escaped using either a 163unicode characters outside that range will be escaped using either a
155single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, 164single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
156as per RFC4627. 165as per RFC4627. The resulting encoded JSON text can be treated as a native
166unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
167or any other superset of ASCII.
157 168
158If C<$enable> is false, then the C<encode> method will not escape Unicode 169If C<$enable> is false, then the C<encode> method will not escape Unicode
159characters unless required by the JSON syntax. This results in a faster 170characters unless required by the JSON syntax or other flags. This results
160and more compact format. 171in a faster and more compact format.
172
173The main use for this flag is to produce JSON texts that can be
174transmitted over a 7-bit channel, as the encoded JSON texts will not
175contain any 8 bit characters.
161 176
162 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 177 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
163 => ["\ud801\udc01"] 178 => ["\ud801\udc01"]
179
180=item $json = $json->latin1 ([$enable])
181
182If C<$enable> is true (or missing), then the C<encode> method will encode
183the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
184outside the code range C<0..255>. The resulting string can be treated as a
185latin1-encoded JSON text or a native unicode string. The C<decode> method
186will not be affected in any way by this flag, as C<decode> by default
187expects unicode, which is a strict superset of latin1.
188
189If C<$enable> is false, then the C<encode> method will not escape Unicode
190characters unless required by the JSON syntax or other flags.
191
192The main use for this flag is efficiently encoding binary data as JSON
193text, as most octets will not be escaped, resulting in a smaller encoded
194size. The disadvantage is that the resulting JSON text is encoded
195in latin1 (and must correctly be treated as such when storing and
196transfering), a rare encoding for JSON. It is therefore most useful when
197you want to store data structures known to contain binary data efficiently
198in files or databases, not when talking to other JSON encoders/decoders.
199
200 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
201 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
164 202
165=item $json = $json->utf8 ([$enable]) 203=item $json = $json->utf8 ([$enable])
166 204
167If C<$enable> is true (or missing), then the C<encode> method will encode 205If C<$enable> is true (or missing), then the C<encode> method will encode
168the JSON result into UTF-8, as required by many protocols, while the 206the JSON result into UTF-8, as required by many protocols, while the
281 => "Hello, World!" 319 => "Hello, World!"
282 320
283=item $json = $json->shrink ([$enable]) 321=item $json = $json->shrink ([$enable])
284 322
285Perl usually over-allocates memory a bit when allocating space for 323Perl usually over-allocates memory a bit when allocating space for
286strings. This flag optionally resizes strings generated by either 324strings. This flag optionally resizes strings generated by either
287C<encode> or C<decode> to their minimum size possible. This can save 325C<encode> or C<decode> to their minimum size possible. This can save
288memory when your JSON texts are either very very long or you have many 326memory when your JSON texts are either very very long or you have many
289short strings. It will also try to downgrade any strings to octet-form 327short strings. It will also try to downgrade any strings to octet-form
290if possible: perl stores strings internally either in an encoding called 328if possible: perl stores strings internally either in an encoding called
291UTF-X or in octet-form. The latter cannot store everything but uses less 329UTF-X or in octet-form. The latter cannot store everything but uses less
292space in general. 330space in general (and some buggy Perl or C code might even rely on that
331internal representation being used).
293 332
333The actual definition of what shrink does might change in future versions,
334but it will always try to save space at the expense of time.
335
294If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit, 336If C<$enable> is true (or missing), the string returned by C<encode> will
295while all strings generated by C<decode> will also be shrunk-to-fit. 337be shrunk-to-fit, while all strings generated by C<decode> will also be
338shrunk-to-fit.
296 339
297If C<$enable> is false, then the normal perl allocation algorithms are used. 340If C<$enable> is false, then the normal perl allocation algorithms are used.
298If you work with your data, then this is likely to be faster. 341If you work with your data, then this is likely to be faster.
299 342
300In the future, this setting might control other things, such as converting 343In the future, this setting might control other things, such as converting
301strings that look like integers or floats into integers or floats 344strings that look like integers or floats into integers or floats
302internally (there is no difference on the Perl level), saving space. 345internally (there is no difference on the Perl level), saving space.
346
347=item $json = $json->max_depth ([$maximum_nesting_depth])
348
349Sets the maximum nesting level (default C<512>) accepted while encoding
350or decoding. If the JSON text or Perl data structure has an equal or
351higher nesting level then this limit, then the encoder and decoder will
352stop and croak at that point.
353
354Nesting level is defined by number of hash- or arrayrefs that the encoder
355needs to traverse to reach a given point or the number of C<{> or C<[>
356characters without their matching closing parenthesis crossed to reach a
357given character in a string.
358
359Setting the maximum depth to one disallows any nesting, so that ensures
360that the object is only a single hash/object or array.
361
362The argument to C<max_depth> will be rounded up to the next nearest power
363of two.
364
365See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
303 366
304=item $json_text = $json->encode ($perl_scalar) 367=item $json_text = $json->encode ($perl_scalar)
305 368
306Converts the given Perl data structure (a simple scalar or a reference 369Converts the given Perl data structure (a simple scalar or a reference
307to a hash or array) to its JSON representation. Simple scalars will be 370to a hash or array) to its JSON representation. Simple scalars will be
317 380
318JSON numbers and strings become simple Perl scalars. JSON arrays become 381JSON numbers and strings become simple Perl scalars. JSON arrays become
319Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes 382Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
320C<1>, C<false> becomes C<0> and C<null> becomes C<undef>. 383C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
321 384
385=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
386
387This works like the C<decode> method, but instead of raising an exception
388when there is trailing garbage after the first JSON object, it will
389silently stop parsing there and return the number of characters consumed
390so far.
391
392This is useful if your JSON texts are not delimited by an outer protocol
393(which is not the brightest thing to do in the first place) and you need
394to know where the JSON text ends.
395
396 JSON::XS->new->decode_prefix ("[1] the tail")
397 => ([], 3)
398
322=back 399=back
400
323 401
324=head1 MAPPING 402=head1 MAPPING
325 403
326This section describes how JSON::XS maps Perl values to JSON values and 404This section describes how JSON::XS maps Perl values to JSON values and
327vice versa. These mappings are designed to "do the right thing" in most 405vice versa. These mappings are designed to "do the right thing" in most
329(what you put in comes out as something equivalent). 407(what you put in comes out as something equivalent).
330 408
331For the more enlightened: note that in the following descriptions, 409For the more enlightened: note that in the following descriptions,
332lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl> 410lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>
333refers to the abstract Perl language itself. 411refers to the abstract Perl language itself.
412
334 413
335=head2 JSON -> PERL 414=head2 JSON -> PERL
336 415
337=over 4 416=over 4
338 417
359conversion details, but an integer may take slightly less memory and might 438conversion details, but an integer may take slightly less memory and might
360represent more values exactly than (floating point) numbers. 439represent more values exactly than (floating point) numbers.
361 440
362=item true, false 441=item true, false
363 442
364These JSON atoms become C<0>, C<1>, respectively. Information is lost in 443These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
365this process. Future versions might represent those values differently, 444respectively. They are overloaded to act almost exactly like the numbers
366but they will be guarenteed to act like these integers would normally in 445C<1> and C<0>. You can check wether a scalar is a JSON boolean by using
367Perl. 446the C<JSON::XS::is_bool> function.
368 447
369=item null 448=item null
370 449
371A JSON null atom becomes C<undef> in Perl. 450A JSON null atom becomes C<undef> in Perl.
372 451
373=back 452=back
453
374 454
375=head2 PERL -> JSON 455=head2 PERL -> JSON
376 456
377The mapping from Perl to JSON is slightly more difficult, as Perl is a 457The mapping from Perl to JSON is slightly more difficult, as Perl is a
378truly typeless language, so we can only guess which JSON type is meant by 458truly typeless language, so we can only guess which JSON type is meant by
381=over 4 461=over 4
382 462
383=item hash references 463=item hash references
384 464
385Perl hash references become JSON objects. As there is no inherent ordering 465Perl hash references become JSON objects. As there is no inherent ordering
386in hash keys, they will usually be encoded in a pseudo-random order that 466in hash keys (or JSON objects), they will usually be encoded in a
387can change between runs of the same program but stays generally the same 467pseudo-random order that can change between runs of the same program but
388within a single run of a program. JSON::XS can optionally sort the hash 468stays generally the same within a single run of a program. JSON::XS can
389keys (determined by the I<canonical> flag), so the same datastructure 469optionally sort the hash keys (determined by the I<canonical> flag), so
390will serialise to the same JSON text (given same settings and version of 470the same datastructure will serialise to the same JSON text (given same
391JSON::XS), but this incurs a runtime overhead. 471settings and version of JSON::XS), but this incurs a runtime overhead
472and is only rarely useful, e.g. when you want to compare some JSON text
473against another for equality.
392 474
393=item array references 475=item array references
394 476
395Perl array references become JSON arrays. 477Perl array references become JSON arrays.
478
479=item other references
480
481Other unblessed references are generally not allowed and will cause an
482exception to be thrown, except for references to the integers C<0> and
483C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
484also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
485
486 to_json [\0,JSON::XS::true] # yields [false,true]
487
488=item JSON::XS::true, JSON::XS::false
489
490These special values become JSON true and JSON false values,
491respectively. You cna alos use C<\1> and C<\0> directly if you want.
396 492
397=item blessed objects 493=item blessed objects
398 494
399Blessed objects are not allowed. JSON::XS currently tries to encode their 495Blessed objects are not allowed. JSON::XS currently tries to encode their
400underlying representation (hash- or arrayref), but this behaviour might 496underlying representation (hash- or arrayref), but this behaviour might
433 $x *= 1; # same thing, the choise is yours. 529 $x *= 1; # same thing, the choise is yours.
434 530
435You can not currently output JSON booleans or force the type in other, 531You can not currently output JSON booleans or force the type in other,
436less obscure, ways. Tell me if you need this capability. 532less obscure, ways. Tell me if you need this capability.
437 533
438=item circular data structures
439
440Those will be encoded until memory or stackspace runs out.
441
442=back 534=back
535
443 536
444=head1 COMPARISON 537=head1 COMPARISON
445 538
446As already mentioned, this module was created because none of the existing 539As already mentioned, this module was created because none of the existing
447JSON modules could be made to work correctly. First I will describe the 540JSON modules could be made to work correctly. First I will describe the
525 618
526Does not check input for validity. 619Does not check input for validity.
527 620
528=back 621=back
529 622
623
624=head2 JSON and YAML
625
626You often hear that JSON is a subset (or a close subset) of YAML. This is,
627however, a mass hysteria and very far from the truth. In general, there is
628no way to configure JSON::XS to output a data structure as valid YAML.
629
630If you really must use JSON::XS to generate YAML, you should use this
631algorithm (subject to change in future versions):
632
633 my $to_yaml = JSON::XS->new->utf8->space_after (1);
634 my $yaml = $to_yaml->encode ($ref) . "\n";
635
636This will usually generate JSON texts that also parse as valid
637YAML. Please note that YAML has hardcoded limits on (simple) object key
638lengths that JSON doesn't have, so you should make sure that your hash
639keys are noticably shorter than the 1024 characters YAML allows.
640
641There might be other incompatibilities that I am not aware of. In general
642you should not try to generate YAML with a JSON generator or vice versa,
643or try to parse JSON with a YAML parser or vice versa: chances are high
644that you will run into severe interoperability problems.
645
646
530=head2 SPEED 647=head2 SPEED
531 648
532It seems that JSON::XS is surprisingly fast, as shown in the following 649It seems that JSON::XS is surprisingly fast, as shown in the following
533tables. They have been generated with the help of the C<eg/bench> program 650tables. They have been generated with the help of the C<eg/bench> program
534in the JSON::XS distribution, to make it easy to compare on your own 651in the JSON::XS distribution, to make it easy to compare on your own
535system. 652system.
536 653
537First comes a comparison between various modules using a very short JSON 654First comes a comparison between various modules using a very short
538string: 655single-line JSON string:
539 656
540 {"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null} 657 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
658 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
541 659
542It shows the number of encodes/decodes per second (JSON::XS uses the 660It shows the number of encodes/decodes per second (JSON::XS uses
543functional interface, while JSON::XS/2 uses the OO interface with 661the functional interface, while JSON::XS/2 uses the OO interface
544pretty-printing and hashkey sorting enabled). Higher is better: 662with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
663shrink). Higher is better:
545 664
546 module | encode | decode | 665 module | encode | decode |
547 -----------|------------|------------| 666 -----------|------------|------------|
548 JSON | 11488.516 | 7823.035 | 667 JSON | 7645.468 | 4208.613 |
549 JSON::DWIW | 94708.054 | 129094.260 | 668 JSON::DWIW | 40721.398 | 77101.176 |
550 JSON::PC | 63884.157 | 128528.212 | 669 JSON::PC | 65948.176 | 78251.940 |
551 JSON::Syck | 34898.677 | 42096.911 | 670 JSON::Syck | 22844.793 | 26479.192 |
552 JSON::XS | 654027.064 | 396423.669 | 671 JSON::XS | 388361.481 | 199728.762 |
553 JSON::XS/2 | 371564.190 | 371725.613 | 672 JSON::XS/2 | 218453.333 | 192399.266 |
673 JSON::XS/3 | 338250.323 | 192399.266 |
674 Storable | 15779.925 | 14169.946 |
554 -----------+------------+------------+ 675 -----------+------------+------------+
555 676
556That is, JSON::XS is more than six times faster than JSON::DWIW on 677That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
557encoding, more than three times faster on decoding, and about thirty times 678about three times faster on decoding, and over fourty times faster
558faster than JSON, even with pretty-printing and key sorting. 679than JSON, even with pretty-printing and key sorting. It also compares
680favourably to Storable for small amounts of data.
559 681
560Using a longer test string (roughly 18KB, generated from Yahoo! Locals 682Using a longer test string (roughly 18KB, generated from Yahoo! Locals
561search API (http://nanoref.com/yahooapis/mgPdGg): 683search API (http://nanoref.com/yahooapis/mgPdGg):
562 684
563 module | encode | decode | 685 module | encode | decode |
564 -----------|------------|------------| 686 -----------|------------|------------|
565 JSON | 273.023 | 44.674 | 687 JSON | 254.685 | 37.665 |
566 JSON::DWIW | 1089.383 | 1145.704 | 688 JSON::DWIW | 843.343 | 1049.731 |
567 JSON::PC | 3097.419 | 2393.921 | 689 JSON::PC | 3602.116 | 2307.352 |
568 JSON::Syck | 514.060 | 843.053 | 690 JSON::Syck | 505.107 | 787.899 |
569 JSON::XS | 6479.668 | 3636.364 | 691 JSON::XS | 5747.196 | 3690.220 |
570 JSON::XS/2 | 3774.221 | 3599.124 | 692 JSON::XS/2 | 3968.121 | 3676.634 |
693 JSON::XS/3 | 6105.246 | 3662.508 |
694 Storable | 4417.337 | 5285.161 |
571 -----------+------------+------------+ 695 -----------+------------+------------+
572 696
573Again, JSON::XS leads by far. 697Again, JSON::XS leads by far (except for Storable which non-surprisingly
698decodes faster).
574 699
575On large strings containing lots of high unicode characters, some modules 700On large strings containing lots of high unicode characters, some modules
576(such as JSON::PC) seem to decode faster than JSON::XS, but the result 701(such as JSON::PC) seem to decode faster than JSON::XS, but the result
577will be broken due to missing (or wrong) unicode handling. Others refuse 702will be broken due to missing (or wrong) unicode handling. Others refuse
578to decode or encode properly, so it was impossible to prepare a fair 703to decode or encode properly, so it was impossible to prepare a fair
579comparison table for that case. 704comparison table for that case.
580 705
581=head1 RESOURCE LIMITS
582 706
583JSON::XS does not impose any limits on the size of JSON texts or Perl 707=head1 SECURITY CONSIDERATIONS
584values they represent - if your machine can handle it, JSON::XS will 708
585encode or decode it. Future versions might optionally impose structure 709When you are using JSON in a protocol, talking to untrusted potentially
586depth and memory use resource limits. 710hostile creatures requires relatively few measures.
711
712First of all, your JSON decoder should be secure, that is, should not have
713any buffer overflows. Obviously, this module should ensure that and I am
714trying hard on making that true, but you never know.
715
716Second, you need to avoid resource-starving attacks. That means you should
717limit the size of JSON texts you accept, or make sure then when your
718resources run out, thats just fine (e.g. by using a separate process that
719can crash safely). The size of a JSON text in octets or characters is
720usually a good indication of the size of the resources required to decode
721it into a Perl structure.
722
723Third, JSON::XS recurses using the C stack when decoding objects and
724arrays. The C stack is a limited resource: for instance, on my amd64
725machine with 8MB of stack size I can decode around 180k nested arrays but
726only 14k nested JSON objects (due to perl itself recursing deeply on croak
727to free the temporary). If that is exceeded, the program crashes. to be
728conservative, the default nesting limit is set to 512. If your process
729has a smaller stack, you should adjust this setting accordingly with the
730C<max_depth> method.
731
732And last but least, something else could bomb you that I forgot to think
733of. In that case, you get to keep the pieces. I am always open for hints,
734though...
735
736If you are using JSON::XS to return packets to consumption
737by javascript scripts in a browser you should have a look at
738L<http://jpsykes.com/47/practical-csrf-and-json-security> to see wether
739you are vulnerable to some common attack vectors (which really are browser
740design bugs, but it is still you who will have to deal with it, as major
741browser developers care only for features, not about doing security
742right).
743
587 744
588=head1 BUGS 745=head1 BUGS
589 746
590While the goal of this module is to be correct, that unfortunately does 747While the goal of this module is to be correct, that unfortunately does
591not mean its bug-free, only that I think its design is bug-free. It is 748not mean its bug-free, only that I think its design is bug-free. It is
592still very young and not well-tested. If you keep reporting bugs they will 749still relatively early in its development. If you keep reporting bugs they
593be fixed swiftly, though. 750will be fixed swiftly, though.
594 751
595=cut 752=cut
753
754our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
755our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
756
757sub true() { $true }
758sub false() { $false }
759
760sub is_bool($) {
761 UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
762 or UNIVERSAL::isa $_[0], "JSON::Literal"
763}
764
765XSLoader::load "JSON::XS", $VERSION;
766
767package JSON::XS::Boolean;
768
769use overload
770 "0+" => sub { ${$_[0]} },
771 "++" => sub { $_[0] = ${$_[0]} + 1 },
772 "--" => sub { $_[0] = ${$_[0]} - 1 },
773 fallback => 1;
596 774
5971; 7751;
598 776
599=head1 AUTHOR 777=head1 AUTHOR
600 778

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