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20 $perl_scalar = $coder->decode ($unicode_json_text); 20 $perl_scalar = $coder->decode ($unicode_json_text);
21 21
22 # Note that JSON version 2.0 and above will automatically use JSON::XS 22 # Note that JSON version 2.0 and above will automatically use JSON::XS
23 # if available, at virtually no speed overhead either, so you should 23 # if available, at virtually no speed overhead either, so you should
24 # be able to just: 24 # be able to just:
25 25
26 use JSON; 26 use JSON;
27 27
28 # and do the same things, except that you have a pure-perl fallback now. 28 # and do the same things, except that you have a pure-perl fallback now.
29 29
30DESCRIPTION 30DESCRIPTION
31 This module converts Perl data structures to JSON and vice versa. Its 31 This module converts Perl data structures to JSON and vice versa. Its
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44 to write yet another JSON module? While it seems there are many JSON 44 to write yet another JSON module? While it seems there are many JSON
45 modules, none of them correctly handle all corner cases, and in most 45 modules, none of them correctly handle all corner cases, and in most
46 cases their maintainers are unresponsive, gone missing, or not listening 46 cases their maintainers are unresponsive, gone missing, or not listening
47 to bug reports for other reasons. 47 to bug reports for other reasons.
48 48
49 See COMPARISON, below, for a comparison to some other JSON modules.
50
51 See MAPPING, below, on how JSON::XS maps perl values to JSON values and 49 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
52 vice versa. 50 vice versa.
53 51
54 FEATURES 52 FEATURES
55 * correct Unicode handling 53 * correct Unicode handling
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58 does so, and even documents what "correct" means. 56 does so, and even documents what "correct" means.
59 57
60 * round-trip integrity 58 * round-trip integrity
61 59
62 When you serialise a perl data structure using only data types 60 When you serialise a perl data structure using only data types
63 supported by JSON, the deserialised data structure is identical on 61 supported by JSON and Perl, the deserialised data structure is
64 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" 62 identical on the Perl level. (e.g. the string "2.0" doesn't suddenly
65 just because it looks like a number). There minor *are* exceptions 63 become "2" just because it looks like a number). There *are* minor
66 to this, read the MAPPING section below to learn about those. 64 exceptions to this, read the MAPPING section below to learn about
65 those.
67 66
68 * strict checking of JSON correctness 67 * strict checking of JSON correctness
69 68
70 There is no guessing, no generating of illegal JSON texts by 69 There is no guessing, no generating of illegal JSON texts by
71 default, and only JSON is accepted as input by default (the latter 70 default, and only JSON is accepted as input by default (the latter
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78 too. 77 too.
79 78
80 * simple to use 79 * simple to use
81 80
82 This module has both a simple functional interface as well as an 81 This module has both a simple functional interface as well as an
83 object oriented interface interface. 82 object oriented interface.
84 83
85 * reasonably versatile output formats 84 * reasonably versatile output formats
86 85
87 You can choose between the most compact guaranteed-single-line 86 You can choose between the most compact guaranteed-single-line
88 format possible (nice for simple line-based protocols), a pure-ASCII 87 format possible (nice for simple line-based protocols), a pure-ASCII
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113 This function call is functionally identical to: 112 This function call is functionally identical to:
114 113
115 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 114 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
116 115
117 Except being faster. 116 Except being faster.
118
119 $is_boolean = JSON::XS::is_bool $scalar
120 Returns true if the passed scalar represents either JSON::XS::true
121 or JSON::XS::false, two constants that act like 1 and 0,
122 respectively and are used to represent JSON "true" and "false"
123 values in Perl.
124
125 See MAPPING, below, for more information on how JSON values are
126 mapped to Perl.
127 117
128A FEW NOTES ON UNICODE AND PERL 118A FEW NOTES ON UNICODE AND PERL
129 Since this often leads to confusion, here are a few very clear words on 119 Since this often leads to confusion, here are a few very clear words on
130 how Unicode works in Perl, modulo bugs. 120 how Unicode works in Perl, modulo bugs.
131 121
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370 output JSON objects by sorting their keys. This is adding a 360 output JSON objects by sorting their keys. This is adding a
371 comparatively high overhead. 361 comparatively high overhead.
372 362
373 If $enable is false, then the "encode" method will output key-value 363 If $enable is false, then the "encode" method will output key-value
374 pairs in the order Perl stores them (which will likely change 364 pairs in the order Perl stores them (which will likely change
375 between runs of the same script). 365 between runs of the same script, and can change even within the same
366 run from 5.18 onwards).
376 367
377 This option is useful if you want the same data structure to be 368 This option is useful if you want the same data structure to be
378 encoded as the same JSON text (given the same overall settings). If 369 encoded as the same JSON text (given the same overall settings). If
379 it is disabled, the same hash might be encoded differently even if 370 it is disabled, the same hash might be encoded differently even if
380 contains the same data, as key-value pairs have no inherent ordering 371 contains the same data, as key-value pairs have no inherent ordering
381 in Perl. 372 in Perl.
382 373
383 This setting has no effect when decoding JSON texts. 374 This setting has no effect when decoding JSON texts.
375
376 This setting has currently no effect on tied hashes.
384 377
385 $json = $json->allow_nonref ([$enable]) 378 $json = $json->allow_nonref ([$enable])
386 $enabled = $json->get_allow_nonref 379 $enabled = $json->get_allow_nonref
387 If $enable is true (or missing), then the "encode" method can 380 If $enable is true (or missing), then the "encode" method can
388 convert a non-reference into its corresponding string, number or 381 convert a non-reference into its corresponding string, number or
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415 recommended to leave it off unless you know your communications 408 recommended to leave it off unless you know your communications
416 partner. 409 partner.
417 410
418 $json = $json->allow_blessed ([$enable]) 411 $json = $json->allow_blessed ([$enable])
419 $enabled = $json->get_allow_blessed 412 $enabled = $json->get_allow_blessed
413 See "OBJECT SERIALISATION" for details.
414
420 If $enable is true (or missing), then the "encode" method will not 415 If $enable is true (or missing), then the "encode" method will not
421 barf when it encounters a blessed reference. Instead, the value of 416 barf when it encounters a blessed reference that it cannot convert
422 the convert_blessed option will decide whether "null" 417 otherwise. Instead, a JSON "null" value is encoded instead of the
423 ("convert_blessed" disabled or no "TO_JSON" method found) or a 418 object.
424 representation of the object ("convert_blessed" enabled and
425 "TO_JSON" method found) is being encoded. Has no effect on "decode".
426 419
427 If $enable is false (the default), then "encode" will throw an 420 If $enable is false (the default), then "encode" will throw an
428 exception when it encounters a blessed object. 421 exception when it encounters a blessed object that it cannot convert
422 otherwise.
423
424 This setting has no effect on "decode".
429 425
430 $json = $json->convert_blessed ([$enable]) 426 $json = $json->convert_blessed ([$enable])
431 $enabled = $json->get_convert_blessed 427 $enabled = $json->get_convert_blessed
428 See "OBJECT SERIALISATION" for details.
429
432 If $enable is true (or missing), then "encode", upon encountering a 430 If $enable is true (or missing), then "encode", upon encountering a
433 blessed object, will check for the availability of the "TO_JSON" 431 blessed object, will check for the availability of the "TO_JSON"
434 method on the object's class. If found, it will be called in scalar 432 method on the object's class. If found, it will be called in scalar
435 context and the resulting scalar will be encoded instead of the 433 context and the resulting scalar will be encoded instead of the
436 object. If no "TO_JSON" method is found, the value of 434 object.
437 "allow_blessed" will decide what to do.
438 435
439 The "TO_JSON" method may safely call die if it wants. If "TO_JSON" 436 The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
440 returns other blessed objects, those will be handled in the same 437 returns other blessed objects, those will be handled in the same
441 way. "TO_JSON" must take care of not causing an endless recursion 438 way. "TO_JSON" must take care of not causing an endless recursion
442 cycle (== crash) in this case. The name of "TO_JSON" was chosen 439 cycle (== crash) in this case. The name of "TO_JSON" was chosen
443 because other methods called by the Perl core (== not by the user of 440 because other methods called by the Perl core (== not by the user of
444 the object) are usually in upper case letters and to avoid 441 the object) are usually in upper case letters and to avoid
445 collisions with any "to_json" function or method. 442 collisions with any "to_json" function or method.
446 443
447 This setting does not yet influence "decode" in any way, but in the 444 If $enable is false (the default), then "encode" will not consider
448 future, global hooks might get installed that influence "decode" and 445 this type of conversion.
449 are enabled by this setting.
450 446
451 If $enable is false, then the "allow_blessed" setting will decide 447 This setting has no effect on "decode".
452 what to do when a blessed object is found. 448
449 $json = $json->allow_tags ([$enable])
450 $enabled = $json->allow_tags
451 See "OBJECT SERIALISATION" for details.
452
453 If $enable is true (or missing), then "encode", upon encountering a
454 blessed object, will check for the availability of the "FREEZE"
455 method on the object's class. If found, it will be used to serialise
456 the object into a nonstandard tagged JSON value (that JSON decoders
457 cannot decode).
458
459 It also causes "decode" to parse such tagged JSON values and
460 deserialise them via a call to the "THAW" method.
461
462 If $enable is false (the default), then "encode" will not consider
463 this type of conversion, and tagged JSON values will cause a parse
464 error in "decode", as if tags were not part of the grammar.
453 465
454 $json = $json->filter_json_object ([$coderef->($hashref)]) 466 $json = $json->filter_json_object ([$coderef->($hashref)])
455 When $coderef is specified, it will be called from "decode" each 467 When $coderef is specified, it will be called from "decode" each
456 time it decodes a JSON object. The only argument is a reference to 468 time it decodes a JSON object. The only argument is a reference to
457 the newly-created hash. If the code references returns a single 469 the newly-created hash. If the code references returns a single
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593 605
594 See SECURITY CONSIDERATIONS, below, for more info on why this is 606 See SECURITY CONSIDERATIONS, below, for more info on why this is
595 useful. 607 useful.
596 608
597 $json_text = $json->encode ($perl_scalar) 609 $json_text = $json->encode ($perl_scalar)
598 Converts the given Perl data structure (a simple scalar or a 610 Converts the given Perl value or data structure to its JSON
599 reference to a hash or array) to its JSON representation. Simple 611 representation. Croaks on error.
600 scalars will be converted into JSON string or number sequences,
601 while references to arrays become JSON arrays and references to
602 hashes become JSON objects. Undefined Perl values (e.g. "undef")
603 become JSON "null" values. Neither "true" nor "false" values will be
604 generated.
605 612
606 $perl_scalar = $json->decode ($json_text) 613 $perl_scalar = $json->decode ($json_text)
607 The opposite of "encode": expects a JSON text and tries to parse it, 614 The opposite of "encode": expects a JSON text and tries to parse it,
608 returning the resulting simple scalar or reference. Croaks on error. 615 returning the resulting simple scalar or reference. Croaks on error.
609
610 JSON numbers and strings become simple Perl scalars. JSON arrays
611 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
612 becomes 1, "false" becomes 0 and "null" becomes "undef".
613 616
614 ($perl_scalar, $characters) = $json->decode_prefix ($json_text) 617 ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
615 This works like the "decode" method, but instead of raising an 618 This works like the "decode" method, but instead of raising an
616 exception when there is trailing garbage after the first JSON 619 exception when there is trailing garbage after the first JSON
617 object, it will silently stop parsing there and return the number of 620 object, it will silently stop parsing there and return the number of
618 characters consumed so far. 621 characters consumed so far.
619 622
620 This is useful if your JSON texts are not delimited by an outer 623 This is useful if your JSON texts are not delimited by an outer
621 protocol (which is not the brightest thing to do in the first place)
622 and you need to know where the JSON text ends. 624 protocol and you need to know where the JSON text ends.
623 625
624 JSON::XS->new->decode_prefix ("[1] the tail") 626 JSON::XS->new->decode_prefix ("[1] the tail")
625 => ([], 3) 627 => ([], 3)
626 628
627INCREMENTAL PARSING 629INCREMENTAL PARSING
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635 calls). 637 calls).
636 638
637 JSON::XS will only attempt to parse the JSON text once it is sure it has 639 JSON::XS will only attempt to parse the JSON text once it is sure it has
638 enough text to get a decisive result, using a very simple but truly 640 enough text to get a decisive result, using a very simple but truly
639 incremental parser. This means that it sometimes won't stop as early as 641 incremental parser. This means that it sometimes won't stop as early as
640 the full parser, for example, it doesn't detect parenthese mismatches. 642 the full parser, for example, it doesn't detect mismatched parentheses.
641 The only thing it guarantees is that it starts decoding as soon as a 643 The only thing it guarantees is that it starts decoding as soon as a
642 syntactically valid JSON text has been seen. This means you need to set 644 syntactically valid JSON text has been seen. This means you need to set
643 resource limits (e.g. "max_size") to ensure the parser will stop parsing 645 resource limits (e.g. "max_size") to ensure the parser will stop parsing
644 in the presence if syntax errors. 646 in the presence if syntax errors.
645 647
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659 661
660 If the method is called in scalar context, then it will try to 662 If the method is called in scalar context, then it will try to
661 extract exactly *one* JSON object. If that is successful, it will 663 extract exactly *one* JSON object. If that is successful, it will
662 return this object, otherwise it will return "undef". If there is a 664 return this object, otherwise it will return "undef". If there is a
663 parse error, this method will croak just as "decode" would do (one 665 parse error, this method will croak just as "decode" would do (one
664 can then use "incr_skip" to skip the errornous part). This is the 666 can then use "incr_skip" to skip the erroneous part). This is the
665 most common way of using the method. 667 most common way of using the method.
666 668
667 And finally, in list context, it will try to extract as many objects 669 And finally, in list context, it will try to extract as many objects
668 from the stream as it can find and return them, or the empty list 670 from the stream as it can find and return them, or the empty list
669 otherwise. For this to work, there must be no separators between the 671 otherwise. For this to work, there must be no separators between the
670 JSON objects or arrays, instead they must be concatenated 672 JSON objects or arrays, instead they must be concatenated
671 back-to-back. If an error occurs, an exception will be raised as in 673 back-to-back. If an error occurs, an exception will be raised as in
672 the scalar context case. Note that in this case, any 674 the scalar context case. Note that in this case, any
673 previously-parsed JSON texts will be lost. 675 previously-parsed JSON texts will be lost.
676
677 Example: Parse some JSON arrays/objects in a given string and return
678 them.
679
680 my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
674 681
675 $lvalue_string = $json->incr_text 682 $lvalue_string = $json->incr_text
676 This method returns the currently stored JSON fragment as an lvalue, 683 This method returns the currently stored JSON fragment as an lvalue,
677 that is, you can manipulate it. This *only* works when a preceding 684 that is, you can manipulate it. This *only* works when a preceding
678 call to "incr_parse" in *scalar context* successfully returned an 685 call to "incr_parse" in *scalar context* successfully returned an
… …
686 after a JSON object or b) parsing multiple JSON objects separated by 693 after a JSON object or b) parsing multiple JSON objects separated by
687 non-JSON text (such as commas). 694 non-JSON text (such as commas).
688 695
689 $json->incr_skip 696 $json->incr_skip
690 This will reset the state of the incremental parser and will remove 697 This will reset the state of the incremental parser and will remove
691 the parsed text from the input buffer. This is useful after 698 the parsed text from the input buffer so far. This is useful after
692 "incr_parse" died, in which case the input buffer and incremental 699 "incr_parse" died, in which case the input buffer and incremental
693 parser state is left unchanged, to skip the text parsed so far and 700 parser state is left unchanged, to skip the text parsed so far and
694 to reset the parse state. 701 to reset the parse state.
695 702
703 The difference to "incr_reset" is that only text until the parse
704 error occurred is removed.
705
696 $json->incr_reset 706 $json->incr_reset
697 This completely resets the incremental parser, that is, after this 707 This completely resets the incremental parser, that is, after this
698 call, it will be as if the parser had never parsed anything. 708 call, it will be as if the parser had never parsed anything.
699 709
700 This is useful if you want ot repeatedly parse JSON objects and want 710 This is useful if you want to repeatedly parse JSON objects and want
701 to ignore any trailing data, which means you have to reset the 711 to ignore any trailing data, which means you have to reset the
702 parser after each successful decode. 712 parser after each successful decode.
703 713
704 LIMITATIONS 714 LIMITATIONS
705 All options that affect decoding are supported, except "allow_nonref". 715 All options that affect decoding are supported, except "allow_nonref".
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883 If the number consists of digits only, JSON::XS will try to 893 If the number consists of digits only, JSON::XS will try to
884 represent it as an integer value. If that fails, it will try to 894 represent it as an integer value. If that fails, it will try to
885 represent it as a numeric (floating point) value if that is possible 895 represent it as a numeric (floating point) value if that is possible
886 without loss of precision. Otherwise it will preserve the number as 896 without loss of precision. Otherwise it will preserve the number as
887 a string value (in which case you lose roundtripping ability, as the 897 a string value (in which case you lose roundtripping ability, as the
888 JSON number will be re-encoded toa JSON string). 898 JSON number will be re-encoded to a JSON string).
889 899
890 Numbers containing a fractional or exponential part will always be 900 Numbers containing a fractional or exponential part will always be
891 represented as numeric (floating point) values, possibly at a loss 901 represented as numeric (floating point) values, possibly at a loss
892 of precision (in which case you might lose perfect roundtripping 902 of precision (in which case you might lose perfect roundtripping
893 ability, but the JSON number will still be re-encoded as a JSON 903 ability, but the JSON number will still be re-encoded as a JSON
894 number). 904 number).
895 905
906 Note that precision is not accuracy - binary floating point values
907 cannot represent most decimal fractions exactly, and when converting
908 from and to floating point, JSON::XS only guarantees precision up to
909 but not including the least significant bit.
910
896 true, false 911 true, false
897 These JSON atoms become "JSON::XS::true" and "JSON::XS::false", 912 These JSON atoms become "Types::Serialiser::true" and
898 respectively. They are overloaded to act almost exactly like the 913 "Types::Serialiser::false", respectively. They are overloaded to act
899 numbers 1 and 0. You can check whether a scalar is a JSON boolean by 914 almost exactly like the numbers 1 and 0. You can check whether a
900 using the "JSON::XS::is_bool" function. 915 scalar is a JSON boolean by using the "Types::Serialiser::is_bool"
916 function (after "use Types::Serialier", of course).
901 917
902 null 918 null
903 A JSON null atom becomes "undef" in Perl. 919 A JSON null atom becomes "undef" in Perl.
920
921 shell-style comments ("# *text*")
922 As a nonstandard extension to the JSON syntax that is enabled by the
923 "relaxed" setting, shell-style comments are allowed. They can start
924 anywhere outside strings and go till the end of the line.
925
926 tagged values ("(*tag*)*value*").
927 Another nonstandard extension to the JSON syntax, enabled with the
928 "allow_tags" setting, are tagged values. In this implementation, the
929 *tag* must be a perl package/class name encoded as a JSON string,
930 and the *value* must be a JSON array encoding optional constructor
931 arguments.
932
933 See "OBJECT SERIALISATION", below, for details.
904 934
905 PERL -> JSON 935 PERL -> JSON
906 The mapping from Perl to JSON is slightly more difficult, as Perl is a 936 The mapping from Perl to JSON is slightly more difficult, as Perl is a
907 truly typeless language, so we can only guess which JSON type is meant 937 truly typeless language, so we can only guess which JSON type is meant
908 by a Perl value. 938 by a Perl value.
909 939
910 hash references 940 hash references
911 Perl hash references become JSON objects. As there is no inherent 941 Perl hash references become JSON objects. As there is no inherent
912 ordering in hash keys (or JSON objects), they will usually be 942 ordering in hash keys (or JSON objects), they will usually be
913 encoded in a pseudo-random order that can change between runs of the 943 encoded in a pseudo-random order. JSON::XS can optionally sort the
914 same program but stays generally the same within a single run of a 944 hash keys (determined by the *canonical* flag), so the same
915 program. JSON::XS can optionally sort the hash keys (determined by 945 datastructure will serialise to the same JSON text (given same
916 the *canonical* flag), so the same datastructure will serialise to 946 settings and version of JSON::XS), but this incurs a runtime
917 the same JSON text (given same settings and version of JSON::XS), 947 overhead and is only rarely useful, e.g. when you want to compare
918 but this incurs a runtime overhead and is only rarely useful, e.g. 948 some JSON text against another for equality.
919 when you want to compare some JSON text against another for
920 equality.
921 949
922 array references 950 array references
923 Perl array references become JSON arrays. 951 Perl array references become JSON arrays.
924 952
925 other references 953 other references
926 Other unblessed references are generally not allowed and will cause 954 Other unblessed references are generally not allowed and will cause
927 an exception to be thrown, except for references to the integers 0 955 an exception to be thrown, except for references to the integers 0
928 and 1, which get turned into "false" and "true" atoms in JSON. You 956 and 1, which get turned into "false" and "true" atoms in JSON.
929 can also use "JSON::XS::false" and "JSON::XS::true" to improve 957
958 Since "JSON::XS" uses the boolean model from Types::Serialiser, you
959 can also "use Types::Serialiser" and then use
960 "Types::Serialiser::false" and "Types::Serialiser::true" to improve
930 readability. 961 readability.
931 962
963 use Types::Serialiser;
932 encode_json [\0, JSON::XS::true] # yields [false,true] 964 encode_json [\0, Types::Serialiser::true] # yields [false,true]
933 965
934 JSON::XS::true, JSON::XS::false 966 Types::Serialiser::true, Types::Serialiser::false
935 These special values become JSON true and JSON false values, 967 These special values from the Types::Serialiser module become JSON
936 respectively. You can also use "\1" and "\0" directly if you want. 968 true and JSON false values, respectively. You can also use "\1" and
969 "\0" directly if you want.
937 970
938 blessed objects 971 blessed objects
939 Blessed objects are not directly representable in JSON. See the 972 Blessed objects are not directly representable in JSON, but
940 "allow_blessed" and "convert_blessed" methods on various options on 973 "JSON::XS" allows various ways of handling objects. See "OBJECT
941 how to deal with this: basically, you can choose between throwing an 974 SERIALISATION", below, for details.
942 exception, encoding the reference as if it weren't blessed, or
943 provide your own serialiser method.
944 975
945 simple scalars 976 simple scalars
946 Simple Perl scalars (any scalar that is not a reference) are the 977 Simple Perl scalars (any scalar that is not a reference) are the
947 most difficult objects to encode: JSON::XS will encode undefined 978 most difficult objects to encode: JSON::XS will encode undefined
948 scalars as JSON "null" values, scalars that have last been used in a 979 scalars as JSON "null" values, scalars that have last been used in a
… …
976 1007
977 You can not currently force the type in other, less obscure, ways. 1008 You can not currently force the type in other, less obscure, ways.
978 Tell me if you need this capability (but don't forget to explain why 1009 Tell me if you need this capability (but don't forget to explain why
979 it's needed :). 1010 it's needed :).
980 1011
1012 Note that numerical precision has the same meaning as under Perl (so
1013 binary to decimal conversion follows the same rules as in Perl,
1014 which can differ to other languages). Also, your perl interpreter
1015 might expose extensions to the floating point numbers of your
1016 platform, such as infinities or NaN's - these cannot be represented
1017 in JSON, and it is an error to pass those in.
1018
1019 OBJECT SERIALISATION
1020 As JSON cannot directly represent Perl objects, you have to choose
1021 between a pure JSON representation (without the ability to deserialise
1022 the object automatically again), and a nonstandard extension to the JSON
1023 syntax, tagged values.
1024
1025 SERIALISATION
1026 What happens when "JSON::XS" encounters a Perl object depends on the
1027 "allow_blessed", "convert_blessed" and "allow_tags" settings, which are
1028 used in this order:
1029
1030 1. "allow_tags" is enabled and the object has a "FREEZE" method.
1031 In this case, "JSON::XS" uses the Types::Serialiser object
1032 serialisation protocol to create a tagged JSON value, using a
1033 nonstandard extension to the JSON syntax.
1034
1035 This works by invoking the "FREEZE" method on the object, with the
1036 first argument being the object to serialise, and the second
1037 argument being the constant string "JSON" to distinguish it from
1038 other serialisers.
1039
1040 The "FREEZE" method can return any number of values (i.e. zero or
1041 more). These values and the paclkage/classname of the object will
1042 then be encoded as a tagged JSON value in the following format:
1043
1044 ("classname")[FREEZE return values...]
1045
1046 For example, the hypothetical "My::Object" "FREEZE" method might use
1047 the objects "type" and "id" members to encode the object:
1048
1049 sub My::Object::FREEZE {
1050 my ($self, $serialiser) = @_;
1051
1052 ($self->{type}, $self->{id})
1053 }
1054
1055 2. "convert_blessed" is enabled and the object has a "TO_JSON" method.
1056 In this case, the "TO_JSON" method of the object is invoked in
1057 scalar context. It must return a single scalar that can be directly
1058 encoded into JSON. This scalar replaces the object in the JSON text.
1059
1060 For example, the following "TO_JSON" method will convert all URI
1061 objects to JSON strings when serialised. The fatc that these values
1062 originally were URI objects is lost.
1063
1064 sub URI::TO_JSON {
1065 my ($uri) = @_;
1066 $uri->as_string
1067 }
1068
1069 3. "allow_blessed" is enabled.
1070 The object will be serialised as a JSON null value.
1071
1072 4. none of the above
1073 If none of the settings are enabled or the respective methods are
1074 missing, "JSON::XS" throws an exception.
1075
1076 DESERIALISATION
1077 For deserialisation there are only two cases to consider: either
1078 nonstandard tagging was used, in which case "allow_tags" decides, or
1079 objects cannot be automatically be deserialised, in which case you can
1080 use postprocessing or the "filter_json_object" or
1081 "filter_json_single_key_object" callbacks to get some real objects our
1082 of your JSON.
1083
1084 This section only considers the tagged value case: I a tagged JSON
1085 object is encountered during decoding and "allow_tags" is disabled, a
1086 parse error will result (as if tagged values were not part of the
1087 grammar).
1088
1089 If "allow_tags" is enabled, "JSON::XS" will look up the "THAW" method of
1090 the package/classname used during serialisation (it will not attempt to
1091 load the package as a Perl module). If there is no such method, the
1092 decoding will fail with an error.
1093
1094 Otherwise, the "THAW" method is invoked with the classname as first
1095 argument, the constant string "JSON" as second argument, and all the
1096 values from the JSON array (the values originally returned by the
1097 "FREEZE" method) as remaining arguments.
1098
1099 The method must then return the object. While technically you can return
1100 any Perl scalar, you might have to enable the "enable_nonref" setting to
1101 make that work in all cases, so better return an actual blessed
1102 reference.
1103
1104 As an example, let's implement a "THAW" function that regenerates the
1105 "My::Object" from the "FREEZE" example earlier:
1106
1107 sub My::Object::THAW {
1108 my ($class, $serialiser, $type, $id) = @_;
1109
1110 $class->new (type => $type, id => $id)
1111 }
1112
981ENCODING/CODESET FLAG NOTES 1113ENCODING/CODESET FLAG NOTES
982 The interested reader might have seen a number of flags that signify 1114 The interested reader might have seen a number of flags that signify
983 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be 1115 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
984 some confusion on what these do, so here is a short comparison: 1116 some confusion on what these do, so here is a short comparison:
985 1117
… …
1004 1136
1005 "utf8" flag disabled 1137 "utf8" flag disabled
1006 When "utf8" is disabled (the default), then "encode"/"decode" 1138 When "utf8" is disabled (the default), then "encode"/"decode"
1007 generate and expect Unicode strings, that is, characters with high 1139 generate and expect Unicode strings, that is, characters with high
1008 ordinal Unicode values (> 255) will be encoded as such characters, 1140 ordinal Unicode values (> 255) will be encoded as such characters,
1009 and likewise such characters are decoded as-is, no canges to them 1141 and likewise such characters are decoded as-is, no changes to them
1010 will be done, except "(re-)interpreting" them as Unicode codepoints 1142 will be done, except "(re-)interpreting" them as Unicode codepoints
1011 or Unicode characters, respectively (to Perl, these are the same 1143 or Unicode characters, respectively (to Perl, these are the same
1012 thing in strings unless you do funny/weird/dumb stuff). 1144 thing in strings unless you do funny/weird/dumb stuff).
1013 1145
1014 This is useful when you want to do the encoding yourself (e.g. when 1146 This is useful when you want to do the encoding yourself (e.g. when
… …
1071 structure back. This is useful when your channel for JSON transfer 1203 structure back. This is useful when your channel for JSON transfer
1072 is not 8-bit clean or the encoding might be mangled in between (e.g. 1204 is not 8-bit clean or the encoding might be mangled in between (e.g.
1073 in mail), and works because ASCII is a proper subset of most 8-bit 1205 in mail), and works because ASCII is a proper subset of most 8-bit
1074 and multibyte encodings in use in the world. 1206 and multibyte encodings in use in the world.
1075 1207
1208 JSON and ECMAscript
1209 JSON syntax is based on how literals are represented in javascript (the
1210 not-standardised predecessor of ECMAscript) which is presumably why it
1211 is called "JavaScript Object Notation".
1212
1213 However, JSON is not a subset (and also not a superset of course) of
1214 ECMAscript (the standard) or javascript (whatever browsers actually
1215 implement).
1216
1217 If you want to use javascript's "eval" function to "parse" JSON, you
1218 might run into parse errors for valid JSON texts, or the resulting data
1219 structure might not be queryable:
1220
1221 One of the problems is that U+2028 and U+2029 are valid characters
1222 inside JSON strings, but are not allowed in ECMAscript string literals,
1223 so the following Perl fragment will not output something that can be
1224 guaranteed to be parsable by javascript's "eval":
1225
1226 use JSON::XS;
1227
1228 print encode_json [chr 0x2028];
1229
1230 The right fix for this is to use a proper JSON parser in your javascript
1231 programs, and not rely on "eval" (see for example Douglas Crockford's
1232 json2.js parser).
1233
1234 If this is not an option, you can, as a stop-gap measure, simply encode
1235 to ASCII-only JSON:
1236
1237 use JSON::XS;
1238
1239 print JSON::XS->new->ascii->encode ([chr 0x2028]);
1240
1241 Note that this will enlarge the resulting JSON text quite a bit if you
1242 have many non-ASCII characters. You might be tempted to run some regexes
1243 to only escape U+2028 and U+2029, e.g.:
1244
1245 # DO NOT USE THIS!
1246 my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
1247 $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
1248 $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
1249 print $json;
1250
1251 Note that *this is a bad idea*: the above only works for U+2028 and
1252 U+2029 and thus only for fully ECMAscript-compliant parsers. Many
1253 existing javascript implementations, however, have issues with other
1254 characters as well - using "eval" naively simply *will* cause problems.
1255
1256 Another problem is that some javascript implementations reserve some
1257 property names for their own purposes (which probably makes them
1258 non-ECMAscript-compliant). For example, Iceweasel reserves the
1259 "__proto__" property name for its own purposes.
1260
1261 If that is a problem, you could parse try to filter the resulting JSON
1262 output for these property strings, e.g.:
1263
1264 $json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
1265
1266 This works because "__proto__" is not valid outside of strings, so every
1267 occurrence of ""__proto__"\s*:" must be a string used as property name.
1268
1269 If you know of other incompatibilities, please let me know.
1270
1076 JSON and YAML 1271 JSON and YAML
1077 You often hear that JSON is a subset of YAML. This is, however, a mass 1272 You often hear that JSON is a subset of YAML. This is, however, a mass
1078 hysteria(*) and very far from the truth (as of the time of this 1273 hysteria(*) and very far from the truth (as of the time of this
1079 writing), so let me state it clearly: *in general, there is no way to 1274 writing), so let me state it clearly: *in general, there is no way to
1080 configure JSON::XS to output a data structure as valid YAML* that works 1275 configure JSON::XS to output a data structure as valid YAML* that works
… …
1087 my $yaml = $to_yaml->encode ($ref) . "\n"; 1282 my $yaml = $to_yaml->encode ($ref) . "\n";
1088 1283
1089 This will *usually* generate JSON texts that also parse as valid YAML. 1284 This will *usually* generate JSON texts that also parse as valid YAML.
1090 Please note that YAML has hardcoded limits on (simple) object key 1285 Please note that YAML has hardcoded limits on (simple) object key
1091 lengths that JSON doesn't have and also has different and incompatible 1286 lengths that JSON doesn't have and also has different and incompatible
1092 unicode handling, so you should make sure that your hash keys are 1287 unicode character escape syntax, so you should make sure that your hash
1093 noticeably shorter than the 1024 "stream characters" YAML allows and 1288 keys are noticeably shorter than the 1024 "stream characters" YAML
1094 that you do not have characters with codepoint values outside the 1289 allows and that you do not have characters with codepoint values outside
1095 Unicode BMP (basic multilingual page). YAML also does not allow "\/" 1290 the Unicode BMP (basic multilingual page). YAML also does not allow "\/"
1096 sequences in strings (which JSON::XS does not *currently* generate, but 1291 sequences in strings (which JSON::XS does not *currently* generate, but
1097 other JSON generators might). 1292 other JSON generators might).
1098 1293
1099 There might be other incompatibilities that I am not aware of (or the 1294 There might be other incompatibilities that I am not aware of (or the
1100 YAML specification has been changed yet again - it does so quite often). 1295 YAML specification has been changed yet again - it does so quite often).
… …
1117 (which is not that difficult or long) and finally make YAML 1312 (which is not that difficult or long) and finally make YAML
1118 compatible to it, and educating users about the changes, instead of 1313 compatible to it, and educating users about the changes, instead of
1119 spreading lies about the real compatibility for many *years* and 1314 spreading lies about the real compatibility for many *years* and
1120 trying to silence people who point out that it isn't true. 1315 trying to silence people who point out that it isn't true.
1121 1316
1317 Addendum/2009: the YAML 1.2 spec is still incompatible with JSON,
1318 even though the incompatibilities have been documented (and are
1319 known to Brian) for many years and the spec makes explicit claims
1320 that YAML is a superset of JSON. It would be so easy to fix, but
1321 apparently, bullying people and corrupting userdata is so much
1322 easier.
1323
1122 SPEED 1324 SPEED
1123 It seems that JSON::XS is surprisingly fast, as shown in the following 1325 It seems that JSON::XS is surprisingly fast, as shown in the following
1124 tables. They have been generated with the help of the "eg/bench" program 1326 tables. They have been generated with the help of the "eg/bench" program
1125 in the JSON::XS distribution, to make it easy to compare on your own 1327 in the JSON::XS distribution, to make it easy to compare on your own
1126 system. 1328 system.
… …
1129 single-line JSON string (also available at 1331 single-line JSON string (also available at
1130 <http://dist.schmorp.de/misc/json/short.json>). 1332 <http://dist.schmorp.de/misc/json/short.json>).
1131 1333
1132 {"method": "handleMessage", "params": ["user1", 1334 {"method": "handleMessage", "params": ["user1",
1133 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7, 1335 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1134 true, false]} 1336 1, 0]}
1135 1337
1136 It shows the number of encodes/decodes per second (JSON::XS uses the 1338 It shows the number of encodes/decodes per second (JSON::XS uses the
1137 functional interface, while JSON::XS/2 uses the OO interface with 1339 functional interface, while JSON::XS/2 uses the OO interface with
1138 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). 1340 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink.
1139 Higher is better: 1341 JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses
1342 the from_json method). Higher is better:
1140 1343
1141 module | encode | decode | 1344 module | encode | decode |
1142 -----------|------------|------------| 1345 --------------|------------|------------|
1143 JSON 1.x | 4990.842 | 4088.813 | 1346 JSON::DWIW/DS | 86302.551 | 102300.098 |
1144 JSON::DWIW | 51653.990 | 71575.154 | 1347 JSON::DWIW/FJ | 86302.551 | 75983.768 |
1145 JSON::PC | 65948.176 | 74631.744 | 1348 JSON::PP | 15827.562 | 6638.658 |
1146 JSON::PP | 8931.652 | 3817.168 | 1349 JSON::Syck | 63358.066 | 47662.545 |
1147 JSON::Syck | 24877.248 | 27776.848 | 1350 JSON::XS | 511500.488 | 511500.488 |
1148 JSON::XS | 388361.481 | 227951.304 | 1351 JSON::XS/2 | 291271.111 | 388361.481 |
1149 JSON::XS/2 | 227951.304 | 218453.333 | 1352 JSON::XS/3 | 361577.931 | 361577.931 |
1150 JSON::XS/3 | 338250.323 | 218453.333 | 1353 Storable | 66788.280 | 265462.278 |
1151 Storable | 16500.016 | 135300.129 |
1152 -----------+------------+------------+ 1354 --------------+------------+------------+
1153 1355
1154 That is, JSON::XS is about five times faster than JSON::DWIW on 1356 That is, JSON::XS is almost six times faster than JSON::DWIW on
1155 encoding, about three times faster on decoding, and over forty times 1357 encoding, about five times faster on decoding, and over thirty to
1156 faster than JSON, even with pretty-printing and key sorting. It also 1358 seventy times faster than JSON's pure perl implementation. It also
1157 compares favourably to Storable for small amounts of data. 1359 compares favourably to Storable for small amounts of data.
1158 1360
1159 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1361 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
1160 search API (<http://dist.schmorp.de/misc/json/long.json>). 1362 search API (<http://dist.schmorp.de/misc/json/long.json>).
1161 1363
1162 module | encode | decode | 1364 module | encode | decode |
1163 -----------|------------|------------| 1365 --------------|------------|------------|
1164 JSON 1.x | 55.260 | 34.971 | 1366 JSON::DWIW/DS | 1647.927 | 2673.916 |
1165 JSON::DWIW | 825.228 | 1082.513 | 1367 JSON::DWIW/FJ | 1630.249 | 2596.128 |
1166 JSON::PC | 3571.444 | 2394.829 |
1167 JSON::PP | 210.987 | 32.574 | 1368 JSON::PP | 400.640 | 62.311 |
1168 JSON::Syck | 552.551 | 787.544 | 1369 JSON::Syck | 1481.040 | 1524.869 |
1169 JSON::XS | 5780.463 | 4854.519 | 1370 JSON::XS | 20661.596 | 9541.183 |
1170 JSON::XS/2 | 3869.998 | 4798.975 | 1371 JSON::XS/2 | 10683.403 | 9416.938 |
1171 JSON::XS/3 | 5862.880 | 4798.975 | 1372 JSON::XS/3 | 20661.596 | 9400.054 |
1172 Storable | 4445.002 | 5235.027 | 1373 Storable | 19765.806 | 10000.725 |
1173 -----------+------------+------------+ 1374 --------------+------------+------------+
1174 1375
1175 Again, JSON::XS leads by far (except for Storable which non-surprisingly 1376 Again, JSON::XS leads by far (except for Storable which non-surprisingly
1176 decodes faster). 1377 decodes a bit faster).
1177 1378
1178 On large strings containing lots of high Unicode characters, some 1379 On large strings containing lots of high Unicode characters, some
1179 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the 1380 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
1180 result will be broken due to missing (or wrong) Unicode handling. Others 1381 result will be broken due to missing (or wrong) Unicode handling. Others
1181 refuse to decode or encode properly, so it was impossible to prepare a 1382 refuse to decode or encode properly, so it was impossible to prepare a
… …
1216 information you might want to make sure that exceptions thrown by 1417 information you might want to make sure that exceptions thrown by
1217 JSON::XS will not end up in front of untrusted eyes. 1418 JSON::XS will not end up in front of untrusted eyes.
1218 1419
1219 If you are using JSON::XS to return packets to consumption by JavaScript 1420 If you are using JSON::XS to return packets to consumption by JavaScript
1220 scripts in a browser you should have a look at 1421 scripts in a browser you should have a look at
1221 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether 1422 <http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/>
1222 you are vulnerable to some common attack vectors (which really are 1423 to see whether you are vulnerable to some common attack vectors (which
1223 browser design bugs, but it is still you who will have to deal with it, 1424 really are browser design bugs, but it is still you who will have to
1224 as major browser developers care only for features, not about getting 1425 deal with it, as major browser developers care only for features, not
1225 security right). 1426 about getting security right).
1427
1428INTEROPERABILITY WITH OTHER MODULES
1429 "JSON::XS" uses the Types::Serialiser module to provide boolean
1430 constants. That means that the JSON true and false values will be
1431 comaptible to true and false values of iother modules that do the same,
1432 such as JSON::PP and CBOR::XS.
1226 1433
1227THREADS 1434THREADS
1228 This module is *not* guaranteed to be thread safe and there are no plans 1435 This module is *not* guaranteed to be thread safe and there are no plans
1229 to change this until Perl gets thread support (as opposed to the 1436 to change this until Perl gets thread support (as opposed to the
1230 horribly slow so-called "threads" which are simply slow and bloated 1437 horribly slow so-called "threads" which are simply slow and bloated
1231 process simulations - use fork, it's *much* faster, cheaper, better). 1438 process simulations - use fork, it's *much* faster, cheaper, better).
1232 1439
1233 (It might actually work, but you have been warned). 1440 (It might actually work, but you have been warned).
1234 1441
1442THE PERILS OF SETLOCALE
1443 Sometimes people avoid the Perl locale support and directly call the
1444 system's setlocale function with "LC_ALL".
1445
1446 This breaks both perl and modules such as JSON::XS, as stringification
1447 of numbers no longer works correctly (e.g. "$x = 0.1; print "$x"+1"
1448 might print 1, and JSON::XS might output illegal JSON as JSON::XS relies
1449 on perl to stringify numbers).
1450
1451 The solution is simple: don't call "setlocale", or use it for only those
1452 categories you need, such as "LC_MESSAGES" or "LC_CTYPE".
1453
1454 If you need "LC_NUMERIC", you should enable it only around the code that
1455 actually needs it (avoiding stringification of numbers), and restore it
1456 afterwards.
1457
1235BUGS 1458BUGS
1236 While the goal of this module is to be correct, that unfortunately does 1459 While the goal of this module is to be correct, that unfortunately does
1237 not mean it's bug-free, only that I think its design is bug-free. If you 1460 not mean it's bug-free, only that I think its design is bug-free. If you
1238 keep reporting bugs they will be fixed swiftly, though. 1461 keep reporting bugs they will be fixed swiftly, though.
1239 1462

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