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Revision 1.119 by root, Sun Feb 22 10:13:16 2009 UTC vs.
Revision 1.156 by root, Sun Feb 21 15:37:53 2016 UTC

64so, and even documents what "correct" means. 64so, and even documents what "correct" means.
65 65
66=item * round-trip integrity 66=item * round-trip integrity
67 67
68When you serialise a perl data structure using only data types supported 68When you serialise a perl data structure using only data types supported
69by JSON, the deserialised data structure is identical on the Perl level. 69by JSON and Perl, the deserialised data structure is identical on the Perl
70(e.g. the string "2.0" doesn't suddenly become "2" just because it looks 70level. (e.g. the string "2.0" doesn't suddenly become "2" just because
71like a number). There minor I<are> exceptions to this, read the MAPPING 71it looks like a number). There I<are> minor exceptions to this, read the
72section below to learn about those. 72MAPPING section below to learn about those.
73 73
74=item * strict checking of JSON correctness 74=item * strict checking of JSON correctness
75 75
76There is no guessing, no generating of illegal JSON texts by default, 76There is no guessing, no generating of illegal JSON texts by default,
77and only JSON is accepted as input by default (the latter is a security 77and only JSON is accepted as input by default (the latter is a security
83this module usually compares favourably in terms of speed, too. 83this module usually compares favourably in terms of speed, too.
84 84
85=item * simple to use 85=item * simple to use
86 86
87This module has both a simple functional interface as well as an object 87This module has both a simple functional interface as well as an object
88oriented interface interface. 88oriented interface.
89 89
90=item * reasonably versatile output formats 90=item * reasonably versatile output formats
91 91
92You can choose between the most compact guaranteed-single-line format 92You can choose between the most compact guaranteed-single-line format
93possible (nice for simple line-based protocols), a pure-ASCII format 93possible (nice for simple line-based protocols), a pure-ASCII format
99 99
100=cut 100=cut
101 101
102package JSON::XS; 102package JSON::XS;
103 103
104no warnings; 104use common::sense;
105use strict;
106 105
107our $VERSION = '2.232'; 106our $VERSION = 3.01;
108our @ISA = qw(Exporter); 107our @ISA = qw(Exporter);
109 108
110our @EXPORT = qw(encode_json decode_json to_json from_json); 109our @EXPORT = qw(encode_json decode_json);
111
112sub to_json($) {
113 require Carp;
114 Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
115}
116
117sub from_json($) {
118 require Carp;
119 Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
120}
121 110
122use Exporter; 111use Exporter;
123use XSLoader; 112use XSLoader;
113
114use Types::Serialiser ();
124 115
125=head1 FUNCTIONAL INTERFACE 116=head1 FUNCTIONAL INTERFACE
126 117
127The following convenience methods are provided by this module. They are 118The following convenience methods are provided by this module. They are
128exported by default: 119exported by default:
149This function call is functionally identical to: 140This function call is functionally identical to:
150 141
151 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 142 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
152 143
153Except being faster. 144Except being faster.
154
155=item $is_boolean = JSON::XS::is_bool $scalar
156
157Returns true if the passed scalar represents either JSON::XS::true or
158JSON::XS::false, two constants that act like C<1> and C<0>, respectively
159and are used to represent JSON C<true> and C<false> values in Perl.
160
161See MAPPING, below, for more information on how JSON values are mapped to
162Perl.
163 145
164=back 146=back
165 147
166 148
167=head1 A FEW NOTES ON UNICODE AND PERL 149=head1 A FEW NOTES ON UNICODE AND PERL
422 [ 404 [
423 1, # this comment not allowed in JSON 405 1, # this comment not allowed in JSON
424 # neither this one... 406 # neither this one...
425 ] 407 ]
426 408
409=item * literal ASCII TAB characters in strings
410
411Literal ASCII TAB characters are now allowed in strings (and treated as
412C<\t>).
413
414 [
415 "Hello\tWorld",
416 "Hello<TAB>World", # literal <TAB> would not normally be allowed
417 ]
418
427=back 419=back
428 420
429=item $json = $json->canonical ([$enable]) 421=item $json = $json->canonical ([$enable])
430 422
431=item $enabled = $json->get_canonical 423=item $enabled = $json->get_canonical
433If C<$enable> is true (or missing), then the C<encode> method will output JSON objects 425If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
434by sorting their keys. This is adding a comparatively high overhead. 426by sorting their keys. This is adding a comparatively high overhead.
435 427
436If C<$enable> is false, then the C<encode> method will output key-value 428If C<$enable> is false, then the C<encode> method will output key-value
437pairs in the order Perl stores them (which will likely change between runs 429pairs in the order Perl stores them (which will likely change between runs
438of the same script). 430of the same script, and can change even within the same run from 5.18
431onwards).
439 432
440This option is useful if you want the same data structure to be encoded as 433This option is useful if you want the same data structure to be encoded as
441the same JSON text (given the same overall settings). If it is disabled, 434the same JSON text (given the same overall settings). If it is disabled,
442the same hash might be encoded differently even if contains the same data, 435the same hash might be encoded differently even if contains the same data,
443as key-value pairs have no inherent ordering in Perl. 436as key-value pairs have no inherent ordering in Perl.
444 437
445This setting has no effect when decoding JSON texts. 438This setting has no effect when decoding JSON texts.
439
440This setting has currently no effect on tied hashes.
446 441
447=item $json = $json->allow_nonref ([$enable]) 442=item $json = $json->allow_nonref ([$enable])
448 443
449=item $enabled = $json->get_allow_nonref 444=item $enabled = $json->get_allow_nonref
450 445
482 477
483=item $json = $json->allow_blessed ([$enable]) 478=item $json = $json->allow_blessed ([$enable])
484 479
485=item $enabled = $json->get_allow_blessed 480=item $enabled = $json->get_allow_blessed
486 481
482See L<OBJECT SERIALISATION> for details.
483
487If C<$enable> is true (or missing), then the C<encode> method will not 484If C<$enable> is true (or missing), then the C<encode> method will not
488barf when it encounters a blessed reference. Instead, the value of the 485barf when it encounters a blessed reference that it cannot convert
489B<convert_blessed> option will decide whether C<null> (C<convert_blessed> 486otherwise. Instead, a JSON C<null> value is encoded instead of the object.
490disabled or no C<TO_JSON> method found) or a representation of the
491object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
492encoded. Has no effect on C<decode>.
493 487
494If C<$enable> is false (the default), then C<encode> will throw an 488If C<$enable> is false (the default), then C<encode> will throw an
495exception when it encounters a blessed object. 489exception when it encounters a blessed object that it cannot convert
490otherwise.
491
492This setting has no effect on C<decode>.
496 493
497=item $json = $json->convert_blessed ([$enable]) 494=item $json = $json->convert_blessed ([$enable])
498 495
499=item $enabled = $json->get_convert_blessed 496=item $enabled = $json->get_convert_blessed
497
498See L<OBJECT SERIALISATION> for details.
500 499
501If C<$enable> is true (or missing), then C<encode>, upon encountering a 500If C<$enable> is true (or missing), then C<encode>, upon encountering a
502blessed object, will check for the availability of the C<TO_JSON> method 501blessed object, will check for the availability of the C<TO_JSON> method
503on the object's class. If found, it will be called in scalar context 502on the object's class. If found, it will be called in scalar context and
504and the resulting scalar will be encoded instead of the object. If no 503the resulting scalar will be encoded instead of the object.
505C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
506to do.
507 504
508The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON> 505The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
509returns other blessed objects, those will be handled in the same 506returns other blessed objects, those will be handled in the same
510way. C<TO_JSON> must take care of not causing an endless recursion cycle 507way. C<TO_JSON> must take care of not causing an endless recursion cycle
511(== crash) in this case. The name of C<TO_JSON> was chosen because other 508(== crash) in this case. The name of C<TO_JSON> was chosen because other
512methods called by the Perl core (== not by the user of the object) are 509methods called by the Perl core (== not by the user of the object) are
513usually in upper case letters and to avoid collisions with any C<to_json> 510usually in upper case letters and to avoid collisions with any C<to_json>
514function or method. 511function or method.
515 512
516This setting does not yet influence C<decode> in any way, but in the 513If C<$enable> is false (the default), then C<encode> will not consider
517future, global hooks might get installed that influence C<decode> and are 514this type of conversion.
518enabled by this setting.
519 515
520If C<$enable> is false, then the C<allow_blessed> setting will decide what 516This setting has no effect on C<decode>.
521to do when a blessed object is found. 517
518=item $json = $json->allow_tags ([$enable])
519
520=item $enabled = $json->allow_tags
521
522See L<OBJECT SERIALISATION> for details.
523
524If C<$enable> is true (or missing), then C<encode>, upon encountering a
525blessed object, will check for the availability of the C<FREEZE> method on
526the object's class. If found, it will be used to serialise the object into
527a nonstandard tagged JSON value (that JSON decoders cannot decode).
528
529It also causes C<decode> to parse such tagged JSON values and deserialise
530them via a call to the C<THAW> method.
531
532If C<$enable> is false (the default), then C<encode> will not consider
533this type of conversion, and tagged JSON values will cause a parse error
534in C<decode>, as if tags were not part of the grammar.
522 535
523=item $json = $json->filter_json_object ([$coderef->($hashref)]) 536=item $json = $json->filter_json_object ([$coderef->($hashref)])
524 537
525When C<$coderef> is specified, it will be called from C<decode> each 538When C<$coderef> is specified, it will be called from C<decode> each
526time it decodes a JSON object. The only argument is a reference to the 539time it decodes a JSON object. The only argument is a reference to the
665 678
666See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 679See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
667 680
668=item $json_text = $json->encode ($perl_scalar) 681=item $json_text = $json->encode ($perl_scalar)
669 682
670Converts the given Perl data structure (a simple scalar or a reference 683Converts the given Perl value or data structure to its JSON
671to a hash or array) to its JSON representation. Simple scalars will be 684representation. Croaks on error.
672converted into JSON string or number sequences, while references to arrays
673become JSON arrays and references to hashes become JSON objects. Undefined
674Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
675nor C<false> values will be generated.
676 685
677=item $perl_scalar = $json->decode ($json_text) 686=item $perl_scalar = $json->decode ($json_text)
678 687
679The opposite of C<encode>: expects a JSON text and tries to parse it, 688The opposite of C<encode>: expects a JSON text and tries to parse it,
680returning the resulting simple scalar or reference. Croaks on error. 689returning the resulting simple scalar or reference. Croaks on error.
681
682JSON numbers and strings become simple Perl scalars. JSON arrays become
683Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
684C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
685 690
686=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text) 691=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
687 692
688This works like the C<decode> method, but instead of raising an exception 693This works like the C<decode> method, but instead of raising an exception
689when there is trailing garbage after the first JSON object, it will 694when there is trailing garbage after the first JSON object, it will
690silently stop parsing there and return the number of characters consumed 695silently stop parsing there and return the number of characters consumed
691so far. 696so far.
692 697
693This is useful if your JSON texts are not delimited by an outer protocol 698This is useful if your JSON texts are not delimited by an outer protocol
694(which is not the brightest thing to do in the first place) and you need
695to know where the JSON text ends. 699and you need to know where the JSON text ends.
696 700
697 JSON::XS->new->decode_prefix ("[1] the tail") 701 JSON::XS->new->decode_prefix ("[1] the tail")
698 => ([], 3) 702 => ([1], 3)
699 703
700=back 704=back
701 705
702 706
703=head1 INCREMENTAL PARSING 707=head1 INCREMENTAL PARSING
712calls). 716calls).
713 717
714JSON::XS will only attempt to parse the JSON text once it is sure it 718JSON::XS will only attempt to parse the JSON text once it is sure it
715has enough text to get a decisive result, using a very simple but 719has enough text to get a decisive result, using a very simple but
716truly incremental parser. This means that it sometimes won't stop as 720truly incremental parser. This means that it sometimes won't stop as
717early as the full parser, for example, it doesn't detect parenthese 721early as the full parser, for example, it doesn't detect mismatched
718mismatches. The only thing it guarantees is that it starts decoding as 722parentheses. The only thing it guarantees is that it starts decoding as
719soon as a syntactically valid JSON text has been seen. This means you need 723soon as a syntactically valid JSON text has been seen. This means you need
720to set resource limits (e.g. C<max_size>) to ensure the parser will stop 724to set resource limits (e.g. C<max_size>) to ensure the parser will stop
721parsing in the presence if syntax errors. 725parsing in the presence if syntax errors.
722 726
723The following methods implement this incremental parser. 727The following methods implement this incremental parser.
739 743
740If the method is called in scalar context, then it will try to extract 744If the method is called in scalar context, then it will try to extract
741exactly I<one> JSON object. If that is successful, it will return this 745exactly I<one> JSON object. If that is successful, it will return this
742object, otherwise it will return C<undef>. If there is a parse error, 746object, otherwise it will return C<undef>. If there is a parse error,
743this method will croak just as C<decode> would do (one can then use 747this method will croak just as C<decode> would do (one can then use
744C<incr_skip> to skip the errornous part). This is the most common way of 748C<incr_skip> to skip the erroneous part). This is the most common way of
745using the method. 749using the method.
746 750
747And finally, in list context, it will try to extract as many objects 751And finally, in list context, it will try to extract as many objects
748from the stream as it can find and return them, or the empty list 752from the stream as it can find and return them, or the empty list
749otherwise. For this to work, there must be no separators between the JSON 753otherwise. For this to work, there must be no separators between the JSON
750objects or arrays, instead they must be concatenated back-to-back. If 754objects or arrays, instead they must be concatenated back-to-back. If
751an error occurs, an exception will be raised as in the scalar context 755an error occurs, an exception will be raised as in the scalar context
752case. Note that in this case, any previously-parsed JSON texts will be 756case. Note that in this case, any previously-parsed JSON texts will be
753lost. 757lost.
754 758
759Example: Parse some JSON arrays/objects in a given string and return
760them.
761
762 my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
763
755=item $lvalue_string = $json->incr_text 764=item $lvalue_string = $json->incr_text
756 765
757This method returns the currently stored JSON fragment as an lvalue, that 766This method returns the currently stored JSON fragment as an lvalue, that
758is, you can manipulate it. This I<only> works when a preceding call to 767is, you can manipulate it. This I<only> works when a preceding call to
759C<incr_parse> in I<scalar context> successfully returned an object. Under 768C<incr_parse> in I<scalar context> successfully returned an object. Under
773C<incr_parse> died, in which case the input buffer and incremental parser 782C<incr_parse> died, in which case the input buffer and incremental parser
774state is left unchanged, to skip the text parsed so far and to reset the 783state is left unchanged, to skip the text parsed so far and to reset the
775parse state. 784parse state.
776 785
777The difference to C<incr_reset> is that only text until the parse error 786The difference to C<incr_reset> is that only text until the parse error
778occured is removed. 787occurred is removed.
779 788
780=item $json->incr_reset 789=item $json->incr_reset
781 790
782This completely resets the incremental parser, that is, after this call, 791This completely resets the incremental parser, that is, after this call,
783it will be as if the parser had never parsed anything. 792it will be as if the parser had never parsed anything.
789=back 798=back
790 799
791=head2 LIMITATIONS 800=head2 LIMITATIONS
792 801
793All options that affect decoding are supported, except 802All options that affect decoding are supported, except
794C<allow_nonref>. The reason for this is that it cannot be made to 803C<allow_nonref>. The reason for this is that it cannot be made to work
795work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate 804sensibly: JSON objects and arrays are self-delimited, i.e. you can
796them back to back and still decode them perfectly. This does not hold true 805concatenate them back to back and still decode them perfectly. This does
797for JSON numbers, however. 806not hold true for JSON numbers, however.
798 807
799For example, is the string C<1> a single JSON number, or is it simply the 808For example, is the string C<1> a single JSON number, or is it simply the
800start of C<12>? Or is C<12> a single JSON number, or the concatenation 809start of C<12>? Or is C<12> a single JSON number, or the concatenation
801of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS 810of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
802takes the conservative route and disallows this case. 811takes the conservative route and disallows this case.
981If the number consists of digits only, JSON::XS will try to represent 990If the number consists of digits only, JSON::XS will try to represent
982it as an integer value. If that fails, it will try to represent it as 991it as an integer value. If that fails, it will try to represent it as
983a numeric (floating point) value if that is possible without loss of 992a numeric (floating point) value if that is possible without loss of
984precision. Otherwise it will preserve the number as a string value (in 993precision. Otherwise it will preserve the number as a string value (in
985which case you lose roundtripping ability, as the JSON number will be 994which case you lose roundtripping ability, as the JSON number will be
986re-encoded toa JSON string). 995re-encoded to a JSON string).
987 996
988Numbers containing a fractional or exponential part will always be 997Numbers containing a fractional or exponential part will always be
989represented as numeric (floating point) values, possibly at a loss of 998represented as numeric (floating point) values, possibly at a loss of
990precision (in which case you might lose perfect roundtripping ability, but 999precision (in which case you might lose perfect roundtripping ability, but
991the JSON number will still be re-encoded as a JSON number). 1000the JSON number will still be re-encoded as a JSON number).
992 1001
1002Note that precision is not accuracy - binary floating point values cannot
1003represent most decimal fractions exactly, and when converting from and to
1004floating point, JSON::XS only guarantees precision up to but not including
1005the least significant bit.
1006
993=item true, false 1007=item true, false
994 1008
995These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, 1009These JSON atoms become C<Types::Serialiser::true> and
996respectively. They are overloaded to act almost exactly like the numbers 1010C<Types::Serialiser::false>, respectively. They are overloaded to act
997C<1> and C<0>. You can check whether a scalar is a JSON boolean by using 1011almost exactly like the numbers C<1> and C<0>. You can check whether
998the C<JSON::XS::is_bool> function. 1012a scalar is a JSON boolean by using the C<Types::Serialiser::is_bool>
1013function (after C<use Types::Serialier>, of course).
999 1014
1000=item null 1015=item null
1001 1016
1002A JSON null atom becomes C<undef> in Perl. 1017A JSON null atom becomes C<undef> in Perl.
1018
1019=item shell-style comments (C<< # I<text> >>)
1020
1021As a nonstandard extension to the JSON syntax that is enabled by the
1022C<relaxed> setting, shell-style comments are allowed. They can start
1023anywhere outside strings and go till the end of the line.
1024
1025=item tagged values (C<< (I<tag>)I<value> >>).
1026
1027Another nonstandard extension to the JSON syntax, enabled with the
1028C<allow_tags> setting, are tagged values. In this implementation, the
1029I<tag> must be a perl package/class name encoded as a JSON string, and the
1030I<value> must be a JSON array encoding optional constructor arguments.
1031
1032See L<OBJECT SERIALISATION>, below, for details.
1003 1033
1004=back 1034=back
1005 1035
1006 1036
1007=head2 PERL -> JSON 1037=head2 PERL -> JSON
1012 1042
1013=over 4 1043=over 4
1014 1044
1015=item hash references 1045=item hash references
1016 1046
1017Perl hash references become JSON objects. As there is no inherent ordering 1047Perl hash references become JSON objects. As there is no inherent
1018in hash keys (or JSON objects), they will usually be encoded in a 1048ordering in hash keys (or JSON objects), they will usually be encoded
1019pseudo-random order that can change between runs of the same program but 1049in a pseudo-random order. JSON::XS can optionally sort the hash keys
1020stays generally the same within a single run of a program. JSON::XS can 1050(determined by the I<canonical> flag), so the same datastructure will
1021optionally sort the hash keys (determined by the I<canonical> flag), so 1051serialise to the same JSON text (given same settings and version of
1022the same datastructure will serialise to the same JSON text (given same 1052JSON::XS), but this incurs a runtime overhead and is only rarely useful,
1023settings and version of JSON::XS), but this incurs a runtime overhead 1053e.g. when you want to compare some JSON text against another for equality.
1024and is only rarely useful, e.g. when you want to compare some JSON text
1025against another for equality.
1026 1054
1027=item array references 1055=item array references
1028 1056
1029Perl array references become JSON arrays. 1057Perl array references become JSON arrays.
1030 1058
1031=item other references 1059=item other references
1032 1060
1033Other unblessed references are generally not allowed and will cause an 1061Other unblessed references are generally not allowed and will cause an
1034exception to be thrown, except for references to the integers C<0> and 1062exception to be thrown, except for references to the integers C<0> and
1035C<1>, which get turned into C<false> and C<true> atoms in JSON. You can 1063C<1>, which get turned into C<false> and C<true> atoms in JSON.
1036also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
1037 1064
1065Since C<JSON::XS> uses the boolean model from L<Types::Serialiser>, you
1066can also C<use Types::Serialiser> and then use C<Types::Serialiser::false>
1067and C<Types::Serialiser::true> to improve readability.
1068
1069 use Types::Serialiser;
1038 encode_json [\0, JSON::XS::true] # yields [false,true] 1070 encode_json [\0, Types::Serialiser::true] # yields [false,true]
1039 1071
1040=item JSON::XS::true, JSON::XS::false 1072=item Types::Serialiser::true, Types::Serialiser::false
1041 1073
1042These special values become JSON true and JSON false values, 1074These special values from the L<Types::Serialiser> module become JSON true
1043respectively. You can also use C<\1> and C<\0> directly if you want. 1075and JSON false values, respectively. You can also use C<\1> and C<\0>
1076directly if you want.
1044 1077
1045=item blessed objects 1078=item blessed objects
1046 1079
1047Blessed objects are not directly representable in JSON. See the 1080Blessed objects are not directly representable in JSON, but C<JSON::XS>
1048C<allow_blessed> and C<convert_blessed> methods on various options on 1081allows various ways of handling objects. See L<OBJECT SERIALISATION>,
1049how to deal with this: basically, you can choose between throwing an 1082below, for details.
1050exception, encoding the reference as if it weren't blessed, or provide
1051your own serialiser method.
1052 1083
1053=item simple scalars 1084=item simple scalars
1054 1085
1055Simple Perl scalars (any scalar that is not a reference) are the most 1086Simple Perl scalars (any scalar that is not a reference) are the most
1056difficult objects to encode: JSON::XS will encode undefined scalars as 1087difficult objects to encode: JSON::XS will encode undefined scalars as
1084 1115
1085You can not currently force the type in other, less obscure, ways. Tell me 1116You can not currently force the type in other, less obscure, ways. Tell me
1086if you need this capability (but don't forget to explain why it's needed 1117if you need this capability (but don't forget to explain why it's needed
1087:). 1118:).
1088 1119
1120Note that numerical precision has the same meaning as under Perl (so
1121binary to decimal conversion follows the same rules as in Perl, which
1122can differ to other languages). Also, your perl interpreter might expose
1123extensions to the floating point numbers of your platform, such as
1124infinities or NaN's - these cannot be represented in JSON, and it is an
1125error to pass those in.
1126
1089=back 1127=back
1128
1129=head2 OBJECT SERIALISATION
1130
1131As JSON cannot directly represent Perl objects, you have to choose between
1132a pure JSON representation (without the ability to deserialise the object
1133automatically again), and a nonstandard extension to the JSON syntax,
1134tagged values.
1135
1136=head3 SERIALISATION
1137
1138What happens when C<JSON::XS> encounters a Perl object depends on the
1139C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are
1140used in this order:
1141
1142=over 4
1143
1144=item 1. C<allow_tags> is enabled and the object has a C<FREEZE> method.
1145
1146In this case, C<JSON::XS> uses the L<Types::Serialiser> object
1147serialisation protocol to create a tagged JSON value, using a nonstandard
1148extension to the JSON syntax.
1149
1150This works by invoking the C<FREEZE> method on the object, with the first
1151argument being the object to serialise, and the second argument being the
1152constant string C<JSON> to distinguish it from other serialisers.
1153
1154The C<FREEZE> method can return any number of values (i.e. zero or
1155more). These values and the paclkage/classname of the object will then be
1156encoded as a tagged JSON value in the following format:
1157
1158 ("classname")[FREEZE return values...]
1159
1160e.g.:
1161
1162 ("URI")["http://www.google.com/"]
1163 ("MyDate")[2013,10,29]
1164 ("ImageData::JPEG")["Z3...VlCg=="]
1165
1166For example, the hypothetical C<My::Object> C<FREEZE> method might use the
1167objects C<type> and C<id> members to encode the object:
1168
1169 sub My::Object::FREEZE {
1170 my ($self, $serialiser) = @_;
1171
1172 ($self->{type}, $self->{id})
1173 }
1174
1175=item 2. C<convert_blessed> is enabled and the object has a C<TO_JSON> method.
1176
1177In this case, the C<TO_JSON> method of the object is invoked in scalar
1178context. It must return a single scalar that can be directly encoded into
1179JSON. This scalar replaces the object in the JSON text.
1180
1181For example, the following C<TO_JSON> method will convert all L<URI>
1182objects to JSON strings when serialised. The fatc that these values
1183originally were L<URI> objects is lost.
1184
1185 sub URI::TO_JSON {
1186 my ($uri) = @_;
1187 $uri->as_string
1188 }
1189
1190=item 3. C<allow_blessed> is enabled.
1191
1192The object will be serialised as a JSON null value.
1193
1194=item 4. none of the above
1195
1196If none of the settings are enabled or the respective methods are missing,
1197C<JSON::XS> throws an exception.
1198
1199=back
1200
1201=head3 DESERIALISATION
1202
1203For deserialisation there are only two cases to consider: either
1204nonstandard tagging was used, in which case C<allow_tags> decides,
1205or objects cannot be automatically be deserialised, in which
1206case you can use postprocessing or the C<filter_json_object> or
1207C<filter_json_single_key_object> callbacks to get some real objects our of
1208your JSON.
1209
1210This section only considers the tagged value case: I a tagged JSON object
1211is encountered during decoding and C<allow_tags> is disabled, a parse
1212error will result (as if tagged values were not part of the grammar).
1213
1214If C<allow_tags> is enabled, C<JSON::XS> will look up the C<THAW> method
1215of the package/classname used during serialisation (it will not attempt
1216to load the package as a Perl module). If there is no such method, the
1217decoding will fail with an error.
1218
1219Otherwise, the C<THAW> method is invoked with the classname as first
1220argument, the constant string C<JSON> as second argument, and all the
1221values from the JSON array (the values originally returned by the
1222C<FREEZE> method) as remaining arguments.
1223
1224The method must then return the object. While technically you can return
1225any Perl scalar, you might have to enable the C<enable_nonref> setting to
1226make that work in all cases, so better return an actual blessed reference.
1227
1228As an example, let's implement a C<THAW> function that regenerates the
1229C<My::Object> from the C<FREEZE> example earlier:
1230
1231 sub My::Object::THAW {
1232 my ($class, $serialiser, $type, $id) = @_;
1233
1234 $class->new (type => $type, id => $id)
1235 }
1090 1236
1091 1237
1092=head1 ENCODING/CODESET FLAG NOTES 1238=head1 ENCODING/CODESET FLAG NOTES
1093 1239
1094The interested reader might have seen a number of flags that signify 1240The interested reader might have seen a number of flags that signify
1119=item C<utf8> flag disabled 1265=item C<utf8> flag disabled
1120 1266
1121When C<utf8> is disabled (the default), then C<encode>/C<decode> generate 1267When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
1122and expect Unicode strings, that is, characters with high ordinal Unicode 1268and expect Unicode strings, that is, characters with high ordinal Unicode
1123values (> 255) will be encoded as such characters, and likewise such 1269values (> 255) will be encoded as such characters, and likewise such
1124characters are decoded as-is, no canges to them will be done, except 1270characters are decoded as-is, no changes to them will be done, except
1125"(re-)interpreting" them as Unicode codepoints or Unicode characters, 1271"(re-)interpreting" them as Unicode codepoints or Unicode characters,
1126respectively (to Perl, these are the same thing in strings unless you do 1272respectively (to Perl, these are the same thing in strings unless you do
1127funny/weird/dumb stuff). 1273funny/weird/dumb stuff).
1128 1274
1129This is useful when you want to do the encoding yourself (e.g. when you 1275This is useful when you want to do the encoding yourself (e.g. when you
1237well - using C<eval> naively simply I<will> cause problems. 1383well - using C<eval> naively simply I<will> cause problems.
1238 1384
1239Another problem is that some javascript implementations reserve 1385Another problem is that some javascript implementations reserve
1240some property names for their own purposes (which probably makes 1386some property names for their own purposes (which probably makes
1241them non-ECMAscript-compliant). For example, Iceweasel reserves the 1387them non-ECMAscript-compliant). For example, Iceweasel reserves the
1242C<__proto__> property name for it's own purposes. 1388C<__proto__> property name for its own purposes.
1243 1389
1244If that is a problem, you could parse try to filter the resulting JSON 1390If that is a problem, you could parse try to filter the resulting JSON
1245output for these property strings, e.g.: 1391output for these property strings, e.g.:
1246 1392
1247 $json =~ s/"__proto__"\s*:/"__proto__renamed":/g; 1393 $json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
1248 1394
1249This works because C<__proto__> is not valid outside of strings, so every 1395This works because C<__proto__> is not valid outside of strings, so every
1250occurence of C<"__proto__"\s*:> must be a string used as property name. 1396occurrence of C<"__proto__"\s*:> must be a string used as property name.
1251 1397
1252If you know of other incompatibilities, please let me know. 1398If you know of other incompatibilities, please let me know.
1253 1399
1254 1400
1255=head2 JSON and YAML 1401=head2 JSON and YAML
1267 my $yaml = $to_yaml->encode ($ref) . "\n"; 1413 my $yaml = $to_yaml->encode ($ref) . "\n";
1268 1414
1269This will I<usually> generate JSON texts that also parse as valid 1415This will I<usually> generate JSON texts that also parse as valid
1270YAML. Please note that YAML has hardcoded limits on (simple) object key 1416YAML. Please note that YAML has hardcoded limits on (simple) object key
1271lengths that JSON doesn't have and also has different and incompatible 1417lengths that JSON doesn't have and also has different and incompatible
1272unicode handling, so you should make sure that your hash keys are 1418unicode character escape syntax, so you should make sure that your hash
1273noticeably shorter than the 1024 "stream characters" YAML allows and that 1419keys are noticeably shorter than the 1024 "stream characters" YAML allows
1274you do not have characters with codepoint values outside the Unicode BMP 1420and that you do not have characters with codepoint values outside the
1275(basic multilingual page). YAML also does not allow C<\/> sequences in 1421Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
1276strings (which JSON::XS does not I<currently> generate, but other JSON 1422sequences in strings (which JSON::XS does not I<currently> generate, but
1277generators might). 1423other JSON generators might).
1278 1424
1279There might be other incompatibilities that I am not aware of (or the YAML 1425There might be other incompatibilities that I am not aware of (or the YAML
1280specification has been changed yet again - it does so quite often). In 1426specification has been changed yet again - it does so quite often). In
1281general you should not try to generate YAML with a JSON generator or vice 1427general you should not try to generate YAML with a JSON generator or vice
1282versa, or try to parse JSON with a YAML parser or vice versa: chances are 1428versa, or try to parse JSON with a YAML parser or vice versa: chances are
1301that difficult or long) and finally make YAML compatible to it, and 1447that difficult or long) and finally make YAML compatible to it, and
1302educating users about the changes, instead of spreading lies about the 1448educating users about the changes, instead of spreading lies about the
1303real compatibility for many I<years> and trying to silence people who 1449real compatibility for many I<years> and trying to silence people who
1304point out that it isn't true. 1450point out that it isn't true.
1305 1451
1452Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
1453though the incompatibilities have been documented (and are known to Brian)
1454for many years and the spec makes explicit claims that YAML is a superset
1455of JSON. It would be so easy to fix, but apparently, bullying people and
1456corrupting userdata is so much easier.
1457
1306=back 1458=back
1307 1459
1308 1460
1309=head2 SPEED 1461=head2 SPEED
1310 1462
1317a very short single-line JSON string (also available at 1469a very short single-line JSON string (also available at
1318L<http://dist.schmorp.de/misc/json/short.json>). 1470L<http://dist.schmorp.de/misc/json/short.json>).
1319 1471
1320 {"method": "handleMessage", "params": ["user1", 1472 {"method": "handleMessage", "params": ["user1",
1321 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7, 1473 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1322 true, false]} 1474 1, 0]}
1323 1475
1324It shows the number of encodes/decodes per second (JSON::XS uses 1476It shows the number of encodes/decodes per second (JSON::XS uses
1325the functional interface, while JSON::XS/2 uses the OO interface 1477the functional interface, while JSON::XS/2 uses the OO interface
1326with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables 1478with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
1327shrink). Higher is better: 1479shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
1480uses the from_json method). Higher is better:
1328 1481
1329 module | encode | decode | 1482 module | encode | decode |
1330 -----------|------------|------------| 1483 --------------|------------|------------|
1331 JSON 1.x | 4990.842 | 4088.813 | 1484 JSON::DWIW/DS | 86302.551 | 102300.098 |
1332 JSON::DWIW | 51653.990 | 71575.154 | 1485 JSON::DWIW/FJ | 86302.551 | 75983.768 |
1333 JSON::PC | 65948.176 | 74631.744 | 1486 JSON::PP | 15827.562 | 6638.658 |
1334 JSON::PP | 8931.652 | 3817.168 | 1487 JSON::Syck | 63358.066 | 47662.545 |
1335 JSON::Syck | 24877.248 | 27776.848 | 1488 JSON::XS | 511500.488 | 511500.488 |
1336 JSON::XS | 388361.481 | 227951.304 | 1489 JSON::XS/2 | 291271.111 | 388361.481 |
1337 JSON::XS/2 | 227951.304 | 218453.333 | 1490 JSON::XS/3 | 361577.931 | 361577.931 |
1338 JSON::XS/3 | 338250.323 | 218453.333 | 1491 Storable | 66788.280 | 265462.278 |
1339 Storable | 16500.016 | 135300.129 |
1340 -----------+------------+------------+ 1492 --------------+------------+------------+
1341 1493
1342That is, JSON::XS is about five times faster than JSON::DWIW on encoding, 1494That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
1343about three times faster on decoding, and over forty times faster 1495about five times faster on decoding, and over thirty to seventy times
1344than JSON, even with pretty-printing and key sorting. It also compares 1496faster than JSON's pure perl implementation. It also compares favourably
1345favourably to Storable for small amounts of data. 1497to Storable for small amounts of data.
1346 1498
1347Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1499Using a longer test string (roughly 18KB, generated from Yahoo! Locals
1348search API (L<http://dist.schmorp.de/misc/json/long.json>). 1500search API (L<http://dist.schmorp.de/misc/json/long.json>).
1349 1501
1350 module | encode | decode | 1502 module | encode | decode |
1351 -----------|------------|------------| 1503 --------------|------------|------------|
1352 JSON 1.x | 55.260 | 34.971 | 1504 JSON::DWIW/DS | 1647.927 | 2673.916 |
1353 JSON::DWIW | 825.228 | 1082.513 | 1505 JSON::DWIW/FJ | 1630.249 | 2596.128 |
1354 JSON::PC | 3571.444 | 2394.829 |
1355 JSON::PP | 210.987 | 32.574 | 1506 JSON::PP | 400.640 | 62.311 |
1356 JSON::Syck | 552.551 | 787.544 | 1507 JSON::Syck | 1481.040 | 1524.869 |
1357 JSON::XS | 5780.463 | 4854.519 | 1508 JSON::XS | 20661.596 | 9541.183 |
1358 JSON::XS/2 | 3869.998 | 4798.975 | 1509 JSON::XS/2 | 10683.403 | 9416.938 |
1359 JSON::XS/3 | 5862.880 | 4798.975 | 1510 JSON::XS/3 | 20661.596 | 9400.054 |
1360 Storable | 4445.002 | 5235.027 | 1511 Storable | 19765.806 | 10000.725 |
1361 -----------+------------+------------+ 1512 --------------+------------+------------+
1362 1513
1363Again, JSON::XS leads by far (except for Storable which non-surprisingly 1514Again, JSON::XS leads by far (except for Storable which non-surprisingly
1364decodes faster). 1515decodes a bit faster).
1365 1516
1366On large strings containing lots of high Unicode characters, some modules 1517On large strings containing lots of high Unicode characters, some modules
1367(such as JSON::PC) seem to decode faster than JSON::XS, but the result 1518(such as JSON::PC) seem to decode faster than JSON::XS, but the result
1368will be broken due to missing (or wrong) Unicode handling. Others refuse 1519will be broken due to missing (or wrong) Unicode handling. Others refuse
1369to decode or encode properly, so it was impossible to prepare a fair 1520to decode or encode properly, so it was impossible to prepare a fair
1405information you might want to make sure that exceptions thrown by JSON::XS 1556information you might want to make sure that exceptions thrown by JSON::XS
1406will not end up in front of untrusted eyes. 1557will not end up in front of untrusted eyes.
1407 1558
1408If you are using JSON::XS to return packets to consumption 1559If you are using JSON::XS to return packets to consumption
1409by JavaScript scripts in a browser you should have a look at 1560by JavaScript scripts in a browser you should have a look at
1410L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether 1561L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
1411you are vulnerable to some common attack vectors (which really are browser 1562see whether you are vulnerable to some common attack vectors (which really
1412design bugs, but it is still you who will have to deal with it, as major 1563are browser design bugs, but it is still you who will have to deal with
1413browser developers care only for features, not about getting security 1564it, as major browser developers care only for features, not about getting
1414right). 1565security right).
1566
1567
1568=head1 INTEROPERABILITY WITH OTHER MODULES
1569
1570C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean
1571constants. That means that the JSON true and false values will be
1572comaptible to true and false values of iother modules that do the same,
1573such as L<JSON::PP> and L<CBOR::XS>.
1574
1575
1576=head1 INTEROPERABILITY WITH OTHER JSON DECODERS
1577
1578As long as you only serialise data that can be directly expressed in JSON,
1579C<JSON::XS> is incapable of generating invalid JSON output (modulo bugs,
1580but C<JSON::XS> has found more bugs in the official JSON testsuite (1)
1581than the official JSON testsuite has found in C<JSON::XS> (0)).
1582
1583When you have trouble decoding JSON generated by this module using other
1584decoders, then it is very likely that you have an encoding mismatch or the
1585other decoder is broken.
1586
1587When decoding, C<JSON::XS> is strict by default and will likely catch all
1588errors. There are currently two settings that change this: C<relaxed>
1589makes C<JSON::XS> accept (but not generate) some non-standard extensions,
1590and C<allow_tags> will allow you to encode and decode Perl objects, at the
1591cost of not outputting valid JSON anymore.
1592
1593=head2 TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
1594
1595When you use C<allow_tags> to use the extended (and also nonstandard and
1596invalid) JSON syntax for serialised objects, and you still want to decode
1597the generated When you want to serialise objects, you can run a regex
1598to replace the tagged syntax by standard JSON arrays (it only works for
1599"normal" packagesnames without comma, newlines or single colons). First,
1600the readable Perl version:
1601
1602 # if your FREEZE methods return no values, you need this replace first:
1603 $json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[\s*\]/[$1]/gx;
1604
1605 # this works for non-empty constructor arg lists:
1606 $json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[/[$1,/gx;
1607
1608And here is a less readable version that is easy to adapt to other
1609languages:
1610
1611 $json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/[$1,/g;
1612
1613Here is an ECMAScript version (same regex):
1614
1615 json = json.replace (/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/g, "[$1,");
1616
1617Since this syntax converts to standard JSON arrays, it might be hard to
1618distinguish serialised objects from normal arrays. You can prepend a
1619"magic number" as first array element to reduce chances of a collision:
1620
1621 $json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;
1622
1623And after decoding the JSON text, you could walk the data
1624structure looking for arrays with a first element of
1625C<XU1peReLzT4ggEllLanBYq4G9VzliwKF>.
1626
1627The same approach can be used to create the tagged format with another
1628encoder. First, you create an array with the magic string as first member,
1629the classname as second, and constructor arguments last, encode it as part
1630of your JSON structure, and then:
1631
1632 $json =~ s/\[\s*"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s*,\s*("([^\\":,]+|\\.|::)*")\s*,/($1)[/g;
1633
1634Again, this has some limitations - the magic string must not be encoded
1635with character escapes, and the constructor arguments must be non-empty.
1636
1637
1638=head1 RFC7159
1639
1640Since this module was written, Google has written a new JSON RFC, RFC 7159
1641(and RFC7158). Unfortunately, this RFC breaks compatibility with both the
1642original JSON specification on www.json.org and RFC4627.
1643
1644As far as I can see, you can get partial compatibility when parsing by
1645using C<< ->allow_nonref >>. However, consider thew security implications
1646of doing so.
1647
1648I haven't decided yet when to break compatibility with RFC4627 by default
1649(and potentially leave applications insecure) and change the default to
1650follow RFC7159, but application authors are well advised to call C<<
1651->allow_nonref(0) >> even if this is the current default, if they cannot
1652handle non-reference values, in preparation for the day when the4 default
1653will change.
1415 1654
1416 1655
1417=head1 THREADS 1656=head1 THREADS
1418 1657
1419This module is I<not> guaranteed to be thread safe and there are no 1658This module is I<not> guaranteed to be thread safe and there are no
1422process simulations - use fork, it's I<much> faster, cheaper, better). 1661process simulations - use fork, it's I<much> faster, cheaper, better).
1423 1662
1424(It might actually work, but you have been warned). 1663(It might actually work, but you have been warned).
1425 1664
1426 1665
1666=head1 THE PERILS OF SETLOCALE
1667
1668Sometimes people avoid the Perl locale support and directly call the
1669system's setlocale function with C<LC_ALL>.
1670
1671This breaks both perl and modules such as JSON::XS, as stringification of
1672numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
1673print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
1674perl to stringify numbers).
1675
1676The solution is simple: don't call C<setlocale>, or use it for only those
1677categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
1678
1679If you need C<LC_NUMERIC>, you should enable it only around the code that
1680actually needs it (avoiding stringification of numbers), and restore it
1681afterwards.
1682
1683
1427=head1 BUGS 1684=head1 BUGS
1428 1685
1429While the goal of this module is to be correct, that unfortunately does 1686While the goal of this module is to be correct, that unfortunately does
1430not mean it's bug-free, only that I think its design is bug-free. If you 1687not mean it's bug-free, only that I think its design is bug-free. If you
1431keep reporting bugs they will be fixed swiftly, though. 1688keep reporting bugs they will be fixed swiftly, though.
1433Please refrain from using rt.cpan.org or any other bug reporting 1690Please refrain from using rt.cpan.org or any other bug reporting
1434service. I put the contact address into my modules for a reason. 1691service. I put the contact address into my modules for a reason.
1435 1692
1436=cut 1693=cut
1437 1694
1438our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" }; 1695BEGIN {
1439our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" }; 1696 *true = \$Types::Serialiser::true;
1697 *true = \&Types::Serialiser::true;
1698 *false = \$Types::Serialiser::false;
1699 *false = \&Types::Serialiser::false;
1700 *is_bool = \&Types::Serialiser::is_bool;
1440 1701
1441sub true() { $true } 1702 *JSON::XS::Boolean:: = *Types::Serialiser::Boolean::;
1442sub false() { $false }
1443
1444sub is_bool($) {
1445 UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
1446# or UNIVERSAL::isa $_[0], "JSON::Literal"
1447} 1703}
1448 1704
1449XSLoader::load "JSON::XS", $VERSION; 1705XSLoader::load "JSON::XS", $VERSION;
1450
1451package JSON::XS::Boolean;
1452
1453use overload
1454 "0+" => sub { ${$_[0]} },
1455 "++" => sub { $_[0] = ${$_[0]} + 1 },
1456 "--" => sub { $_[0] = ${$_[0]} - 1 },
1457 fallback => 1;
1458
14591;
1460 1706
1461=head1 SEE ALSO 1707=head1 SEE ALSO
1462 1708
1463The F<json_xs> command line utility for quick experiments. 1709The F<json_xs> command line utility for quick experiments.
1464 1710
1467 Marc Lehmann <schmorp@schmorp.de> 1713 Marc Lehmann <schmorp@schmorp.de>
1468 http://home.schmorp.de/ 1714 http://home.schmorp.de/
1469 1715
1470=cut 1716=cut
1471 1717
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1719

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