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Revision 1.130 by root, Thu Mar 11 17:36:09 2010 UTC vs.
Revision 1.151 by root, Tue Oct 29 15:55:49 2013 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
101 101
102package JSON::XS; 102package JSON::XS;
103 103
104use common::sense; 104use common::sense;
105 105
106our $VERSION = '2.28'; 106our $VERSION = 3.01;
107our @ISA = qw(Exporter); 107our @ISA = qw(Exporter);
108 108
109our @EXPORT = qw(encode_json decode_json to_json from_json); 109our @EXPORT = qw(encode_json decode_json);
110
111sub to_json($) {
112 require Carp;
113 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");
114}
115
116sub from_json($) {
117 require Carp;
118 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");
119}
120 110
121use Exporter; 111use Exporter;
122use XSLoader; 112use XSLoader;
113
114use Types::Serialiser ();
123 115
124=head1 FUNCTIONAL INTERFACE 116=head1 FUNCTIONAL INTERFACE
125 117
126The following convenience methods are provided by this module. They are 118The following convenience methods are provided by this module. They are
127exported by default: 119exported by default:
148This function call is functionally identical to: 140This function call is functionally identical to:
149 141
150 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 142 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
151 143
152Except being faster. 144Except being faster.
153
154=item $is_boolean = JSON::XS::is_bool $scalar
155
156Returns true if the passed scalar represents either JSON::XS::true or
157JSON::XS::false, two constants that act like C<1> and C<0>, respectively
158and are used to represent JSON C<true> and C<false> values in Perl.
159
160See MAPPING, below, for more information on how JSON values are mapped to
161Perl.
162 145
163=back 146=back
164 147
165 148
166=head1 A FEW NOTES ON UNICODE AND PERL 149=head1 A FEW NOTES ON UNICODE AND PERL
432If C<$enable> is true (or missing), then the C<encode> method will output JSON objects 415If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
433by sorting their keys. This is adding a comparatively high overhead. 416by sorting their keys. This is adding a comparatively high overhead.
434 417
435If C<$enable> is false, then the C<encode> method will output key-value 418If C<$enable> is false, then the C<encode> method will output key-value
436pairs in the order Perl stores them (which will likely change between runs 419pairs in the order Perl stores them (which will likely change between runs
437of the same script). 420of the same script, and can change even within the same run from 5.18
421onwards).
438 422
439This option is useful if you want the same data structure to be encoded as 423This option is useful if you want the same data structure to be encoded as
440the same JSON text (given the same overall settings). If it is disabled, 424the same JSON text (given the same overall settings). If it is disabled,
441the same hash might be encoded differently even if contains the same data, 425the same hash might be encoded differently even if contains the same data,
442as key-value pairs have no inherent ordering in Perl. 426as key-value pairs have no inherent ordering in Perl.
483 467
484=item $json = $json->allow_blessed ([$enable]) 468=item $json = $json->allow_blessed ([$enable])
485 469
486=item $enabled = $json->get_allow_blessed 470=item $enabled = $json->get_allow_blessed
487 471
472See L<OBJECT SERIALISATION> for details.
473
488If C<$enable> is true (or missing), then the C<encode> method will not 474If C<$enable> is true (or missing), then the C<encode> method will not
489barf when it encounters a blessed reference. Instead, the value of the 475barf when it encounters a blessed reference that it cannot convert
490B<convert_blessed> option will decide whether C<null> (C<convert_blessed> 476otherwise. Instead, a JSON C<null> value is encoded instead of the object.
491disabled or no C<TO_JSON> method found) or a representation of the
492object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
493encoded. Has no effect on C<decode>.
494 477
495If C<$enable> is false (the default), then C<encode> will throw an 478If C<$enable> is false (the default), then C<encode> will throw an
496exception when it encounters a blessed object. 479exception when it encounters a blessed object that it cannot convert
480otherwise.
481
482This setting has no effect on C<decode>.
497 483
498=item $json = $json->convert_blessed ([$enable]) 484=item $json = $json->convert_blessed ([$enable])
499 485
500=item $enabled = $json->get_convert_blessed 486=item $enabled = $json->get_convert_blessed
487
488See L<OBJECT SERIALISATION> for details.
501 489
502If C<$enable> is true (or missing), then C<encode>, upon encountering a 490If C<$enable> is true (or missing), then C<encode>, upon encountering a
503blessed object, will check for the availability of the C<TO_JSON> method 491blessed object, will check for the availability of the C<TO_JSON> method
504on the object's class. If found, it will be called in scalar context 492on the object's class. If found, it will be called in scalar context and
505and the resulting scalar will be encoded instead of the object. If no 493the resulting scalar will be encoded instead of the object.
506C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
507to do.
508 494
509The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON> 495The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
510returns other blessed objects, those will be handled in the same 496returns other blessed objects, those will be handled in the same
511way. C<TO_JSON> must take care of not causing an endless recursion cycle 497way. C<TO_JSON> must take care of not causing an endless recursion cycle
512(== crash) in this case. The name of C<TO_JSON> was chosen because other 498(== crash) in this case. The name of C<TO_JSON> was chosen because other
513methods called by the Perl core (== not by the user of the object) are 499methods called by the Perl core (== not by the user of the object) are
514usually in upper case letters and to avoid collisions with any C<to_json> 500usually in upper case letters and to avoid collisions with any C<to_json>
515function or method. 501function or method.
516 502
517This setting does not yet influence C<decode> in any way, but in the 503If C<$enable> is false (the default), then C<encode> will not consider
518future, global hooks might get installed that influence C<decode> and are 504this type of conversion.
519enabled by this setting.
520 505
521If C<$enable> is false, then the C<allow_blessed> setting will decide what 506This setting has no effect on C<decode>.
522to do when a blessed object is found. 507
508=item $json = $json->allow_tags ([$enable])
509
510=item $enabled = $json->allow_tags
511
512See L<OBJECT SERIALISATION> for details.
513
514If C<$enable> is true (or missing), then C<encode>, upon encountering a
515blessed object, will check for the availability of the C<FREEZE> method on
516the object's class. If found, it will be used to serialise the object into
517a nonstandard tagged JSON value (that JSON decoders cannot decode).
518
519It also causes C<decode> to parse such tagged JSON values and deserialise
520them via a call to the C<THAW> method.
521
522If C<$enable> is false (the default), then C<encode> will not consider
523this type of conversion, and tagged JSON values will cause a parse error
524in C<decode>, as if tags were not part of the grammar.
523 525
524=item $json = $json->filter_json_object ([$coderef->($hashref)]) 526=item $json = $json->filter_json_object ([$coderef->($hashref)])
525 527
526When C<$coderef> is specified, it will be called from C<decode> each 528When C<$coderef> is specified, it will be called from C<decode> each
527time it decodes a JSON object. The only argument is a reference to the 529time it decodes a JSON object. The only argument is a reference to the
666 668
667See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 669See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
668 670
669=item $json_text = $json->encode ($perl_scalar) 671=item $json_text = $json->encode ($perl_scalar)
670 672
671Converts the given Perl data structure (a simple scalar or a reference 673Converts the given Perl value or data structure to its JSON
672to a hash or array) to its JSON representation. Simple scalars will be 674representation. Croaks on error.
673converted into JSON string or number sequences, while references to arrays
674become JSON arrays and references to hashes become JSON objects. Undefined
675Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
676nor C<false> values will be generated.
677 675
678=item $perl_scalar = $json->decode ($json_text) 676=item $perl_scalar = $json->decode ($json_text)
679 677
680The opposite of C<encode>: expects a JSON text and tries to parse it, 678The opposite of C<encode>: expects a JSON text and tries to parse it,
681returning the resulting simple scalar or reference. Croaks on error. 679returning the resulting simple scalar or reference. Croaks on error.
682
683JSON numbers and strings become simple Perl scalars. JSON arrays become
684Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
685C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
686 680
687=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text) 681=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
688 682
689This works like the C<decode> method, but instead of raising an exception 683This works like the C<decode> method, but instead of raising an exception
690when there is trailing garbage after the first JSON object, it will 684when there is trailing garbage after the first JSON object, it will
691silently stop parsing there and return the number of characters consumed 685silently stop parsing there and return the number of characters consumed
692so far. 686so far.
693 687
694This is useful if your JSON texts are not delimited by an outer protocol 688This is useful if your JSON texts are not delimited by an outer protocol
695(which is not the brightest thing to do in the first place) and you need
696to know where the JSON text ends. 689and you need to know where the JSON text ends.
697 690
698 JSON::XS->new->decode_prefix ("[1] the tail") 691 JSON::XS->new->decode_prefix ("[1] the tail")
699 => ([], 3) 692 => ([], 3)
700 693
701=back 694=back
713calls). 706calls).
714 707
715JSON::XS will only attempt to parse the JSON text once it is sure it 708JSON::XS will only attempt to parse the JSON text once it is sure it
716has enough text to get a decisive result, using a very simple but 709has enough text to get a decisive result, using a very simple but
717truly incremental parser. This means that it sometimes won't stop as 710truly incremental parser. This means that it sometimes won't stop as
718early as the full parser, for example, it doesn't detect parenthese 711early as the full parser, for example, it doesn't detect mismatched
719mismatches. The only thing it guarantees is that it starts decoding as 712parentheses. The only thing it guarantees is that it starts decoding as
720soon as a syntactically valid JSON text has been seen. This means you need 713soon as a syntactically valid JSON text has been seen. This means you need
721to set resource limits (e.g. C<max_size>) to ensure the parser will stop 714to set resource limits (e.g. C<max_size>) to ensure the parser will stop
722parsing in the presence if syntax errors. 715parsing in the presence if syntax errors.
723 716
724The following methods implement this incremental parser. 717The following methods implement this incremental parser.
740 733
741If the method is called in scalar context, then it will try to extract 734If the method is called in scalar context, then it will try to extract
742exactly I<one> JSON object. If that is successful, it will return this 735exactly I<one> JSON object. If that is successful, it will return this
743object, otherwise it will return C<undef>. If there is a parse error, 736object, otherwise it will return C<undef>. If there is a parse error,
744this method will croak just as C<decode> would do (one can then use 737this method will croak just as C<decode> would do (one can then use
745C<incr_skip> to skip the errornous part). This is the most common way of 738C<incr_skip> to skip the erroneous part). This is the most common way of
746using the method. 739using the method.
747 740
748And finally, in list context, it will try to extract as many objects 741And finally, in list context, it will try to extract as many objects
749from the stream as it can find and return them, or the empty list 742from the stream as it can find and return them, or the empty list
750otherwise. For this to work, there must be no separators between the JSON 743otherwise. For this to work, there must be no separators between the JSON
779C<incr_parse> died, in which case the input buffer and incremental parser 772C<incr_parse> died, in which case the input buffer and incremental parser
780state is left unchanged, to skip the text parsed so far and to reset the 773state is left unchanged, to skip the text parsed so far and to reset the
781parse state. 774parse state.
782 775
783The difference to C<incr_reset> is that only text until the parse error 776The difference to C<incr_reset> is that only text until the parse error
784occured is removed. 777occurred is removed.
785 778
786=item $json->incr_reset 779=item $json->incr_reset
787 780
788This completely resets the incremental parser, that is, after this call, 781This completely resets the incremental parser, that is, after this call,
789it will be as if the parser had never parsed anything. 782it will be as if the parser had never parsed anything.
795=back 788=back
796 789
797=head2 LIMITATIONS 790=head2 LIMITATIONS
798 791
799All options that affect decoding are supported, except 792All options that affect decoding are supported, except
800C<allow_nonref>. The reason for this is that it cannot be made to 793C<allow_nonref>. The reason for this is that it cannot be made to work
801work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate 794sensibly: JSON objects and arrays are self-delimited, i.e. you can
802them back to back and still decode them perfectly. This does not hold true 795concatenate them back to back and still decode them perfectly. This does
803for JSON numbers, however. 796not hold true for JSON numbers, however.
804 797
805For example, is the string C<1> a single JSON number, or is it simply the 798For example, is the string C<1> a single JSON number, or is it simply the
806start of C<12>? Or is C<12> a single JSON number, or the concatenation 799start of C<12>? Or is C<12> a single JSON number, or the concatenation
807of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS 800of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
808takes the conservative route and disallows this case. 801takes the conservative route and disallows this case.
987If the number consists of digits only, JSON::XS will try to represent 980If the number consists of digits only, JSON::XS will try to represent
988it as an integer value. If that fails, it will try to represent it as 981it as an integer value. If that fails, it will try to represent it as
989a numeric (floating point) value if that is possible without loss of 982a numeric (floating point) value if that is possible without loss of
990precision. Otherwise it will preserve the number as a string value (in 983precision. Otherwise it will preserve the number as a string value (in
991which case you lose roundtripping ability, as the JSON number will be 984which case you lose roundtripping ability, as the JSON number will be
992re-encoded toa JSON string). 985re-encoded to a JSON string).
993 986
994Numbers containing a fractional or exponential part will always be 987Numbers containing a fractional or exponential part will always be
995represented as numeric (floating point) values, possibly at a loss of 988represented as numeric (floating point) values, possibly at a loss of
996precision (in which case you might lose perfect roundtripping ability, but 989precision (in which case you might lose perfect roundtripping ability, but
997the JSON number will still be re-encoded as a JSON number). 990the JSON number will still be re-encoded as a JSON number).
998 991
992Note that precision is not accuracy - binary floating point values cannot
993represent most decimal fractions exactly, and when converting from and to
994floating point, JSON::XS only guarantees precision up to but not including
995the least significant bit.
996
999=item true, false 997=item true, false
1000 998
1001These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, 999These JSON atoms become C<Types::Serialiser::true> and
1002respectively. They are overloaded to act almost exactly like the numbers 1000C<Types::Serialiser::false>, respectively. They are overloaded to act
1003C<1> and C<0>. You can check whether a scalar is a JSON boolean by using 1001almost exactly like the numbers C<1> and C<0>. You can check whether
1004the C<JSON::XS::is_bool> function. 1002a scalar is a JSON boolean by using the C<Types::Serialiser::is_bool>
1003function (after C<use Types::Serialier>, of course).
1005 1004
1006=item null 1005=item null
1007 1006
1008A JSON null atom becomes C<undef> in Perl. 1007A JSON null atom becomes C<undef> in Perl.
1008
1009=item shell-style comments (C<< # I<text> >>)
1010
1011As a nonstandard extension to the JSON syntax that is enabled by the
1012C<relaxed> setting, shell-style comments are allowed. They can start
1013anywhere outside strings and go till the end of the line.
1014
1015=item tagged values (C<< (I<tag>)I<value> >>).
1016
1017Another nonstandard extension to the JSON syntax, enabled with the
1018C<allow_tags> setting, are tagged values. In this implementation, the
1019I<tag> must be a perl package/class name encoded as a JSON string, and the
1020I<value> must be a JSON array encoding optional constructor arguments.
1021
1022See L<OBJECT SERIALISATION>, below, for details.
1009 1023
1010=back 1024=back
1011 1025
1012 1026
1013=head2 PERL -> JSON 1027=head2 PERL -> JSON
1018 1032
1019=over 4 1033=over 4
1020 1034
1021=item hash references 1035=item hash references
1022 1036
1023Perl hash references become JSON objects. As there is no inherent ordering 1037Perl hash references become JSON objects. As there is no inherent
1024in hash keys (or JSON objects), they will usually be encoded in a 1038ordering in hash keys (or JSON objects), they will usually be encoded
1025pseudo-random order that can change between runs of the same program but 1039in a pseudo-random order. JSON::XS can optionally sort the hash keys
1026stays generally the same within a single run of a program. JSON::XS can 1040(determined by the I<canonical> flag), so the same datastructure will
1027optionally sort the hash keys (determined by the I<canonical> flag), so 1041serialise to the same JSON text (given same settings and version of
1028the same datastructure will serialise to the same JSON text (given same 1042JSON::XS), but this incurs a runtime overhead and is only rarely useful,
1029settings and version of JSON::XS), but this incurs a runtime overhead 1043e.g. when you want to compare some JSON text against another for equality.
1030and is only rarely useful, e.g. when you want to compare some JSON text
1031against another for equality.
1032 1044
1033=item array references 1045=item array references
1034 1046
1035Perl array references become JSON arrays. 1047Perl array references become JSON arrays.
1036 1048
1037=item other references 1049=item other references
1038 1050
1039Other unblessed references are generally not allowed and will cause an 1051Other unblessed references are generally not allowed and will cause an
1040exception to be thrown, except for references to the integers C<0> and 1052exception to be thrown, except for references to the integers C<0> and
1041C<1>, which get turned into C<false> and C<true> atoms in JSON. You can 1053C<1>, which get turned into C<false> and C<true> atoms in JSON.
1042also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
1043 1054
1055Since C<JSON::XS> uses the boolean model from L<Types::Serialiser>, you
1056can also C<use Types::Serialiser> and then use C<Types::Serialiser::false>
1057and C<Types::Serialiser::true> to improve readability.
1058
1059 use Types::Serialiser;
1044 encode_json [\0, JSON::XS::true] # yields [false,true] 1060 encode_json [\0, Types::Serialiser::true] # yields [false,true]
1045 1061
1046=item JSON::XS::true, JSON::XS::false 1062=item Types::Serialiser::true, Types::Serialiser::false
1047 1063
1048These special values become JSON true and JSON false values, 1064These special values from the L<Types::Serialiser> module become JSON true
1049respectively. You can also use C<\1> and C<\0> directly if you want. 1065and JSON false values, respectively. You can also use C<\1> and C<\0>
1066directly if you want.
1050 1067
1051=item blessed objects 1068=item blessed objects
1052 1069
1053Blessed objects are not directly representable in JSON. See the 1070Blessed objects are not directly representable in JSON, but C<JSON::XS>
1054C<allow_blessed> and C<convert_blessed> methods on various options on 1071allows various ways of handling objects. See L<OBJECT SERIALISATION>,
1055how to deal with this: basically, you can choose between throwing an 1072below, for details.
1056exception, encoding the reference as if it weren't blessed, or provide
1057your own serialiser method.
1058 1073
1059=item simple scalars 1074=item simple scalars
1060 1075
1061Simple Perl scalars (any scalar that is not a reference) are the most 1076Simple Perl scalars (any scalar that is not a reference) are the most
1062difficult objects to encode: JSON::XS will encode undefined scalars as 1077difficult objects to encode: JSON::XS will encode undefined scalars as
1090 1105
1091You can not currently force the type in other, less obscure, ways. Tell me 1106You can not currently force the type in other, less obscure, ways. Tell me
1092if you need this capability (but don't forget to explain why it's needed 1107if you need this capability (but don't forget to explain why it's needed
1093:). 1108:).
1094 1109
1110Note that numerical precision has the same meaning as under Perl (so
1111binary to decimal conversion follows the same rules as in Perl, which
1112can differ to other languages). Also, your perl interpreter might expose
1113extensions to the floating point numbers of your platform, such as
1114infinities or NaN's - these cannot be represented in JSON, and it is an
1115error to pass those in.
1116
1095=back 1117=back
1118
1119=head2 OBJECT SERIALISATION
1120
1121As JSON cannot directly represent Perl objects, you have to choose between
1122a pure JSON representation (without the ability to deserialise the object
1123automatically again), and a nonstandard extension to the JSON syntax,
1124tagged values.
1125
1126=head3 SERIALISATION
1127
1128What happens when C<JSON::XS> encounters a Perl object depends on the
1129C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are
1130used in this order:
1131
1132=over 4
1133
1134=item 1. C<allow_tags> is enabled and the object has a C<FREEZE> method.
1135
1136In this case, C<JSON::XS> uses the L<Types::Serialiser> object
1137serialisation protocol to create a tagged JSON value, using a nonstandard
1138extension to the JSON syntax.
1139
1140This works by invoking the C<FREEZE> method on the object, with the first
1141argument being the object to serialise, and the second argument being the
1142constant string C<JSON> to distinguish it from other serialisers.
1143
1144The C<FREEZE> method can return any number of values (i.e. zero or
1145more). These values and the paclkage/classname of the object will then be
1146encoded as a tagged JSON value in the following format:
1147
1148 ("classname")[FREEZE return values...]
1149
1150e.g.:
1151
1152 ("URI")["http://www.google.com/"]
1153 ("MyDate")[2013,10,29]
1154 ("ImageData::JPEG")["Z3...VlCg=="]
1155
1156For example, the hypothetical C<My::Object> C<FREEZE> method might use the
1157objects C<type> and C<id> members to encode the object:
1158
1159 sub My::Object::FREEZE {
1160 my ($self, $serialiser) = @_;
1161
1162 ($self->{type}, $self->{id})
1163 }
1164
1165=item 2. C<convert_blessed> is enabled and the object has a C<TO_JSON> method.
1166
1167In this case, the C<TO_JSON> method of the object is invoked in scalar
1168context. It must return a single scalar that can be directly encoded into
1169JSON. This scalar replaces the object in the JSON text.
1170
1171For example, the following C<TO_JSON> method will convert all L<URI>
1172objects to JSON strings when serialised. The fatc that these values
1173originally were L<URI> objects is lost.
1174
1175 sub URI::TO_JSON {
1176 my ($uri) = @_;
1177 $uri->as_string
1178 }
1179
1180=item 3. C<allow_blessed> is enabled.
1181
1182The object will be serialised as a JSON null value.
1183
1184=item 4. none of the above
1185
1186If none of the settings are enabled or the respective methods are missing,
1187C<JSON::XS> throws an exception.
1188
1189=back
1190
1191=head3 DESERIALISATION
1192
1193For deserialisation there are only two cases to consider: either
1194nonstandard tagging was used, in which case C<allow_tags> decides,
1195or objects cannot be automatically be deserialised, in which
1196case you can use postprocessing or the C<filter_json_object> or
1197C<filter_json_single_key_object> callbacks to get some real objects our of
1198your JSON.
1199
1200This section only considers the tagged value case: I a tagged JSON object
1201is encountered during decoding and C<allow_tags> is disabled, a parse
1202error will result (as if tagged values were not part of the grammar).
1203
1204If C<allow_tags> is enabled, C<JSON::XS> will look up the C<THAW> method
1205of the package/classname used during serialisation (it will not attempt
1206to load the package as a Perl module). If there is no such method, the
1207decoding will fail with an error.
1208
1209Otherwise, the C<THAW> method is invoked with the classname as first
1210argument, the constant string C<JSON> as second argument, and all the
1211values from the JSON array (the values originally returned by the
1212C<FREEZE> method) as remaining arguments.
1213
1214The method must then return the object. While technically you can return
1215any Perl scalar, you might have to enable the C<enable_nonref> setting to
1216make that work in all cases, so better return an actual blessed reference.
1217
1218As an example, let's implement a C<THAW> function that regenerates the
1219C<My::Object> from the C<FREEZE> example earlier:
1220
1221 sub My::Object::THAW {
1222 my ($class, $serialiser, $type, $id) = @_;
1223
1224 $class->new (type => $type, id => $id)
1225 }
1096 1226
1097 1227
1098=head1 ENCODING/CODESET FLAG NOTES 1228=head1 ENCODING/CODESET FLAG NOTES
1099 1229
1100The interested reader might have seen a number of flags that signify 1230The interested reader might have seen a number of flags that signify
1125=item C<utf8> flag disabled 1255=item C<utf8> flag disabled
1126 1256
1127When C<utf8> is disabled (the default), then C<encode>/C<decode> generate 1257When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
1128and expect Unicode strings, that is, characters with high ordinal Unicode 1258and expect Unicode strings, that is, characters with high ordinal Unicode
1129values (> 255) will be encoded as such characters, and likewise such 1259values (> 255) will be encoded as such characters, and likewise such
1130characters are decoded as-is, no canges to them will be done, except 1260characters are decoded as-is, no changes to them will be done, except
1131"(re-)interpreting" them as Unicode codepoints or Unicode characters, 1261"(re-)interpreting" them as Unicode codepoints or Unicode characters,
1132respectively (to Perl, these are the same thing in strings unless you do 1262respectively (to Perl, these are the same thing in strings unless you do
1133funny/weird/dumb stuff). 1263funny/weird/dumb stuff).
1134 1264
1135This is useful when you want to do the encoding yourself (e.g. when you 1265This is useful when you want to do the encoding yourself (e.g. when you
1243well - using C<eval> naively simply I<will> cause problems. 1373well - using C<eval> naively simply I<will> cause problems.
1244 1374
1245Another problem is that some javascript implementations reserve 1375Another problem is that some javascript implementations reserve
1246some property names for their own purposes (which probably makes 1376some property names for their own purposes (which probably makes
1247them non-ECMAscript-compliant). For example, Iceweasel reserves the 1377them non-ECMAscript-compliant). For example, Iceweasel reserves the
1248C<__proto__> property name for it's own purposes. 1378C<__proto__> property name for its own purposes.
1249 1379
1250If that is a problem, you could parse try to filter the resulting JSON 1380If that is a problem, you could parse try to filter the resulting JSON
1251output for these property strings, e.g.: 1381output for these property strings, e.g.:
1252 1382
1253 $json =~ s/"__proto__"\s*:/"__proto__renamed":/g; 1383 $json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
1254 1384
1255This works because C<__proto__> is not valid outside of strings, so every 1385This works because C<__proto__> is not valid outside of strings, so every
1256occurence of C<"__proto__"\s*:> must be a string used as property name. 1386occurrence of C<"__proto__"\s*:> must be a string used as property name.
1257 1387
1258If you know of other incompatibilities, please let me know. 1388If you know of other incompatibilities, please let me know.
1259 1389
1260 1390
1261=head2 JSON and YAML 1391=head2 JSON and YAML
1307that difficult or long) and finally make YAML compatible to it, and 1437that difficult or long) and finally make YAML compatible to it, and
1308educating users about the changes, instead of spreading lies about the 1438educating users about the changes, instead of spreading lies about the
1309real compatibility for many I<years> and trying to silence people who 1439real compatibility for many I<years> and trying to silence people who
1310point out that it isn't true. 1440point out that it isn't true.
1311 1441
1312Addendum/2009: the YAML 1.2 spec is still incomaptible with JSON, even 1442Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
1313though the incompatibilities have been documented (and are known to 1443though the incompatibilities have been documented (and are known to Brian)
1314Brian) for many years and the spec makes explicit claims that YAML is a 1444for many years and the spec makes explicit claims that YAML is a superset
1315superset of JSON. It would be so easy to fix, but apparently, bullying and 1445of JSON. It would be so easy to fix, but apparently, bullying people and
1316corrupting userdata is so much easier. 1446corrupting userdata is so much easier.
1317 1447
1318=back 1448=back
1319 1449
1320 1450
1423are browser design bugs, but it is still you who will have to deal with 1553are browser design bugs, but it is still you who will have to deal with
1424it, as major browser developers care only for features, not about getting 1554it, as major browser developers care only for features, not about getting
1425security right). 1555security right).
1426 1556
1427 1557
1558=head1 INTEROPERABILITY WITH OTHER MODULES
1559
1560C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean
1561constants. That means that the JSON true and false values will be
1562comaptible to true and false values of iother modules that do the same,
1563such as L<JSON::PP> and L<CBOR::XS>.
1564
1565
1428=head1 THREADS 1566=head1 THREADS
1429 1567
1430This module is I<not> guaranteed to be thread safe and there are no 1568This module is I<not> guaranteed to be thread safe and there are no
1431plans to change this until Perl gets thread support (as opposed to the 1569plans to change this until Perl gets thread support (as opposed to the
1432horribly slow so-called "threads" which are simply slow and bloated 1570horribly slow so-called "threads" which are simply slow and bloated
1433process simulations - use fork, it's I<much> faster, cheaper, better). 1571process simulations - use fork, it's I<much> faster, cheaper, better).
1434 1572
1435(It might actually work, but you have been warned). 1573(It might actually work, but you have been warned).
1436 1574
1437 1575
1576=head1 THE PERILS OF SETLOCALE
1577
1578Sometimes people avoid the Perl locale support and directly call the
1579system's setlocale function with C<LC_ALL>.
1580
1581This breaks both perl and modules such as JSON::XS, as stringification of
1582numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
1583print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
1584perl to stringify numbers).
1585
1586The solution is simple: don't call C<setlocale>, or use it for only those
1587categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
1588
1589If you need C<LC_NUMERIC>, you should enable it only around the code that
1590actually needs it (avoiding stringification of numbers), and restore it
1591afterwards.
1592
1593
1438=head1 BUGS 1594=head1 BUGS
1439 1595
1440While the goal of this module is to be correct, that unfortunately does 1596While the goal of this module is to be correct, that unfortunately does
1441not mean it's bug-free, only that I think its design is bug-free. If you 1597not mean it's bug-free, only that I think its design is bug-free. If you
1442keep reporting bugs they will be fixed swiftly, though. 1598keep reporting bugs they will be fixed swiftly, though.
1444Please refrain from using rt.cpan.org or any other bug reporting 1600Please refrain from using rt.cpan.org or any other bug reporting
1445service. I put the contact address into my modules for a reason. 1601service. I put the contact address into my modules for a reason.
1446 1602
1447=cut 1603=cut
1448 1604
1449our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" }; 1605BEGIN {
1450our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" }; 1606 *true = \$Types::Serialiser::true;
1607 *true = \&Types::Serialiser::true;
1608 *false = \$Types::Serialiser::false;
1609 *false = \&Types::Serialiser::false;
1610 *is_bool = \&Types::Serialiser::is_bool;
1451 1611
1452sub true() { $true } 1612 *JSON::XS::Boolean:: = *Types::Serialiser::Boolean::;
1453sub false() { $false }
1454
1455sub is_bool($) {
1456 UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
1457# or UNIVERSAL::isa $_[0], "JSON::Literal"
1458} 1613}
1459 1614
1460XSLoader::load "JSON::XS", $VERSION; 1615XSLoader::load "JSON::XS", $VERSION;
1461
1462package JSON::XS::Boolean;
1463
1464use overload
1465 "0+" => sub { ${$_[0]} },
1466 "++" => sub { $_[0] = ${$_[0]} + 1 },
1467 "--" => sub { $_[0] = ${$_[0]} - 1 },
1468 fallback => 1;
1469
14701;
1471 1616
1472=head1 SEE ALSO 1617=head1 SEE ALSO
1473 1618
1474The F<json_xs> command line utility for quick experiments. 1619The F<json_xs> command line utility for quick experiments.
1475 1620
1478 Marc Lehmann <schmorp@schmorp.de> 1623 Marc Lehmann <schmorp@schmorp.de>
1479 http://home.schmorp.de/ 1624 http://home.schmorp.de/
1480 1625
1481=cut 1626=cut
1482 1627
16281
1629

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