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Revision 1.140 by root, Thu Jun 27 11:45:17 2013 UTC vs.
Revision 1.170 by root, Thu Nov 15 22:35:35 2018 UTC

35 35
36This module converts Perl data structures to JSON and vice versa. Its 36This module converts Perl data structures to JSON and vice versa. Its
37primary goal is to be I<correct> and its secondary goal is to be 37primary goal is to be I<correct> and its secondary goal is to be
38I<fast>. To reach the latter goal it was written in C. 38I<fast>. To reach the latter goal it was written in C.
39 39
40Beginning with version 2.0 of the JSON module, when both JSON and
41JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
42overridden) with no overhead due to emulation (by inheriting constructor
43and methods). If JSON::XS is not available, it will fall back to the
44compatible JSON::PP module as backend, so using JSON instead of JSON::XS
45gives you a portable JSON API that can be fast when you need and doesn't
46require a C compiler when that is a problem.
47
48As this is the n-th-something JSON module on CPAN, what was the reason
49to write yet another JSON module? While it seems there are many JSON
50modules, none of them correctly handle all corner cases, and in most cases
51their maintainers are unresponsive, gone missing, or not listening to bug
52reports for other reasons.
53
54See MAPPING, below, on how JSON::XS maps perl values to JSON values and 40See MAPPING, below, on how JSON::XS maps perl values to JSON values and
55vice versa. 41vice versa.
56 42
57=head2 FEATURES 43=head2 FEATURES
58 44
59=over 4 45=over
60 46
61=item * correct Unicode handling 47=item * correct Unicode handling
62 48
63This module knows how to handle Unicode, documents how and when it does 49This module knows how to handle Unicode, documents how and when it does
64so, and even documents what "correct" means. 50so, and even documents what "correct" means.
101 87
102package JSON::XS; 88package JSON::XS;
103 89
104use common::sense; 90use common::sense;
105 91
106our $VERSION = 2.34; 92our $VERSION = '4.0';
107our @ISA = qw(Exporter); 93our @ISA = qw(Exporter);
108 94
109our @EXPORT = qw(encode_json decode_json to_json from_json); 95our @EXPORT = qw(encode_json decode_json);
110
111sub to_json($) {
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 96
121use Exporter; 97use Exporter;
122use XSLoader; 98use XSLoader;
123 99
100use Types::Serialiser ();
101
124=head1 FUNCTIONAL INTERFACE 102=head1 FUNCTIONAL INTERFACE
125 103
126The following convenience methods are provided by this module. They are 104The following convenience methods are provided by this module. They are
127exported by default: 105exported by default:
128 106
129=over 4 107=over
130 108
131=item $json_text = encode_json $perl_scalar 109=item $json_text = encode_json $perl_scalar
132 110
133Converts the given Perl data structure to a UTF-8 encoded, binary string 111Converts the given Perl data structure to a UTF-8 encoded, binary string
134(that is, the string contains octets only). Croaks on error. 112(that is, the string contains octets only). Croaks on error.
139 117
140Except being faster. 118Except being faster.
141 119
142=item $perl_scalar = decode_json $json_text 120=item $perl_scalar = decode_json $json_text
143 121
144The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries 122The opposite of C<encode_json>: expects a UTF-8 (binary) string and tries
145to parse that as an UTF-8 encoded JSON text, returning the resulting 123to parse that as a UTF-8 encoded JSON text, returning the resulting
146reference. Croaks on error. 124reference. Croaks on error.
147 125
148This function call is functionally identical to: 126This function call is functionally identical to:
149 127
150 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 128 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
151 129
152Except being faster. 130Except 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.
162 131
163=back 132=back
164 133
165 134
166=head1 A FEW NOTES ON UNICODE AND PERL 135=head1 A FEW NOTES ON UNICODE AND PERL
167 136
168Since this often leads to confusion, here are a few very clear words on 137Since this often leads to confusion, here are a few very clear words on
169how Unicode works in Perl, modulo bugs. 138how Unicode works in Perl, modulo bugs.
170 139
171=over 4 140=over
172 141
173=item 1. Perl strings can store characters with ordinal values > 255. 142=item 1. Perl strings can store characters with ordinal values > 255.
174 143
175This enables you to store Unicode characters as single characters in a 144This enables you to store Unicode characters as single characters in a
176Perl string - very natural. 145Perl string - very natural.
214=head1 OBJECT-ORIENTED INTERFACE 183=head1 OBJECT-ORIENTED INTERFACE
215 184
216The object oriented interface lets you configure your own encoding or 185The object oriented interface lets you configure your own encoding or
217decoding style, within the limits of supported formats. 186decoding style, within the limits of supported formats.
218 187
219=over 4 188=over
220 189
221=item $json = new JSON::XS 190=item $json = new JSON::XS
222 191
223Creates a new JSON::XS object that can be used to de/encode JSON 192Creates a new JSON::XS object that can be used to de/encode JSON
224strings. All boolean flags described below are by default I<disabled>. 193strings. All boolean flags described below are by default I<disabled>
194(with the exception of C<allow_nonref>, which defaults to I<enabled> since
195version C<4.0>).
225 196
226The mutators for flags all return the JSON object again and thus calls can 197The mutators for flags all return the JSON object again and thus calls can
227be chained: 198be chained:
228 199
229 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) 200 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
287 258
288=item $enabled = $json->get_utf8 259=item $enabled = $json->get_utf8
289 260
290If C<$enable> is true (or missing), then the C<encode> method will encode 261If C<$enable> is true (or missing), then the C<encode> method will encode
291the JSON result into UTF-8, as required by many protocols, while the 262the JSON result into UTF-8, as required by many protocols, while the
292C<decode> method expects to be handled an UTF-8-encoded string. Please 263C<decode> method expects to be handed a UTF-8-encoded string. Please
293note that UTF-8-encoded strings do not contain any characters outside the 264note that UTF-8-encoded strings do not contain any characters outside the
294range C<0..255>, they are thus useful for bytewise/binary I/O. In future 265range C<0..255>, they are thus useful for bytewise/binary I/O. In future
295versions, enabling this option might enable autodetection of the UTF-16 266versions, enabling this option might enable autodetection of the UTF-16
296and UTF-32 encoding families, as described in RFC4627. 267and UTF-32 encoding families, as described in RFC4627.
297 268
382 353
383=item $enabled = $json->get_relaxed 354=item $enabled = $json->get_relaxed
384 355
385If C<$enable> is true (or missing), then C<decode> will accept some 356If C<$enable> is true (or missing), then C<decode> will accept some
386extensions to normal JSON syntax (see below). C<encode> will not be 357extensions to normal JSON syntax (see below). C<encode> will not be
387affected in anyway. I<Be aware that this option makes you accept invalid 358affected in any way. I<Be aware that this option makes you accept invalid
388JSON texts as if they were valid!>. I suggest only to use this option to 359JSON texts as if they were valid!>. I suggest only to use this option to
389parse application-specific files written by humans (configuration files, 360parse application-specific files written by humans (configuration files,
390resource files etc.) 361resource files etc.)
391 362
392If C<$enable> is false (the default), then C<decode> will only accept 363If C<$enable> is false (the default), then C<decode> will only accept
393valid JSON texts. 364valid JSON texts.
394 365
395Currently accepted extensions are: 366Currently accepted extensions are:
396 367
397=over 4 368=over
398 369
399=item * list items can have an end-comma 370=item * list items can have an end-comma
400 371
401JSON I<separates> array elements and key-value pairs with commas. This 372JSON I<separates> array elements and key-value pairs with commas. This
402can be annoying if you write JSON texts manually and want to be able to 373can be annoying if you write JSON texts manually and want to be able to
421 [ 392 [
422 1, # this comment not allowed in JSON 393 1, # this comment not allowed in JSON
423 # neither this one... 394 # neither this one...
424 ] 395 ]
425 396
397=item * literal ASCII TAB characters in strings
398
399Literal ASCII TAB characters are now allowed in strings (and treated as
400C<\t>).
401
402 [
403 "Hello\tWorld",
404 "Hello<TAB>World", # literal <TAB> would not normally be allowed
405 ]
406
426=back 407=back
427 408
428=item $json = $json->canonical ([$enable]) 409=item $json = $json->canonical ([$enable])
429 410
430=item $enabled = $json->get_canonical 411=item $enabled = $json->get_canonical
448 429
449=item $json = $json->allow_nonref ([$enable]) 430=item $json = $json->allow_nonref ([$enable])
450 431
451=item $enabled = $json->get_allow_nonref 432=item $enabled = $json->get_allow_nonref
452 433
434Unlike other boolean options, this opotion is enabled by default beginning
435with version C<4.0>. See L<SECURITY CONSIDERATIONS> for the gory details.
436
453If C<$enable> is true (or missing), then the C<encode> method can convert a 437If C<$enable> is true (or missing), then the C<encode> method can convert a
454non-reference into its corresponding string, number or null JSON value, 438non-reference into its corresponding string, number or null JSON value,
455which is an extension to RFC4627. Likewise, C<decode> will accept those JSON 439which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
456values instead of croaking. 440values instead of croaking.
457 441
458If C<$enable> is false, then the C<encode> method will croak if it isn't 442If C<$enable> is false, then the C<encode> method will croak if it isn't
459passed an arrayref or hashref, as JSON texts must either be an object 443passed an arrayref or hashref, as JSON texts must either be an object
460or array. Likewise, C<decode> will croak if given something that is not a 444or array. Likewise, C<decode> will croak if given something that is not a
461JSON object or array. 445JSON object or array.
462 446
463Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>, 447Example, encode a Perl scalar as JSON value without enabled C<allow_nonref>,
464resulting in an invalid JSON text: 448resulting in an error:
465 449
466 JSON::XS->new->allow_nonref->encode ("Hello, World!") 450 JSON::XS->new->allow_nonref (0)->encode ("Hello, World!")
467 => "Hello, World!" 451 => hash- or arrayref expected...
468 452
469=item $json = $json->allow_unknown ([$enable]) 453=item $json = $json->allow_unknown ([$enable])
470 454
471=item $enabled = $json->get_allow_unknown 455=item $enabled = $json->get_allow_unknown
472 456
484 468
485=item $json = $json->allow_blessed ([$enable]) 469=item $json = $json->allow_blessed ([$enable])
486 470
487=item $enabled = $json->get_allow_blessed 471=item $enabled = $json->get_allow_blessed
488 472
473See L<OBJECT SERIALISATION> for details.
474
489If C<$enable> is true (or missing), then the C<encode> method will not 475If C<$enable> is true (or missing), then the C<encode> method will not
490barf when it encounters a blessed reference. Instead, the value of the 476barf when it encounters a blessed reference that it cannot convert
491B<convert_blessed> option will decide whether C<null> (C<convert_blessed> 477otherwise. Instead, a JSON C<null> value is encoded instead of the object.
492disabled or no C<TO_JSON> method found) or a representation of the
493object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
494encoded. Has no effect on C<decode>.
495 478
496If C<$enable> is false (the default), then C<encode> will throw an 479If C<$enable> is false (the default), then C<encode> will throw an
497exception when it encounters a blessed object. 480exception when it encounters a blessed object that it cannot convert
481otherwise.
482
483This setting has no effect on C<decode>.
498 484
499=item $json = $json->convert_blessed ([$enable]) 485=item $json = $json->convert_blessed ([$enable])
500 486
501=item $enabled = $json->get_convert_blessed 487=item $enabled = $json->get_convert_blessed
488
489See L<OBJECT SERIALISATION> for details.
502 490
503If C<$enable> is true (or missing), then C<encode>, upon encountering a 491If C<$enable> is true (or missing), then C<encode>, upon encountering a
504blessed object, will check for the availability of the C<TO_JSON> method 492blessed object, will check for the availability of the C<TO_JSON> method
505on the object's class. If found, it will be called in scalar context 493on the object's class. If found, it will be called in scalar context and
506and the resulting scalar will be encoded instead of the object. If no 494the resulting scalar will be encoded instead of the object.
507C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
508to do.
509 495
510The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON> 496The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
511returns other blessed objects, those will be handled in the same 497returns other blessed objects, those will be handled in the same
512way. C<TO_JSON> must take care of not causing an endless recursion cycle 498way. C<TO_JSON> must take care of not causing an endless recursion cycle
513(== crash) in this case. The name of C<TO_JSON> was chosen because other 499(== crash) in this case. The name of C<TO_JSON> was chosen because other
514methods called by the Perl core (== not by the user of the object) are 500methods called by the Perl core (== not by the user of the object) are
515usually in upper case letters and to avoid collisions with any C<to_json> 501usually in upper case letters and to avoid collisions with any C<to_json>
516function or method. 502function or method.
517 503
518This setting does not yet influence C<decode> in any way, but in the 504If C<$enable> is false (the default), then C<encode> will not consider
519future, global hooks might get installed that influence C<decode> and are 505this type of conversion.
520enabled by this setting.
521 506
522If C<$enable> is false, then the C<allow_blessed> setting will decide what 507This setting has no effect on C<decode>.
523to do when a blessed object is found. 508
509=item $json = $json->allow_tags ([$enable])
510
511=item $enabled = $json->get_allow_tags
512
513See L<OBJECT SERIALISATION> for details.
514
515If C<$enable> is true (or missing), then C<encode>, upon encountering a
516blessed object, will check for the availability of the C<FREEZE> method on
517the object's class. If found, it will be used to serialise the object into
518a nonstandard tagged JSON value (that JSON decoders cannot decode).
519
520It also causes C<decode> to parse such tagged JSON values and deserialise
521them via a call to the C<THAW> method.
522
523If C<$enable> is false (the default), then C<encode> will not consider
524this type of conversion, and tagged JSON values will cause a parse error
525in C<decode>, as if tags were not part of the grammar.
524 526
525=item $json = $json->filter_json_object ([$coderef->($hashref)]) 527=item $json = $json->filter_json_object ([$coderef->($hashref)])
526 528
527When C<$coderef> is specified, it will be called from C<decode> each 529When C<$coderef> is specified, it will be called from C<decode> each
528time it decodes a JSON object. The only argument is a reference to the 530time it decodes a JSON object. The only argument is a reference to
529newly-created hash. If the code references returns a single scalar (which 531the newly-created hash. If the code reference returns a single scalar
530need not be a reference), this value (i.e. a copy of that scalar to avoid 532(which need not be a reference), this value (or rather a copy of it) is
531aliasing) is inserted into the deserialised data structure. If it returns 533inserted into the deserialised data structure. If it returns an empty
532an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the 534list (NOTE: I<not> C<undef>, which is a valid scalar), the original
533original deserialised hash will be inserted. This setting can slow down 535deserialised hash will be inserted. This setting can slow down decoding
534decoding considerably. 536considerably.
535 537
536When C<$coderef> is omitted or undefined, any existing callback will 538When C<$coderef> is omitted or undefined, any existing callback will
537be removed and C<decode> will not change the deserialised hash in any 539be removed and C<decode> will not change the deserialised hash in any
538way. 540way.
539 541
667 669
668See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 670See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
669 671
670=item $json_text = $json->encode ($perl_scalar) 672=item $json_text = $json->encode ($perl_scalar)
671 673
672Converts the given Perl data structure (a simple scalar or a reference 674Converts the given Perl value or data structure to its JSON
673to a hash or array) to its JSON representation. Simple scalars will be 675representation. Croaks on error.
674converted into JSON string or number sequences, while references to arrays
675become JSON arrays and references to hashes become JSON objects. Undefined
676Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
677nor C<false> values will be generated.
678 676
679=item $perl_scalar = $json->decode ($json_text) 677=item $perl_scalar = $json->decode ($json_text)
680 678
681The opposite of C<encode>: expects a JSON text and tries to parse it, 679The opposite of C<encode>: expects a JSON text and tries to parse it,
682returning the resulting simple scalar or reference. Croaks on error. 680returning the resulting simple scalar or reference. Croaks on error.
683
684JSON numbers and strings become simple Perl scalars. JSON arrays become
685Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
686C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
687 681
688=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text) 682=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
689 683
690This works like the C<decode> method, but instead of raising an exception 684This works like the C<decode> method, but instead of raising an exception
691when there is trailing garbage after the first JSON object, it will 685when there is trailing garbage after the first JSON object, it will
692silently stop parsing there and return the number of characters consumed 686silently stop parsing there and return the number of characters consumed
693so far. 687so far.
694 688
695This is useful if your JSON texts are not delimited by an outer protocol 689This is useful if your JSON texts are not delimited by an outer protocol
696(which is not the brightest thing to do in the first place) and you need
697to know where the JSON text ends. 690and you need to know where the JSON text ends.
698 691
699 JSON::XS->new->decode_prefix ("[1] the tail") 692 JSON::XS->new->decode_prefix ("[1] the tail")
700 => ([], 3) 693 => ([1], 3)
701 694
702=back 695=back
703 696
704 697
705=head1 INCREMENTAL PARSING 698=head1 INCREMENTAL PARSING
722to set resource limits (e.g. C<max_size>) to ensure the parser will stop 715to set resource limits (e.g. C<max_size>) to ensure the parser will stop
723parsing in the presence if syntax errors. 716parsing in the presence if syntax errors.
724 717
725The following methods implement this incremental parser. 718The following methods implement this incremental parser.
726 719
727=over 4 720=over
728 721
729=item [void, scalar or list context] = $json->incr_parse ([$string]) 722=item [void, scalar or list context] = $json->incr_parse ([$string])
730 723
731This is the central parsing function. It can both append new text and 724This is the central parsing function. It can both append new text and
732extract objects from the stream accumulated so far (both of these 725extract objects from the stream accumulated so far (both of these
746C<incr_skip> to skip the erroneous part). This is the most common way of 739C<incr_skip> to skip the erroneous part). This is the most common way of
747using the method. 740using the method.
748 741
749And finally, in list context, it will try to extract as many objects 742And finally, in list context, it will try to extract as many objects
750from the stream as it can find and return them, or the empty list 743from the stream as it can find and return them, or the empty list
751otherwise. For this to work, there must be no separators between the JSON 744otherwise. For this to work, there must be no separators (other than
752objects or arrays, instead they must be concatenated back-to-back. If 745whitespace) between the JSON objects or arrays, instead they must be
753an error occurs, an exception will be raised as in the scalar context 746concatenated back-to-back. If an error occurs, an exception will be
754case. Note that in this case, any previously-parsed JSON texts will be 747raised as in the scalar context case. Note that in this case, any
755lost. 748previously-parsed JSON texts will be lost.
756 749
757Example: Parse some JSON arrays/objects in a given string and return 750Example: Parse some JSON arrays/objects in a given string and return
758them. 751them.
759 752
760 my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]"); 753 my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
767all other circumstances you must not call this function (I mean it. 760all other circumstances you must not call this function (I mean it.
768although in simple tests it might actually work, it I<will> fail under 761although in simple tests it might actually work, it I<will> fail under
769real world conditions). As a special exception, you can also call this 762real world conditions). As a special exception, you can also call this
770method before having parsed anything. 763method before having parsed anything.
771 764
765That means you can only use this function to look at or manipulate text
766before or after complete JSON objects, not while the parser is in the
767middle of parsing a JSON object.
768
772This function is useful in two cases: a) finding the trailing text after a 769This function is useful in two cases: a) finding the trailing text after a
773JSON object or b) parsing multiple JSON objects separated by non-JSON text 770JSON object or b) parsing multiple JSON objects separated by non-JSON text
774(such as commas). 771(such as commas).
775 772
776=item $json->incr_skip 773=item $json->incr_skip
795 792
796=back 793=back
797 794
798=head2 LIMITATIONS 795=head2 LIMITATIONS
799 796
800All options that affect decoding are supported, except 797The incremental parser is a non-exact parser: it works by gathering as
801C<allow_nonref>. The reason for this is that it cannot be made to 798much text as possible that I<could> be a valid JSON text, followed by
802work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate 799trying to decode it.
803them back to back and still decode them perfectly. This does not hold true
804for JSON numbers, however.
805 800
806For example, is the string C<1> a single JSON number, or is it simply the 801That means it sometimes needs to read more data than strictly necessary to
807start of C<12>? Or is C<12> a single JSON number, or the concatenation 802diagnose an invalid JSON text. For example, after parsing the following
808of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS 803fragment, the parser I<could> stop with an error, as this fragment
809takes the conservative route and disallows this case. 804I<cannot> be the beginning of a valid JSON text:
805
806 [,
807
808In reality, hopwever, the parser might continue to read data until a
809length limit is exceeded or it finds a closing bracket.
810 810
811=head2 EXAMPLES 811=head2 EXAMPLES
812 812
813Some examples will make all this clearer. First, a simple example that 813Some examples will make all this clearer. First, a simple example that
814works similarly to C<decode_prefix>: We want to decode the JSON object at 814works similarly to C<decode_prefix>: We want to decode the JSON object at
958refers to the abstract Perl language itself. 958refers to the abstract Perl language itself.
959 959
960 960
961=head2 JSON -> PERL 961=head2 JSON -> PERL
962 962
963=over 4 963=over
964 964
965=item object 965=item object
966 966
967A JSON object becomes a reference to a hash in Perl. No ordering of object 967A JSON object becomes a reference to a hash in Perl. No ordering of object
968keys is preserved (JSON does not preserve object key ordering itself). 968keys is preserved (JSON does not preserve object key ordering itself).
1002floating point, JSON::XS only guarantees precision up to but not including 1002floating point, JSON::XS only guarantees precision up to but not including
1003the least significant bit. 1003the least significant bit.
1004 1004
1005=item true, false 1005=item true, false
1006 1006
1007These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, 1007These JSON atoms become C<Types::Serialiser::true> and
1008respectively. They are overloaded to act almost exactly like the numbers 1008C<Types::Serialiser::false>, respectively. They are overloaded to act
1009C<1> and C<0>. You can check whether a scalar is a JSON boolean by using 1009almost exactly like the numbers C<1> and C<0>. You can check whether
1010the C<JSON::XS::is_bool> function. 1010a scalar is a JSON boolean by using the C<Types::Serialiser::is_bool>
1011function (after C<use Types::Serialier>, of course).
1011 1012
1012=item null 1013=item null
1013 1014
1014A JSON null atom becomes C<undef> in Perl. 1015A JSON null atom becomes C<undef> in Perl.
1016
1017=item shell-style comments (C<< # I<text> >>)
1018
1019As a nonstandard extension to the JSON syntax that is enabled by the
1020C<relaxed> setting, shell-style comments are allowed. They can start
1021anywhere outside strings and go till the end of the line.
1022
1023=item tagged values (C<< (I<tag>)I<value> >>).
1024
1025Another nonstandard extension to the JSON syntax, enabled with the
1026C<allow_tags> setting, are tagged values. In this implementation, the
1027I<tag> must be a perl package/class name encoded as a JSON string, and the
1028I<value> must be a JSON array encoding optional constructor arguments.
1029
1030See L<OBJECT SERIALISATION>, below, for details.
1015 1031
1016=back 1032=back
1017 1033
1018 1034
1019=head2 PERL -> JSON 1035=head2 PERL -> JSON
1020 1036
1021The mapping from Perl to JSON is slightly more difficult, as Perl is a 1037The mapping from Perl to JSON is slightly more difficult, as Perl is a
1022truly typeless language, so we can only guess which JSON type is meant by 1038truly typeless language, so we can only guess which JSON type is meant by
1023a Perl value. 1039a Perl value.
1024 1040
1025=over 4 1041=over
1026 1042
1027=item hash references 1043=item hash references
1028 1044
1029Perl hash references become JSON objects. As there is no inherent ordering 1045Perl hash references become JSON objects. As there is no inherent
1030in hash keys (or JSON objects), they will usually be encoded in a 1046ordering in hash keys (or JSON objects), they will usually be encoded
1031pseudo-random order that can change between runs of the same program but 1047in a pseudo-random order. JSON::XS can optionally sort the hash keys
1032stays generally the same within a single run of a program. JSON::XS can 1048(determined by the I<canonical> flag), so the same datastructure will
1033optionally sort the hash keys (determined by the I<canonical> flag), so 1049serialise to the same JSON text (given same settings and version of
1034the same datastructure will serialise to the same JSON text (given same 1050JSON::XS), but this incurs a runtime overhead and is only rarely useful,
1035settings and version of JSON::XS), but this incurs a runtime overhead 1051e.g. when you want to compare some JSON text against another for equality.
1036and is only rarely useful, e.g. when you want to compare some JSON text
1037against another for equality.
1038 1052
1039=item array references 1053=item array references
1040 1054
1041Perl array references become JSON arrays. 1055Perl array references become JSON arrays.
1042 1056
1043=item other references 1057=item other references
1044 1058
1045Other unblessed references are generally not allowed and will cause an 1059Other unblessed references are generally not allowed and will cause an
1046exception to be thrown, except for references to the integers C<0> and 1060exception to be thrown, except for references to the integers C<0> and
1047C<1>, which get turned into C<false> and C<true> atoms in JSON. You can 1061C<1>, which get turned into C<false> and C<true> atoms in JSON.
1048also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
1049 1062
1063Since C<JSON::XS> uses the boolean model from L<Types::Serialiser>, you
1064can also C<use Types::Serialiser> and then use C<Types::Serialiser::false>
1065and C<Types::Serialiser::true> to improve readability.
1066
1067 use Types::Serialiser;
1050 encode_json [\0, JSON::XS::true] # yields [false,true] 1068 encode_json [\0, Types::Serialiser::true] # yields [false,true]
1051 1069
1052=item JSON::XS::true, JSON::XS::false 1070=item Types::Serialiser::true, Types::Serialiser::false
1053 1071
1054These special values become JSON true and JSON false values, 1072These special values from the L<Types::Serialiser> module become JSON true
1055respectively. You can also use C<\1> and C<\0> directly if you want. 1073and JSON false values, respectively. You can also use C<\1> and C<\0>
1074directly if you want.
1056 1075
1057=item blessed objects 1076=item blessed objects
1058 1077
1059Blessed objects are not directly representable in JSON. See the 1078Blessed objects are not directly representable in JSON, but C<JSON::XS>
1060C<allow_blessed> and C<convert_blessed> methods on various options on 1079allows various ways of handling objects. See L<OBJECT SERIALISATION>,
1061how to deal with this: basically, you can choose between throwing an 1080below, for details.
1062exception, encoding the reference as if it weren't blessed, or provide
1063your own serialiser method.
1064 1081
1065=item simple scalars 1082=item simple scalars
1066 1083
1067Simple Perl scalars (any scalar that is not a reference) are the most 1084Simple Perl scalars (any scalar that is not a reference) are the most
1068difficult objects to encode: JSON::XS will encode undefined scalars as 1085difficult objects to encode: JSON::XS will encode undefined scalars as
1105infinities or NaN's - these cannot be represented in JSON, and it is an 1122infinities or NaN's - these cannot be represented in JSON, and it is an
1106error to pass those in. 1123error to pass those in.
1107 1124
1108=back 1125=back
1109 1126
1127=head2 OBJECT SERIALISATION
1128
1129As JSON cannot directly represent Perl objects, you have to choose between
1130a pure JSON representation (without the ability to deserialise the object
1131automatically again), and a nonstandard extension to the JSON syntax,
1132tagged values.
1133
1134=head3 SERIALISATION
1135
1136What happens when C<JSON::XS> encounters a Perl object depends on the
1137C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are
1138used in this order:
1139
1140=over
1141
1142=item 1. C<allow_tags> is enabled and the object has a C<FREEZE> method.
1143
1144In this case, C<JSON::XS> uses the L<Types::Serialiser> object
1145serialisation protocol to create a tagged JSON value, using a nonstandard
1146extension to the JSON syntax.
1147
1148This works by invoking the C<FREEZE> method on the object, with the first
1149argument being the object to serialise, and the second argument being the
1150constant string C<JSON> to distinguish it from other serialisers.
1151
1152The C<FREEZE> method can return any number of values (i.e. zero or
1153more). These values and the paclkage/classname of the object will then be
1154encoded as a tagged JSON value in the following format:
1155
1156 ("classname")[FREEZE return values...]
1157
1158e.g.:
1159
1160 ("URI")["http://www.google.com/"]
1161 ("MyDate")[2013,10,29]
1162 ("ImageData::JPEG")["Z3...VlCg=="]
1163
1164For example, the hypothetical C<My::Object> C<FREEZE> method might use the
1165objects C<type> and C<id> members to encode the object:
1166
1167 sub My::Object::FREEZE {
1168 my ($self, $serialiser) = @_;
1169
1170 ($self->{type}, $self->{id})
1171 }
1172
1173=item 2. C<convert_blessed> is enabled and the object has a C<TO_JSON> method.
1174
1175In this case, the C<TO_JSON> method of the object is invoked in scalar
1176context. It must return a single scalar that can be directly encoded into
1177JSON. This scalar replaces the object in the JSON text.
1178
1179For example, the following C<TO_JSON> method will convert all L<URI>
1180objects to JSON strings when serialised. The fatc that these values
1181originally were L<URI> objects is lost.
1182
1183 sub URI::TO_JSON {
1184 my ($uri) = @_;
1185 $uri->as_string
1186 }
1187
1188=item 3. C<allow_blessed> is enabled.
1189
1190The object will be serialised as a JSON null value.
1191
1192=item 4. none of the above
1193
1194If none of the settings are enabled or the respective methods are missing,
1195C<JSON::XS> throws an exception.
1196
1197=back
1198
1199=head3 DESERIALISATION
1200
1201For deserialisation there are only two cases to consider: either
1202nonstandard tagging was used, in which case C<allow_tags> decides,
1203or objects cannot be automatically be deserialised, in which
1204case you can use postprocessing or the C<filter_json_object> or
1205C<filter_json_single_key_object> callbacks to get some real objects our of
1206your JSON.
1207
1208This section only considers the tagged value case: I a tagged JSON object
1209is encountered during decoding and C<allow_tags> is disabled, a parse
1210error will result (as if tagged values were not part of the grammar).
1211
1212If C<allow_tags> is enabled, C<JSON::XS> will look up the C<THAW> method
1213of the package/classname used during serialisation (it will not attempt
1214to load the package as a Perl module). If there is no such method, the
1215decoding will fail with an error.
1216
1217Otherwise, the C<THAW> method is invoked with the classname as first
1218argument, the constant string C<JSON> as second argument, and all the
1219values from the JSON array (the values originally returned by the
1220C<FREEZE> method) as remaining arguments.
1221
1222The method must then return the object. While technically you can return
1223any Perl scalar, you might have to enable the C<enable_nonref> setting to
1224make that work in all cases, so better return an actual blessed reference.
1225
1226As an example, let's implement a C<THAW> function that regenerates the
1227C<My::Object> from the C<FREEZE> example earlier:
1228
1229 sub My::Object::THAW {
1230 my ($class, $serialiser, $type, $id) = @_;
1231
1232 $class->new (type => $type, id => $id)
1233 }
1234
1110 1235
1111=head1 ENCODING/CODESET FLAG NOTES 1236=head1 ENCODING/CODESET FLAG NOTES
1112 1237
1113The interested reader might have seen a number of flags that signify 1238The interested reader might have seen a number of flags that signify
1114encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be 1239encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
1131takes those codepoint numbers and I<encodes> them, in our case into 1256takes those codepoint numbers and I<encodes> them, in our case into
1132octets. Unicode is (among other things) a codeset, UTF-8 is an encoding, 1257octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
1133and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at 1258and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
1134the same time, which can be confusing. 1259the same time, which can be confusing.
1135 1260
1136=over 4 1261=over
1137 1262
1138=item C<utf8> flag disabled 1263=item C<utf8> flag disabled
1139 1264
1140When C<utf8> is disabled (the default), then C<encode>/C<decode> generate 1265When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
1141and expect Unicode strings, that is, characters with high ordinal Unicode 1266and expect Unicode strings, that is, characters with high ordinal Unicode
1158expect your input strings to be encoded as UTF-8, that is, no "character" 1283expect your input strings to be encoded as UTF-8, that is, no "character"
1159of the input string must have any value > 255, as UTF-8 does not allow 1284of the input string must have any value > 255, as UTF-8 does not allow
1160that. 1285that.
1161 1286
1162The C<utf8> flag therefore switches between two modes: disabled means you 1287The C<utf8> flag therefore switches between two modes: disabled means you
1163will get a Unicode string in Perl, enabled means you get an UTF-8 encoded 1288will get a Unicode string in Perl, enabled means you get a UTF-8 encoded
1164octet/binary string in Perl. 1289octet/binary string in Perl.
1165 1290
1166=item C<latin1> or C<ascii> flags enabled 1291=item C<latin1> or C<ascii> flags enabled
1167 1292
1168With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters 1293With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
1300general you should not try to generate YAML with a JSON generator or vice 1425general you should not try to generate YAML with a JSON generator or vice
1301versa, or try to parse JSON with a YAML parser or vice versa: chances are 1426versa, or try to parse JSON with a YAML parser or vice versa: chances are
1302high that you will run into severe interoperability problems when you 1427high that you will run into severe interoperability problems when you
1303least expect it. 1428least expect it.
1304 1429
1305=over 4 1430=over
1306 1431
1307=item (*) 1432=item (*)
1308 1433
1309I have been pressured multiple times by Brian Ingerson (one of the 1434I have been pressured multiple times by Brian Ingerson (one of the
1310authors of the YAML specification) to remove this paragraph, despite him 1435authors of the YAML specification) to remove this paragraph, despite him
1436are browser design bugs, but it is still you who will have to deal with 1561are browser design bugs, but it is still you who will have to deal with
1437it, as major browser developers care only for features, not about getting 1562it, as major browser developers care only for features, not about getting
1438security right). 1563security right).
1439 1564
1440 1565
1566=head2 "OLD" VS. "NEW" JSON (RFC4627 VS. RFC7159)
1567
1568JSON originally required JSON texts to represent an array or object -
1569scalar values were explicitly not allowed. This has changed, and versions
1570of JSON::XS beginning with C<4.0> reflect this by allowing scalar values
1571by default.
1572
1573One reason why one might not want this is that this removes a fundamental
1574property of JSON texts, namely that they are self-delimited and
1575self-contained, or in other words, you could take any number of "old"
1576JSON texts and paste them together, and the result would be unambiguously
1577parseable:
1578
1579 [1,3]{"k":5}[][null] # four JSON texts, without doubt
1580
1581By allowing scalars, this property is lost: in the following example, is
1582this one JSON text (the number 12) or two JSON texts (the numbers 1 and
15832):
1584
1585 12 # could be 12, or 1 and 2
1586
1587Another lost property of "old" JSON is that no lookahead is required to
1588know the end of a JSON text, i.e. the JSON text definitely ended at the
1589last C<]> or C<}> character, there was no need to read extra characters.
1590
1591For example, a viable network protocol with "old" JSON was to simply
1592exchange JSON texts without delimiter. For "new" JSON, you have to use a
1593suitable delimiter (such as a newline) after every JSON text or ensure you
1594never encode/decode scalar values.
1595
1596Most protocols do work by only transferring arrays or objects, and the
1597easiest way to avoid problems with the "new" JSON definition is to
1598explicitly disallow scalar values in your encoder and decoder:
1599
1600 $json_coder = JSON::XS->new->allow_nonref (0)
1601
1602This is a somewhat unhappy situation, and the blame can fully be put on
1603JSON's inmventor, Douglas Crockford, who unilaterally changed the format
1604in 2006 without consulting the IETF, forcing the IETF to either fork the
1605format or go with it (as I was told, the IETF wasn't amused).
1606
1607
1608=head1 RELATIONSHIP WITH I-JSON
1609
1610JSON is a somewhat sloppily-defined format - it carries around obvious
1611Javascript baggage, such as not really defining number range, probably
1612because Javascript only has one type of numbers: IEEE 64 bit floats
1613("binary64").
1614
1615For this reaosn, RFC7493 defines "Internet JSON", which is a restricted
1616subset of JSON that is supposedly more interoperable on the internet.
1617
1618While C<JSON::XS> does not offer specific support for I-JSON, it of course
1619accepts valid I-JSON and by default implements some of the limitations
1620of I-JSON, such as parsing numbers as perl numbers, which are usually a
1621superset of binary64 numbers.
1622
1623To generate I-JSON, follow these rules:
1624
1625=over
1626
1627=item * always generate UTF-8
1628
1629I-JSON must be encoded in UTF-8, the default for C<encode_json>.
1630
1631=item * numbers should be within IEEE 754 binary64 range
1632
1633Basically all existing perl installations use binary64 to represent
1634floating point numbers, so all you need to do is to avoid large integers.
1635
1636=item * objects must not have duplicate keys
1637
1638This is trivially done, as C<JSON::XS> does not allow duplicate keys.
1639
1640=item * do not generate scalar JSON texts, use C<< ->allow_nonref (0) >>
1641
1642I-JSON strongly requests you to only encode arrays and objects into JSON.
1643
1644=item * times should be strings in ISO 8601 format
1645
1646There are a myriad of modules on CPAN dealing with ISO 8601 - search for
1647C<ISO8601> on CPAN and use one.
1648
1649=item * encode binary data as base64
1650
1651While it's tempting to just dump binary data as a string (and let
1652C<JSON::XS> do the escaping), for I-JSON, it's I<recommended> to encode
1653binary data as base64.
1654
1655=back
1656
1657There are some other considerations - read RFC7493 for the details if
1658interested.
1659
1660
1661=head1 INTEROPERABILITY WITH OTHER MODULES
1662
1663C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean
1664constants. That means that the JSON true and false values will be
1665comaptible to true and false values of other modules that do the same,
1666such as L<JSON::PP> and L<CBOR::XS>.
1667
1668
1669=head1 INTEROPERABILITY WITH OTHER JSON DECODERS
1670
1671As long as you only serialise data that can be directly expressed in JSON,
1672C<JSON::XS> is incapable of generating invalid JSON output (modulo bugs,
1673but C<JSON::XS> has found more bugs in the official JSON testsuite (1)
1674than the official JSON testsuite has found in C<JSON::XS> (0)).
1675
1676When you have trouble decoding JSON generated by this module using other
1677decoders, then it is very likely that you have an encoding mismatch or the
1678other decoder is broken.
1679
1680When decoding, C<JSON::XS> is strict by default and will likely catch all
1681errors. There are currently two settings that change this: C<relaxed>
1682makes C<JSON::XS> accept (but not generate) some non-standard extensions,
1683and C<allow_tags> will allow you to encode and decode Perl objects, at the
1684cost of not outputting valid JSON anymore.
1685
1686=head2 TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
1687
1688When you use C<allow_tags> to use the extended (and also nonstandard and
1689invalid) JSON syntax for serialised objects, and you still want to decode
1690the generated When you want to serialise objects, you can run a regex
1691to replace the tagged syntax by standard JSON arrays (it only works for
1692"normal" package names without comma, newlines or single colons). First,
1693the readable Perl version:
1694
1695 # if your FREEZE methods return no values, you need this replace first:
1696 $json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[\s*\]/[$1]/gx;
1697
1698 # this works for non-empty constructor arg lists:
1699 $json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[/[$1,/gx;
1700
1701And here is a less readable version that is easy to adapt to other
1702languages:
1703
1704 $json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/[$1,/g;
1705
1706Here is an ECMAScript version (same regex):
1707
1708 json = json.replace (/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/g, "[$1,");
1709
1710Since this syntax converts to standard JSON arrays, it might be hard to
1711distinguish serialised objects from normal arrays. You can prepend a
1712"magic number" as first array element to reduce chances of a collision:
1713
1714 $json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;
1715
1716And after decoding the JSON text, you could walk the data
1717structure looking for arrays with a first element of
1718C<XU1peReLzT4ggEllLanBYq4G9VzliwKF>.
1719
1720The same approach can be used to create the tagged format with another
1721encoder. First, you create an array with the magic string as first member,
1722the classname as second, and constructor arguments last, encode it as part
1723of your JSON structure, and then:
1724
1725 $json =~ s/\[\s*"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s*,\s*("([^\\":,]+|\\.|::)*")\s*,/($1)[/g;
1726
1727Again, this has some limitations - the magic string must not be encoded
1728with character escapes, and the constructor arguments must be non-empty.
1729
1730
1441=head1 THREADS 1731=head1 (I-)THREADS
1442 1732
1443This module is I<not> guaranteed to be thread safe and there are no 1733This module is I<not> guaranteed to be ithread (or MULTIPLICITY-) safe
1444plans to change this until Perl gets thread support (as opposed to the 1734and there are no plans to change this. Note that perl's builtin so-called
1445horribly slow so-called "threads" which are simply slow and bloated 1735threads/ithreads are officially deprecated and should not be used.
1446process simulations - use fork, it's I<much> faster, cheaper, better).
1447
1448(It might actually work, but you have been warned).
1449 1736
1450 1737
1451=head1 THE PERILS OF SETLOCALE 1738=head1 THE PERILS OF SETLOCALE
1452 1739
1453Sometimes people avoid the Perl locale support and directly call the 1740Sometimes people avoid the Perl locale support and directly call the
1464If you need C<LC_NUMERIC>, you should enable it only around the code that 1751If you need C<LC_NUMERIC>, you should enable it only around the code that
1465actually needs it (avoiding stringification of numbers), and restore it 1752actually needs it (avoiding stringification of numbers), and restore it
1466afterwards. 1753afterwards.
1467 1754
1468 1755
1756=head1 SOME HISTORY
1757
1758At the time this module was created there already were a number of JSON
1759modules available on CPAN, so what was the reason to write yet another
1760JSON module? While it seems there are many JSON modules, none of them
1761correctly handled all corner cases, and in most cases their maintainers
1762are unresponsive, gone missing, or not listening to bug reports for other
1763reasons.
1764
1765Beginning with version 2.0 of the JSON module, when both JSON and
1766JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
1767overridden) with no overhead due to emulation (by inheriting constructor
1768and methods). If JSON::XS is not available, it will fall back to the
1769compatible JSON::PP module as backend, so using JSON instead of JSON::XS
1770gives you a portable JSON API that can be fast when you need it and
1771doesn't require a C compiler when that is a problem.
1772
1773Somewhere around version 3, this module was forked into
1774C<Cpanel::JSON::XS>, because its maintainer had serious trouble
1775understanding JSON and insisted on a fork with many bugs "fixed" that
1776weren't actually bugs, while spreading FUD about this module without
1777actually giving any details on his accusations. You be the judge, but
1778in my personal opinion, if you want quality, you will stay away from
1779dangerous forks like that.
1780
1781
1469=head1 BUGS 1782=head1 BUGS
1470 1783
1471While the goal of this module is to be correct, that unfortunately does 1784While the goal of this module is to be correct, that unfortunately does
1472not mean it's bug-free, only that I think its design is bug-free. If you 1785not mean it's bug-free, only that I think its design is bug-free. If you
1473keep reporting bugs they will be fixed swiftly, though. 1786keep reporting bugs they will be fixed swiftly, though.
1475Please refrain from using rt.cpan.org or any other bug reporting 1788Please refrain from using rt.cpan.org or any other bug reporting
1476service. I put the contact address into my modules for a reason. 1789service. I put the contact address into my modules for a reason.
1477 1790
1478=cut 1791=cut
1479 1792
1480our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" }; 1793BEGIN {
1481our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" }; 1794 *true = \$Types::Serialiser::true;
1795 *true = \&Types::Serialiser::true;
1796 *false = \$Types::Serialiser::false;
1797 *false = \&Types::Serialiser::false;
1798 *is_bool = \&Types::Serialiser::is_bool;
1482 1799
1483sub true() { $true } 1800 *JSON::XS::Boolean:: = *Types::Serialiser::Boolean::;
1484sub false() { $false }
1485
1486sub is_bool($) {
1487 UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
1488# or UNIVERSAL::isa $_[0], "JSON::Literal"
1489} 1801}
1490 1802
1491XSLoader::load "JSON::XS", $VERSION; 1803XSLoader::load "JSON::XS", $VERSION;
1492
1493package JSON::XS::Boolean;
1494
1495use overload
1496 "0+" => sub { ${$_[0]} },
1497 "++" => sub { $_[0] = ${$_[0]} + 1 },
1498 "--" => sub { $_[0] = ${$_[0]} - 1 },
1499 fallback => 1;
1500
15011;
1502 1804
1503=head1 SEE ALSO 1805=head1 SEE ALSO
1504 1806
1505The F<json_xs> command line utility for quick experiments. 1807The F<json_xs> command line utility for quick experiments.
1506 1808
1509 Marc Lehmann <schmorp@schmorp.de> 1811 Marc Lehmann <schmorp@schmorp.de>
1510 http://home.schmorp.de/ 1812 http://home.schmorp.de/
1511 1813
1512=cut 1814=cut
1513 1815
18161
1817

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