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1 | =encoding utf-8 |
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2 | |
1 | =head1 NAME |
3 | =head1 NAME |
2 | |
4 | |
3 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
5 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
4 | |
6 | |
5 | JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ |
7 | JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ |
… | |
… | |
10 | use JSON::XS; |
12 | use JSON::XS; |
11 | |
13 | |
12 | # exported functions, they croak on error |
14 | # exported functions, they croak on error |
13 | # and expect/generate UTF-8 |
15 | # and expect/generate UTF-8 |
14 | |
16 | |
15 | $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; |
17 | $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref; |
16 | $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; |
18 | $perl_hash_or_arrayref = decode_json $utf8_encoded_json_text; |
17 | |
19 | |
18 | # OO-interface |
20 | # OO-interface |
19 | |
21 | |
20 | $coder = JSON::XS->new->ascii->pretty->allow_nonref; |
22 | $coder = JSON::XS->new->ascii->pretty->allow_nonref; |
21 | $pretty_printed_unencoded = $coder->encode ($perl_scalar); |
23 | $pretty_printed_unencoded = $coder->encode ($perl_scalar); |
22 | $perl_scalar = $coder->decode ($unicode_json_text); |
24 | $perl_scalar = $coder->decode ($unicode_json_text); |
23 | |
25 | |
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26 | # Note that JSON version 2.0 and above will automatically use JSON::XS |
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27 | # if available, at virtually no speed overhead either, so you should |
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28 | # be able to just: |
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29 | |
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30 | use JSON; |
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31 | |
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32 | # and do the same things, except that you have a pure-perl fallback now. |
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33 | |
24 | =head1 DESCRIPTION |
34 | =head1 DESCRIPTION |
25 | |
35 | |
26 | This module converts Perl data structures to JSON and vice versa. Its |
36 | This module converts Perl data structures to JSON and vice versa. Its |
27 | primary goal is to be I<correct> and its secondary goal is to be |
37 | primary goal is to be I<correct> and its secondary goal is to be |
28 | I<fast>. To reach the latter goal it was written in C. |
38 | I<fast>. To reach the latter goal it was written in C. |
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39 | |
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40 | Beginning with version 2.0 of the JSON module, when both JSON and |
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41 | JSON::XS are installed, then JSON will fall back on JSON::XS (this can be |
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42 | overriden) with no overhead due to emulation (by inheritign constructor |
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43 | and methods). If JSON::XS is not available, it will fall back to the |
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44 | compatible JSON::PP module as backend, so using JSON instead of JSON::XS |
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45 | gives you a portable JSON API that can be fast when you need and doesn't |
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46 | require a C compiler when that is a problem. |
29 | |
47 | |
30 | As this is the n-th-something JSON module on CPAN, what was the reason |
48 | As this is the n-th-something JSON module on CPAN, what was the reason |
31 | to write yet another JSON module? While it seems there are many JSON |
49 | to write yet another JSON module? While it seems there are many JSON |
32 | modules, none of them correctly handle all corner cases, and in most cases |
50 | modules, none of them correctly handle all corner cases, and in most cases |
33 | their maintainers are unresponsive, gone missing, or not listening to bug |
51 | their maintainers are unresponsive, gone missing, or not listening to bug |
… | |
… | |
42 | |
60 | |
43 | =over 4 |
61 | =over 4 |
44 | |
62 | |
45 | =item * correct Unicode handling |
63 | =item * correct Unicode handling |
46 | |
64 | |
47 | This module knows how to handle Unicode, and even documents how and when |
65 | This module knows how to handle Unicode, documents how and when it does |
48 | it does so. |
66 | so, and even documents what "correct" means. |
49 | |
67 | |
50 | =item * round-trip integrity |
68 | =item * round-trip integrity |
51 | |
69 | |
52 | When you serialise a perl data structure using only datatypes supported |
70 | When you serialise a perl data structure using only datatypes supported |
53 | by JSON, the deserialised data structure is identical on the Perl level. |
71 | by JSON, the deserialised data structure is identical on the Perl level. |
54 | (e.g. the string "2.0" doesn't suddenly become "2" just because it looks |
72 | (e.g. the string "2.0" doesn't suddenly become "2" just because it looks |
55 | like a number). |
73 | like a number). There minor I<are> exceptions to this, read the MAPPING |
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74 | section below to learn about those. |
56 | |
75 | |
57 | =item * strict checking of JSON correctness |
76 | =item * strict checking of JSON correctness |
58 | |
77 | |
59 | There is no guessing, no generating of illegal JSON texts by default, |
78 | There is no guessing, no generating of illegal JSON texts by default, |
60 | and only JSON is accepted as input by default (the latter is a security |
79 | and only JSON is accepted as input by default (the latter is a security |
61 | feature). |
80 | feature). |
62 | |
81 | |
63 | =item * fast |
82 | =item * fast |
64 | |
83 | |
65 | Compared to other JSON modules, this module compares favourably in terms |
84 | Compared to other JSON modules and other serialisers such as Storable, |
66 | of speed, too. |
85 | this module usually compares favourably in terms of speed, too. |
67 | |
86 | |
68 | =item * simple to use |
87 | =item * simple to use |
69 | |
88 | |
70 | This module has both a simple functional interface as well as an OO |
89 | This module has both a simple functional interface as well as an objetc |
71 | interface. |
90 | oriented interface interface. |
72 | |
91 | |
73 | =item * reasonably versatile output formats |
92 | =item * reasonably versatile output formats |
74 | |
93 | |
75 | You can choose between the most compact guaranteed single-line format |
94 | You can choose between the most compact guaranteed-single-line format |
76 | possible (nice for simple line-based protocols), a pure-ascii format |
95 | possible (nice for simple line-based protocols), a pure-ascii format |
77 | (for when your transport is not 8-bit clean, still supports the whole |
96 | (for when your transport is not 8-bit clean, still supports the whole |
78 | Unicode range), or a pretty-printed format (for when you want to read that |
97 | Unicode range), or a pretty-printed format (for when you want to read that |
79 | stuff). Or you can combine those features in whatever way you like. |
98 | stuff). Or you can combine those features in whatever way you like. |
80 | |
99 | |
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84 | |
103 | |
85 | package JSON::XS; |
104 | package JSON::XS; |
86 | |
105 | |
87 | use strict; |
106 | use strict; |
88 | |
107 | |
89 | our $VERSION = '1.53'; |
108 | our $VERSION = '2.01'; |
90 | our @ISA = qw(Exporter); |
109 | our @ISA = qw(Exporter); |
91 | |
110 | |
92 | our @EXPORT = qw(to_json from_json); |
111 | our @EXPORT = qw(encode_json decode_json to_json from_json); |
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112 | |
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113 | sub to_json($) { |
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114 | require Carp; |
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115 | 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"); |
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116 | } |
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117 | |
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118 | sub from_json($) { |
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119 | require Carp; |
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120 | 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"); |
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121 | } |
93 | |
122 | |
94 | use Exporter; |
123 | use Exporter; |
95 | use XSLoader; |
124 | use XSLoader; |
96 | |
125 | |
97 | =head1 FUNCTIONAL INTERFACE |
126 | =head1 FUNCTIONAL INTERFACE |
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99 | The following convenience methods are provided by this module. They are |
128 | The following convenience methods are provided by this module. They are |
100 | exported by default: |
129 | exported by default: |
101 | |
130 | |
102 | =over 4 |
131 | =over 4 |
103 | |
132 | |
104 | =item $json_text = to_json $perl_scalar |
133 | =item $json_text = encode_json $perl_scalar |
105 | |
134 | |
106 | Converts the given Perl data structure to a UTF-8 encoded, binary string |
135 | Converts the given Perl data structure to a UTF-8 encoded, binary string |
107 | (that is, the string contains octets only). Croaks on error. |
136 | (that is, the string contains octets only). Croaks on error. |
108 | |
137 | |
109 | This function call is functionally identical to: |
138 | This function call is functionally identical to: |
110 | |
139 | |
111 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
140 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
112 | |
141 | |
113 | except being faster. |
142 | except being faster. |
114 | |
143 | |
115 | =item $perl_scalar = from_json $json_text |
144 | =item $perl_scalar = decode_json $json_text |
116 | |
145 | |
117 | The opposite of C<to_json>: expects an UTF-8 (binary) string and tries |
146 | The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries |
118 | to parse that as an UTF-8 encoded JSON text, returning the resulting |
147 | to parse that as an UTF-8 encoded JSON text, returning the resulting |
119 | reference. Croaks on error. |
148 | reference. Croaks on error. |
120 | |
149 | |
121 | This function call is functionally identical to: |
150 | This function call is functionally identical to: |
122 | |
151 | |
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148 | This enables you to store Unicode characters as single characters in a |
177 | This enables you to store Unicode characters as single characters in a |
149 | Perl string - very natural. |
178 | Perl string - very natural. |
150 | |
179 | |
151 | =item 2. Perl does I<not> associate an encoding with your strings. |
180 | =item 2. Perl does I<not> associate an encoding with your strings. |
152 | |
181 | |
153 | Unless you force it to, e.g. when matching it against a regex, or printing |
182 | ... until you force it to, e.g. when matching it against a regex, or |
154 | the scalar to a file, in which case Perl either interprets your string as |
183 | printing the scalar to a file, in which case Perl either interprets your |
155 | locale-encoded text, octets/binary, or as Unicode, depending on various |
184 | string as locale-encoded text, octets/binary, or as Unicode, depending |
156 | settings. In no case is an encoding stored together with your data, it is |
185 | on various settings. In no case is an encoding stored together with your |
157 | I<use> that decides encoding, not any magical metadata. |
186 | data, it is I<use> that decides encoding, not any magical meta data. |
158 | |
187 | |
159 | =item 3. The internal utf-8 flag has no meaning with regards to the |
188 | =item 3. The internal utf-8 flag has no meaning with regards to the |
160 | encoding of your string. |
189 | encoding of your string. |
161 | |
190 | |
162 | Just ignore that flag unless you debug a Perl bug, a module written in |
191 | Just ignore that flag unless you debug a Perl bug, a module written in |
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276 | |
305 | |
277 | use Encode; |
306 | use Encode; |
278 | $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext); |
307 | $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext); |
279 | |
308 | |
280 | =item $json = $json->pretty ([$enable]) |
309 | =item $json = $json->pretty ([$enable]) |
281 | |
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282 | =item $enabled = $json->get_pretty |
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283 | |
310 | |
284 | This enables (or disables) all of the C<indent>, C<space_before> and |
311 | This enables (or disables) all of the C<indent>, C<space_before> and |
285 | C<space_after> (and in the future possibly more) flags in one call to |
312 | C<space_after> (and in the future possibly more) flags in one call to |
286 | generate the most readable (or most compact) form possible. |
313 | generate the most readable (or most compact) form possible. |
287 | |
314 | |
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429 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
456 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
430 | => "Hello, World!" |
457 | => "Hello, World!" |
431 | |
458 | |
432 | =item $json = $json->allow_blessed ([$enable]) |
459 | =item $json = $json->allow_blessed ([$enable]) |
433 | |
460 | |
434 | =item $enabled = $json->get_allow_bless |
461 | =item $enabled = $json->get_allow_blessed |
435 | |
462 | |
436 | If C<$enable> is true (or missing), then the C<encode> method will not |
463 | If C<$enable> is true (or missing), then the C<encode> method will not |
437 | barf when it encounters a blessed reference. Instead, the value of the |
464 | barf when it encounters a blessed reference. Instead, the value of the |
438 | B<convert_blessed> option will decide whether C<null> (C<convert_blessed> |
465 | B<convert_blessed> option will decide whether C<null> (C<convert_blessed> |
439 | disabled or no C<to_json> method found) or a representation of the |
466 | disabled or no C<TO_JSON> method found) or a representation of the |
440 | object (C<convert_blessed> enabled and C<to_json> method found) is being |
467 | object (C<convert_blessed> enabled and C<TO_JSON> method found) is being |
441 | encoded. Has no effect on C<decode>. |
468 | encoded. Has no effect on C<decode>. |
442 | |
469 | |
443 | If C<$enable> is false (the default), then C<encode> will throw an |
470 | If C<$enable> is false (the default), then C<encode> will throw an |
444 | exception when it encounters a blessed object. |
471 | exception when it encounters a blessed object. |
445 | |
472 | |
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457 | The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON> |
484 | The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON> |
458 | returns other blessed objects, those will be handled in the same |
485 | returns other blessed objects, those will be handled in the same |
459 | way. C<TO_JSON> must take care of not causing an endless recursion cycle |
486 | way. C<TO_JSON> must take care of not causing an endless recursion cycle |
460 | (== crash) in this case. The name of C<TO_JSON> was chosen because other |
487 | (== crash) in this case. The name of C<TO_JSON> was chosen because other |
461 | methods called by the Perl core (== not by the user of the object) are |
488 | methods called by the Perl core (== not by the user of the object) are |
462 | usually in upper case letters and to avoid collisions with the C<to_json> |
489 | usually in upper case letters and to avoid collisions with any C<to_json> |
463 | function. |
490 | function or method. |
464 | |
491 | |
465 | This setting does not yet influence C<decode> in any way, but in the |
492 | This setting does not yet influence C<decode> in any way, but in the |
466 | future, global hooks might get installed that influence C<decode> and are |
493 | future, global hooks might get installed that influence C<decode> and are |
467 | enabled by this setting. |
494 | enabled by this setting. |
468 | |
495 | |
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682 | |
709 | |
683 | A JSON number becomes either an integer, numeric (floating point) or |
710 | A JSON number becomes either an integer, numeric (floating point) or |
684 | string scalar in perl, depending on its range and any fractional parts. On |
711 | string scalar in perl, depending on its range and any fractional parts. On |
685 | the Perl level, there is no difference between those as Perl handles all |
712 | the Perl level, there is no difference between those as Perl handles all |
686 | the conversion details, but an integer may take slightly less memory and |
713 | the conversion details, but an integer may take slightly less memory and |
687 | might represent more values exactly than (floating point) numbers. |
714 | might represent more values exactly than floating point numbers. |
688 | |
715 | |
689 | If the number consists of digits only, JSON::XS will try to represent |
716 | If the number consists of digits only, JSON::XS will try to represent |
690 | it as an integer value. If that fails, it will try to represent it as |
717 | it as an integer value. If that fails, it will try to represent it as |
691 | a numeric (floating point) value if that is possible without loss of |
718 | a numeric (floating point) value if that is possible without loss of |
692 | precision. Otherwise it will preserve the number as a string value. |
719 | precision. Otherwise it will preserve the number as a string value (in |
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720 | which case you lose roundtripping ability, as the JSON number will be |
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721 | re-encoded toa JSON string). |
693 | |
722 | |
694 | Numbers containing a fractional or exponential part will always be |
723 | Numbers containing a fractional or exponential part will always be |
695 | represented as numeric (floating point) values, possibly at a loss of |
724 | represented as numeric (floating point) values, possibly at a loss of |
696 | precision. |
725 | precision (in which case you might lose perfect roundtripping ability, but |
697 | |
726 | the JSON number will still be re-encoded as a JSON number). |
698 | This might create round-tripping problems as numbers might become strings, |
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699 | but as Perl is typeless there is no other way to do it. |
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700 | |
727 | |
701 | =item true, false |
728 | =item true, false |
702 | |
729 | |
703 | These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, |
730 | These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, |
704 | respectively. They are overloaded to act almost exactly like the numbers |
731 | respectively. They are overloaded to act almost exactly like the numbers |
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741 | Other unblessed references are generally not allowed and will cause an |
768 | Other unblessed references are generally not allowed and will cause an |
742 | exception to be thrown, except for references to the integers C<0> and |
769 | exception to be thrown, except for references to the integers C<0> and |
743 | C<1>, which get turned into C<false> and C<true> atoms in JSON. You can |
770 | C<1>, which get turned into C<false> and C<true> atoms in JSON. You can |
744 | also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. |
771 | also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. |
745 | |
772 | |
746 | to_json [\0,JSON::XS::true] # yields [false,true] |
773 | encode_json [\0,JSON::XS::true] # yields [false,true] |
747 | |
774 | |
748 | =item JSON::XS::true, JSON::XS::false |
775 | =item JSON::XS::true, JSON::XS::false |
749 | |
776 | |
750 | These special values become JSON true and JSON false values, |
777 | These special values become JSON true and JSON false values, |
751 | respectively. You can also use C<\1> and C<\0> directly if you want. |
778 | respectively. You can also use C<\1> and C<\0> directly if you want. |
752 | |
779 | |
753 | =item blessed objects |
780 | =item blessed objects |
754 | |
781 | |
755 | Blessed objects are not allowed. JSON::XS currently tries to encode their |
782 | Blessed objects are not directly representable in JSON. See the |
756 | underlying representation (hash- or arrayref), but this behaviour might |
783 | C<allow_blessed> and C<convert_blessed> methods on various options on |
757 | change in future versions. |
784 | how to deal with this: basically, you can choose between throwing an |
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785 | exception, encoding the reference as if it weren't blessed, or provide |
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786 | your own serialiser method. |
758 | |
787 | |
759 | =item simple scalars |
788 | =item simple scalars |
760 | |
789 | |
761 | Simple Perl scalars (any scalar that is not a reference) are the most |
790 | Simple Perl scalars (any scalar that is not a reference) are the most |
762 | difficult objects to encode: JSON::XS will encode undefined scalars as |
791 | difficult objects to encode: JSON::XS will encode undefined scalars as |
763 | JSON null value, scalars that have last been used in a string context |
792 | JSON C<null> values, scalars that have last been used in a string context |
764 | before encoding as JSON strings and anything else as number value: |
793 | before encoding as JSON strings, and anything else as number value: |
765 | |
794 | |
766 | # dump as number |
795 | # dump as number |
767 | to_json [2] # yields [2] |
796 | encode_json [2] # yields [2] |
768 | to_json [-3.0e17] # yields [-3e+17] |
797 | encode_json [-3.0e17] # yields [-3e+17] |
769 | my $value = 5; to_json [$value] # yields [5] |
798 | my $value = 5; encode_json [$value] # yields [5] |
770 | |
799 | |
771 | # used as string, so dump as string |
800 | # used as string, so dump as string |
772 | print $value; |
801 | print $value; |
773 | to_json [$value] # yields ["5"] |
802 | encode_json [$value] # yields ["5"] |
774 | |
803 | |
775 | # undef becomes null |
804 | # undef becomes null |
776 | to_json [undef] # yields [null] |
805 | encode_json [undef] # yields [null] |
777 | |
806 | |
778 | You can force the type to be a JSON string by stringifying it: |
807 | You can force the type to be a JSON string by stringifying it: |
779 | |
808 | |
780 | my $x = 3.1; # some variable containing a number |
809 | my $x = 3.1; # some variable containing a number |
781 | "$x"; # stringified |
810 | "$x"; # stringified |
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787 | my $x = "3"; # some variable containing a string |
816 | my $x = "3"; # some variable containing a string |
788 | $x += 0; # numify it, ensuring it will be dumped as a number |
817 | $x += 0; # numify it, ensuring it will be dumped as a number |
789 | $x *= 1; # same thing, the choice is yours. |
818 | $x *= 1; # same thing, the choice is yours. |
790 | |
819 | |
791 | You can not currently force the type in other, less obscure, ways. Tell me |
820 | You can not currently force the type in other, less obscure, ways. Tell me |
792 | if you need this capability. |
821 | if you need this capability (but don't forget to explain why its needed |
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822 | :). |
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823 | |
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824 | =back |
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825 | |
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826 | |
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827 | =head1 ENCODING/CODESET FLAG NOTES |
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828 | |
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829 | The interested reader might have seen a number of flags that signify |
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830 | encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be |
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831 | some confusion on what these do, so here is a short comparison: |
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832 | |
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833 | C<utf8> controls wether the JSON text created by C<encode> (and expected |
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834 | by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only |
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835 | control wether C<encode> escapes character values outside their respective |
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836 | codeset range. Neither of these flags conflict with each other, although |
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837 | some combinations make less sense than others. |
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838 | |
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839 | Care has been taken to make all flags symmetrical with respect to |
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840 | C<encode> and C<decode>, that is, texts encoded with any combination of |
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841 | these flag values will be correctly decoded when the same flags are used |
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842 | - in general, if you use different flag settings while encoding vs. when |
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843 | decoding you likely have a bug somewhere. |
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844 | |
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845 | Below comes a verbose discussion of these flags. Note that a "codeset" is |
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846 | simply an abstract set of character-codepoint pairs, while an encoding |
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847 | takes those codepoint numbers and I<encodes> them, in our case into |
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848 | octets. Unicode is (among other things) a codeset, UTF-8 is an encoding, |
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849 | and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at |
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850 | the same time, which can be confusing. |
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851 | |
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852 | =over 4 |
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853 | |
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854 | =item C<utf8> flag disabled |
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855 | |
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856 | When C<utf8> is disabled (the default), then C<encode>/C<decode> generate |
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857 | and expect Unicode strings, that is, characters with high ordinal Unicode |
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858 | values (> 255) will be encoded as such characters, and likewise such |
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859 | characters are decoded as-is, no canges to them will be done, except |
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860 | "(re-)interpreting" them as Unicode codepoints or Unicode characters, |
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861 | respectively (to Perl, these are the same thing in strings unless you do |
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862 | funny/weird/dumb stuff). |
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863 | |
|
|
864 | This is useful when you want to do the encoding yourself (e.g. when you |
|
|
865 | want to have UTF-16 encoded JSON texts) or when some other layer does |
|
|
866 | the encoding for you (for example, when printing to a terminal using a |
|
|
867 | filehandle that transparently encodes to UTF-8 you certainly do NOT want |
|
|
868 | to UTF-8 encode your data first and have Perl encode it another time). |
|
|
869 | |
|
|
870 | =item C<utf8> flag enabled |
|
|
871 | |
|
|
872 | If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all |
|
|
873 | characters using the corresponding UTF-8 multi-byte sequence, and will |
|
|
874 | expect your input strings to be encoded as UTF-8, that is, no "character" |
|
|
875 | of the input string must have any value > 255, as UTF-8 does not allow |
|
|
876 | that. |
|
|
877 | |
|
|
878 | The C<utf8> flag therefore switches between two modes: disabled means you |
|
|
879 | will get a Unicode string in Perl, enabled means you get an UTF-8 encoded |
|
|
880 | octet/binary string in Perl. |
|
|
881 | |
|
|
882 | =item C<latin1> or C<ascii> flags enabled |
|
|
883 | |
|
|
884 | With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters |
|
|
885 | with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining |
|
|
886 | characters as specified by the C<utf8> flag. |
|
|
887 | |
|
|
888 | If C<utf8> is disabled, then the result is also correctly encoded in those |
|
|
889 | character sets (as both are proper subsets of Unicode, meaning that a |
|
|
890 | Unicode string with all character values < 256 is the same thing as a |
|
|
891 | ISO-8859-1 string, and a Unicode string with all character values < 128 is |
|
|
892 | the same thing as an ASCII string in Perl). |
|
|
893 | |
|
|
894 | If C<utf8> is enabled, you still get a correct UTF-8-encoded string, |
|
|
895 | regardless of these flags, just some more characters will be escaped using |
|
|
896 | C<\uXXXX> then before. |
|
|
897 | |
|
|
898 | Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8 |
|
|
899 | encoding, while ASCII-encoded strings are. That is because the ISO-8859-1 |
|
|
900 | encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being |
|
|
901 | a subset of Unicode), while ASCII is. |
|
|
902 | |
|
|
903 | Surprisingly, C<decode> will ignore these flags and so treat all input |
|
|
904 | values as governed by the C<utf8> flag. If it is disabled, this allows you |
|
|
905 | to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of |
|
|
906 | Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings. |
|
|
907 | |
|
|
908 | So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag - |
|
|
909 | they only govern when the JSON output engine escapes a character or not. |
|
|
910 | |
|
|
911 | The main use for C<latin1> is to relatively efficiently store binary data |
|
|
912 | as JSON, at the expense of breaking compatibility with most JSON decoders. |
|
|
913 | |
|
|
914 | The main use for C<ascii> is to force the output to not contain characters |
|
|
915 | with values > 127, which means you can interpret the resulting string |
|
|
916 | as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and |
|
|
917 | 8-bit-encoding, and still get the same data structure back. This is useful |
|
|
918 | when your channel for JSON transfer is not 8-bit clean or the encoding |
|
|
919 | might be mangled in between (e.g. in mail), and works because ASCII is a |
|
|
920 | proper subset of most 8-bit and multibyte encodings in use in the world. |
793 | |
921 | |
794 | =back |
922 | =back |
795 | |
923 | |
796 | |
924 | |
797 | =head1 COMPARISON |
925 | =head1 COMPARISON |
… | |
… | |
801 | problems (or pleasures) I encountered with various existing JSON modules, |
929 | problems (or pleasures) I encountered with various existing JSON modules, |
802 | followed by some benchmark values. JSON::XS was designed not to suffer |
930 | followed by some benchmark values. JSON::XS was designed not to suffer |
803 | from any of these problems or limitations. |
931 | from any of these problems or limitations. |
804 | |
932 | |
805 | =over 4 |
933 | =over 4 |
|
|
934 | |
|
|
935 | =item JSON 2.xx |
|
|
936 | |
|
|
937 | A marvellous piece of engineering, this module either uses JSON::XS |
|
|
938 | directly when available (so will be 100% compatible with it, including |
|
|
939 | speed), or it uses JSON::PP, which is basically JSON::XS translated to |
|
|
940 | Pure Perl, which should be 100% compatible with JSON::XS, just a bit |
|
|
941 | slower. |
|
|
942 | |
|
|
943 | You cannot really lose by using this module, especially as it tries very |
|
|
944 | hard to work even with ancient Perl versions, while JSON::XS does not. |
806 | |
945 | |
807 | =item JSON 1.07 |
946 | =item JSON 1.07 |
808 | |
947 | |
809 | Slow (but very portable, as it is written in pure Perl). |
948 | Slow (but very portable, as it is written in pure Perl). |
810 | |
949 | |
… | |
… | |
881 | =back |
1020 | =back |
882 | |
1021 | |
883 | |
1022 | |
884 | =head2 JSON and YAML |
1023 | =head2 JSON and YAML |
885 | |
1024 | |
886 | You often hear that JSON is a subset (or a close subset) of YAML. This is, |
1025 | You often hear that JSON is a subset of YAML. This is, however, a mass |
887 | however, a mass hysteria and very far from the truth. In general, there is |
1026 | hysteria(*) and very far from the truth. In general, there is no way to |
888 | no way to configure JSON::XS to output a data structure as valid YAML. |
1027 | configure JSON::XS to output a data structure as valid YAML that works for |
|
|
1028 | all cases. |
889 | |
1029 | |
890 | If you really must use JSON::XS to generate YAML, you should use this |
1030 | If you really must use JSON::XS to generate YAML, you should use this |
891 | algorithm (subject to change in future versions): |
1031 | algorithm (subject to change in future versions): |
892 | |
1032 | |
893 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
1033 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
894 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
1034 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
895 | |
1035 | |
896 | This will usually generate JSON texts that also parse as valid |
1036 | This will I<usually> generate JSON texts that also parse as valid |
897 | YAML. Please note that YAML has hardcoded limits on (simple) object key |
1037 | YAML. Please note that YAML has hardcoded limits on (simple) object key |
898 | lengths that JSON doesn't have, so you should make sure that your hash |
1038 | lengths that JSON doesn't have and also has different and incompatible |
|
|
1039 | unicode handling, so you should make sure that your hash keys are |
899 | keys are noticeably shorter than the 1024 characters YAML allows. |
1040 | noticeably shorter than the 1024 "stream characters" YAML allows and that |
|
|
1041 | you do not have codepoints with values outside the Unicode BMP (basic |
|
|
1042 | multilingual page). YAML also does not allow C<\/> sequences in strings |
|
|
1043 | (which JSON::XS does not I<currently> generate). |
900 | |
1044 | |
901 | There might be other incompatibilities that I am not aware of. In general |
1045 | There might be other incompatibilities that I am not aware of (or the YAML |
|
|
1046 | specification has been changed yet again - it does so quite often). In |
902 | you should not try to generate YAML with a JSON generator or vice versa, |
1047 | general you should not try to generate YAML with a JSON generator or vice |
903 | or try to parse JSON with a YAML parser or vice versa: chances are high |
1048 | versa, or try to parse JSON with a YAML parser or vice versa: chances are |
904 | that you will run into severe interoperability problems. |
1049 | high that you will run into severe interoperability problems when you |
|
|
1050 | least expect it. |
|
|
1051 | |
|
|
1052 | =over 4 |
|
|
1053 | |
|
|
1054 | =item (*) |
|
|
1055 | |
|
|
1056 | This is spread actively by the YAML team, however. For many years now they |
|
|
1057 | claim YAML were a superset of JSON, even when proven otherwise. |
|
|
1058 | |
|
|
1059 | Even the author of this manpage was at some point accused of providing |
|
|
1060 | "incorrect" information, despite the evidence presented (claims ranged |
|
|
1061 | from "your documentation contains inaccurate and negative statements about |
|
|
1062 | YAML" (the only negative comment is this footnote, and it didn't exist |
|
|
1063 | back then; the question on which claims were inaccurate was never answered |
|
|
1064 | etc.) to "the YAML spec is not up-to-date" (the *real* and supposedly |
|
|
1065 | JSON-compatible spec is apparently not currently publicly available) |
|
|
1066 | to actual requests to replace this section by *incorrect* information, |
|
|
1067 | suppressing information about the real problem). |
|
|
1068 | |
|
|
1069 | So whenever you are told that YAML was a superset of JSON, first check |
|
|
1070 | wether it is really true (it might be when you check it, but it certainly |
|
|
1071 | was not true when this was written). I would much prefer if the YAML team |
|
|
1072 | would spent their time on actually making JSON compatibility a truth |
|
|
1073 | (JSON, after all, has a very small and simple specification) instead of |
|
|
1074 | trying to lobby/force people into reporting untruths. |
|
|
1075 | |
|
|
1076 | =back |
905 | |
1077 | |
906 | |
1078 | |
907 | =head2 SPEED |
1079 | =head2 SPEED |
908 | |
1080 | |
909 | It seems that JSON::XS is surprisingly fast, as shown in the following |
1081 | It seems that JSON::XS is surprisingly fast, as shown in the following |
… | |
… | |
939 | about three times faster on decoding, and over forty times faster |
1111 | about three times faster on decoding, and over forty times faster |
940 | than JSON, even with pretty-printing and key sorting. It also compares |
1112 | than JSON, even with pretty-printing and key sorting. It also compares |
941 | favourably to Storable for small amounts of data. |
1113 | favourably to Storable for small amounts of data. |
942 | |
1114 | |
943 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
1115 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
944 | search API (http://nanoref.com/yahooapis/mgPdGg): |
1116 | search API (http://dist.schmorp.de/misc/yahoo.json). |
945 | |
1117 | |
946 | module | encode | decode | |
1118 | module | encode | decode | |
947 | -----------|------------|------------| |
1119 | -----------|------------|------------| |
948 | JSON 1.x | 55.260 | 34.971 | |
1120 | JSON 1.x | 55.260 | 34.971 | |
949 | JSON::DWIW | 825.228 | 1082.513 | |
1121 | JSON::DWIW | 825.228 | 1082.513 | |
… | |
… | |
986 | |
1158 | |
987 | Third, JSON::XS recurses using the C stack when decoding objects and |
1159 | Third, JSON::XS recurses using the C stack when decoding objects and |
988 | arrays. The C stack is a limited resource: for instance, on my amd64 |
1160 | arrays. The C stack is a limited resource: for instance, on my amd64 |
989 | machine with 8MB of stack size I can decode around 180k nested arrays but |
1161 | machine with 8MB of stack size I can decode around 180k nested arrays but |
990 | only 14k nested JSON objects (due to perl itself recursing deeply on croak |
1162 | only 14k nested JSON objects (due to perl itself recursing deeply on croak |
991 | to free the temporary). If that is exceeded, the program crashes. to be |
1163 | to free the temporary). If that is exceeded, the program crashes. To be |
992 | conservative, the default nesting limit is set to 512. If your process |
1164 | conservative, the default nesting limit is set to 512. If your process |
993 | has a smaller stack, you should adjust this setting accordingly with the |
1165 | has a smaller stack, you should adjust this setting accordingly with the |
994 | C<max_depth> method. |
1166 | C<max_depth> method. |
995 | |
1167 | |
996 | And last but least, something else could bomb you that I forgot to think |
1168 | Something else could bomb you, too, that I forgot to think of. In that |
997 | of. In that case, you get to keep the pieces. I am always open for hints, |
1169 | case, you get to keep the pieces. I am always open for hints, though... |
998 | though... |
1170 | |
|
|
1171 | Also keep in mind that JSON::XS might leak contents of your Perl data |
|
|
1172 | structures in its error messages, so when you serialise sensitive |
|
|
1173 | information you might want to make sure that exceptions thrown by JSON::XS |
|
|
1174 | will not end up in front of untrusted eyes. |
999 | |
1175 | |
1000 | If you are using JSON::XS to return packets to consumption |
1176 | If you are using JSON::XS to return packets to consumption |
1001 | by JavaScript scripts in a browser you should have a look at |
1177 | by JavaScript scripts in a browser you should have a look at |
1002 | L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether |
1178 | L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether |
1003 | you are vulnerable to some common attack vectors (which really are browser |
1179 | you are vulnerable to some common attack vectors (which really are browser |
1004 | design bugs, but it is still you who will have to deal with it, as major |
1180 | design bugs, but it is still you who will have to deal with it, as major |
1005 | browser developers care only for features, not about doing security |
1181 | browser developers care only for features, not about getting security |
1006 | right). |
1182 | right). |
1007 | |
1183 | |
1008 | |
1184 | |
1009 | =head1 THREADS |
1185 | =head1 THREADS |
1010 | |
1186 | |