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1 | =head1 NAME |
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2 | |
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3 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
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4 | |
1 | =encoding utf-8 |
5 | =encoding utf-8 |
2 | |
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3 | =head1 NAME |
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4 | |
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5 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
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6 | |
6 | |
7 | 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 |
8 | (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) |
8 | (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) |
9 | |
9 | |
10 | =head1 SYNOPSIS |
10 | =head1 SYNOPSIS |
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37 | 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 |
38 | 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. |
39 | |
39 | |
40 | Beginning with version 2.0 of the JSON module, when both JSON and |
40 | Beginning with version 2.0 of the JSON module, when both JSON and |
41 | JSON::XS are installed, then JSON will fall back on JSON::XS (this can be |
41 | JSON::XS are installed, then JSON will fall back on JSON::XS (this can be |
42 | overriden) with no overhead due to emulation (by inheritign constructor |
42 | overridden) with no overhead due to emulation (by inheriting constructor |
43 | and methods). If JSON::XS is not available, it will fall back to the |
43 | and methods). If JSON::XS is not available, it will fall back to the |
44 | compatible JSON::PP module as backend, so using JSON instead of JSON::XS |
44 | compatible JSON::PP module as backend, so using JSON instead of JSON::XS |
45 | gives you a portable JSON API that can be fast when you need and doesn't |
45 | gives you a portable JSON API that can be fast when you need and doesn't |
46 | require a C compiler when that is a problem. |
46 | require a C compiler when that is a problem. |
47 | |
47 | |
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49 | 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 |
50 | 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 |
51 | their maintainers are unresponsive, gone missing, or not listening to bug |
51 | their maintainers are unresponsive, gone missing, or not listening to bug |
52 | reports for other reasons. |
52 | reports for other reasons. |
53 | |
53 | |
54 | See COMPARISON, below, for a comparison to some other JSON modules. |
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55 | |
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56 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
54 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
57 | vice versa. |
55 | vice versa. |
58 | |
56 | |
59 | =head2 FEATURES |
57 | =head2 FEATURES |
60 | |
58 | |
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65 | This module knows how to handle Unicode, documents how and when it does |
63 | This module knows how to handle Unicode, documents how and when it does |
66 | so, and even documents what "correct" means. |
64 | so, and even documents what "correct" means. |
67 | |
65 | |
68 | =item * round-trip integrity |
66 | =item * round-trip integrity |
69 | |
67 | |
70 | When you serialise a perl data structure using only datatypes supported |
68 | When you serialise a perl data structure using only data types supported |
71 | by JSON, the deserialised data structure is identical on the Perl level. |
69 | by JSON and Perl, the deserialised data structure is identical on the Perl |
72 | (e.g. the string "2.0" doesn't suddenly become "2" just because it looks |
70 | level. (e.g. the string "2.0" doesn't suddenly become "2" just because |
73 | like a number). There minor I<are> exceptions to this, read the MAPPING |
71 | it looks like a number). There I<are> minor exceptions to this, read the |
74 | section below to learn about those. |
72 | MAPPING section below to learn about those. |
75 | |
73 | |
76 | =item * strict checking of JSON correctness |
74 | =item * strict checking of JSON correctness |
77 | |
75 | |
78 | There is no guessing, no generating of illegal JSON texts by default, |
76 | There is no guessing, no generating of illegal JSON texts by default, |
79 | and only JSON is accepted as input by default (the latter is a security |
77 | and only JSON is accepted as input by default (the latter is a security |
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84 | Compared to other JSON modules and other serialisers such as Storable, |
82 | Compared to other JSON modules and other serialisers such as Storable, |
85 | this module usually compares favourably in terms of speed, too. |
83 | this module usually compares favourably in terms of speed, too. |
86 | |
84 | |
87 | =item * simple to use |
85 | =item * simple to use |
88 | |
86 | |
89 | This module has both a simple functional interface as well as an objetc |
87 | This module has both a simple functional interface as well as an object |
90 | oriented interface interface. |
88 | oriented interface. |
91 | |
89 | |
92 | =item * reasonably versatile output formats |
90 | =item * reasonably versatile output formats |
93 | |
91 | |
94 | You can choose between the most compact guaranteed-single-line format |
92 | You can choose between the most compact guaranteed-single-line format |
95 | possible (nice for simple line-based protocols), a pure-ascii format |
93 | possible (nice for simple line-based protocols), a pure-ASCII format |
96 | (for when your transport is not 8-bit clean, still supports the whole |
94 | (for when your transport is not 8-bit clean, still supports the whole |
97 | Unicode range), or a pretty-printed format (for when you want to read that |
95 | Unicode range), or a pretty-printed format (for when you want to read that |
98 | stuff). Or you can combine those features in whatever way you like. |
96 | stuff). Or you can combine those features in whatever way you like. |
99 | |
97 | |
100 | =back |
98 | =back |
101 | |
99 | |
102 | =cut |
100 | =cut |
103 | |
101 | |
104 | package JSON::XS; |
102 | package JSON::XS; |
105 | |
103 | |
106 | use strict; |
104 | use common::sense; |
107 | |
105 | |
108 | our $VERSION = '2.01'; |
106 | our $VERSION = 2.34; |
109 | our @ISA = qw(Exporter); |
107 | our @ISA = qw(Exporter); |
110 | |
108 | |
111 | our @EXPORT = qw(encode_json decode_json to_json from_json); |
109 | our @EXPORT = qw(encode_json decode_json); |
112 | |
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113 | sub to_json($) { |
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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 | } |
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122 | |
110 | |
123 | use Exporter; |
111 | use Exporter; |
124 | use XSLoader; |
112 | use XSLoader; |
125 | |
113 | |
126 | =head1 FUNCTIONAL INTERFACE |
114 | =head1 FUNCTIONAL INTERFACE |
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137 | |
125 | |
138 | This function call is functionally identical to: |
126 | This function call is functionally identical to: |
139 | |
127 | |
140 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
128 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
141 | |
129 | |
142 | except being faster. |
130 | Except being faster. |
143 | |
131 | |
144 | =item $perl_scalar = decode_json $json_text |
132 | =item $perl_scalar = decode_json $json_text |
145 | |
133 | |
146 | The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries |
134 | The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries |
147 | to parse that as an UTF-8 encoded JSON text, returning the resulting |
135 | to parse that as an UTF-8 encoded JSON text, returning the resulting |
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149 | |
137 | |
150 | This function call is functionally identical to: |
138 | This function call is functionally identical to: |
151 | |
139 | |
152 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
140 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
153 | |
141 | |
154 | except being faster. |
142 | Except being faster. |
155 | |
143 | |
156 | =item $is_boolean = JSON::XS::is_bool $scalar |
144 | =item $is_boolean = JSON::XS::is_bool $scalar |
157 | |
145 | |
158 | Returns true if the passed scalar represents either JSON::XS::true or |
146 | Returns true if the passed scalar represents either JSON::XS::true or |
159 | JSON::XS::false, two constants that act like C<1> and C<0>, respectively |
147 | JSON::XS::false, two constants that act like C<1> and C<0>, respectively |
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197 | |
185 | |
198 | If you didn't know about that flag, just the better, pretend it doesn't |
186 | If you didn't know about that flag, just the better, pretend it doesn't |
199 | exist. |
187 | exist. |
200 | |
188 | |
201 | =item 4. A "Unicode String" is simply a string where each character can be |
189 | =item 4. A "Unicode String" is simply a string where each character can be |
202 | validly interpreted as a Unicode codepoint. |
190 | validly interpreted as a Unicode code point. |
203 | |
191 | |
204 | If you have UTF-8 encoded data, it is no longer a Unicode string, but a |
192 | If you have UTF-8 encoded data, it is no longer a Unicode string, but a |
205 | Unicode string encoded in UTF-8, giving you a binary string. |
193 | Unicode string encoded in UTF-8, giving you a binary string. |
206 | |
194 | |
207 | =item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string. |
195 | =item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string. |
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245 | |
233 | |
246 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
234 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
247 | characters unless required by the JSON syntax or other flags. This results |
235 | characters unless required by the JSON syntax or other flags. This results |
248 | in a faster and more compact format. |
236 | in a faster and more compact format. |
249 | |
237 | |
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238 | See also the section I<ENCODING/CODESET FLAG NOTES> later in this |
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239 | document. |
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240 | |
250 | The main use for this flag is to produce JSON texts that can be |
241 | The main use for this flag is to produce JSON texts that can be |
251 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
242 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
252 | contain any 8 bit characters. |
243 | contain any 8 bit characters. |
253 | |
244 | |
254 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
245 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
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265 | will not be affected in any way by this flag, as C<decode> by default |
256 | will not be affected in any way by this flag, as C<decode> by default |
266 | expects Unicode, which is a strict superset of latin1. |
257 | expects Unicode, which is a strict superset of latin1. |
267 | |
258 | |
268 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
259 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
269 | characters unless required by the JSON syntax or other flags. |
260 | characters unless required by the JSON syntax or other flags. |
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261 | |
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262 | See also the section I<ENCODING/CODESET FLAG NOTES> later in this |
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263 | document. |
270 | |
264 | |
271 | The main use for this flag is efficiently encoding binary data as JSON |
265 | The main use for this flag is efficiently encoding binary data as JSON |
272 | text, as most octets will not be escaped, resulting in a smaller encoded |
266 | text, as most octets will not be escaped, resulting in a smaller encoded |
273 | size. The disadvantage is that the resulting JSON text is encoded |
267 | size. The disadvantage is that the resulting JSON text is encoded |
274 | in latin1 (and must correctly be treated as such when storing and |
268 | in latin1 (and must correctly be treated as such when storing and |
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293 | |
287 | |
294 | If C<$enable> is false, then the C<encode> method will return the JSON |
288 | If C<$enable> is false, then the C<encode> method will return the JSON |
295 | string as a (non-encoded) Unicode string, while C<decode> expects thus a |
289 | string as a (non-encoded) Unicode string, while C<decode> expects thus a |
296 | Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs |
290 | Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs |
297 | to be done yourself, e.g. using the Encode module. |
291 | to be done yourself, e.g. using the Encode module. |
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292 | |
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293 | See also the section I<ENCODING/CODESET FLAG NOTES> later in this |
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294 | document. |
298 | |
295 | |
299 | Example, output UTF-16BE-encoded JSON: |
296 | Example, output UTF-16BE-encoded JSON: |
300 | |
297 | |
301 | use Encode; |
298 | use Encode; |
302 | $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
299 | $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
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425 | If C<$enable> is true (or missing), then the C<encode> method will output JSON objects |
422 | If C<$enable> is true (or missing), then the C<encode> method will output JSON objects |
426 | by sorting their keys. This is adding a comparatively high overhead. |
423 | by sorting their keys. This is adding a comparatively high overhead. |
427 | |
424 | |
428 | If C<$enable> is false, then the C<encode> method will output key-value |
425 | If C<$enable> is false, then the C<encode> method will output key-value |
429 | pairs in the order Perl stores them (which will likely change between runs |
426 | pairs in the order Perl stores them (which will likely change between runs |
430 | of the same script). |
427 | of the same script, and can change even within the same run from 5.18 |
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428 | onwards). |
431 | |
429 | |
432 | This option is useful if you want the same data structure to be encoded as |
430 | This option is useful if you want the same data structure to be encoded as |
433 | the same JSON text (given the same overall settings). If it is disabled, |
431 | the same JSON text (given the same overall settings). If it is disabled, |
434 | the same hash might be encoded differently even if contains the same data, |
432 | the same hash might be encoded differently even if contains the same data, |
435 | as key-value pairs have no inherent ordering in Perl. |
433 | as key-value pairs have no inherent ordering in Perl. |
436 | |
434 | |
437 | This setting has no effect when decoding JSON texts. |
435 | This setting has no effect when decoding JSON texts. |
438 | |
436 | |
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437 | This setting has currently no effect on tied hashes. |
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438 | |
439 | =item $json = $json->allow_nonref ([$enable]) |
439 | =item $json = $json->allow_nonref ([$enable]) |
440 | |
440 | |
441 | =item $enabled = $json->get_allow_nonref |
441 | =item $enabled = $json->get_allow_nonref |
442 | |
442 | |
443 | If C<$enable> is true (or missing), then the C<encode> method can convert a |
443 | If C<$enable> is true (or missing), then the C<encode> method can convert a |
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453 | Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>, |
453 | Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>, |
454 | resulting in an invalid JSON text: |
454 | resulting in an invalid JSON text: |
455 | |
455 | |
456 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
456 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
457 | => "Hello, World!" |
457 | => "Hello, World!" |
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458 | |
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459 | =item $json = $json->allow_unknown ([$enable]) |
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460 | |
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461 | =item $enabled = $json->get_allow_unknown |
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462 | |
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463 | If C<$enable> is true (or missing), then C<encode> will I<not> throw an |
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464 | exception when it encounters values it cannot represent in JSON (for |
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465 | example, filehandles) but instead will encode a JSON C<null> value. Note |
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466 | that blessed objects are not included here and are handled separately by |
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467 | c<allow_nonref>. |
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468 | |
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469 | If C<$enable> is false (the default), then C<encode> will throw an |
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470 | exception when it encounters anything it cannot encode as JSON. |
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471 | |
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472 | This option does not affect C<decode> in any way, and it is recommended to |
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473 | leave it off unless you know your communications partner. |
458 | |
474 | |
459 | =item $json = $json->allow_blessed ([$enable]) |
475 | =item $json = $json->allow_blessed ([$enable]) |
460 | |
476 | |
461 | =item $enabled = $json->get_allow_blessed |
477 | =item $enabled = $json->get_allow_blessed |
462 | |
478 | |
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603 | =item $json = $json->max_depth ([$maximum_nesting_depth]) |
619 | =item $json = $json->max_depth ([$maximum_nesting_depth]) |
604 | |
620 | |
605 | =item $max_depth = $json->get_max_depth |
621 | =item $max_depth = $json->get_max_depth |
606 | |
622 | |
607 | Sets the maximum nesting level (default C<512>) accepted while encoding |
623 | Sets the maximum nesting level (default C<512>) accepted while encoding |
608 | or decoding. If the JSON text or Perl data structure has an equal or |
624 | or decoding. If a higher nesting level is detected in JSON text or a Perl |
609 | higher nesting level then this limit, then the encoder and decoder will |
625 | data structure, then the encoder and decoder will stop and croak at that |
610 | stop and croak at that point. |
626 | point. |
611 | |
627 | |
612 | Nesting level is defined by number of hash- or arrayrefs that the encoder |
628 | Nesting level is defined by number of hash- or arrayrefs that the encoder |
613 | needs to traverse to reach a given point or the number of C<{> or C<[> |
629 | needs to traverse to reach a given point or the number of C<{> or C<[> |
614 | characters without their matching closing parenthesis crossed to reach a |
630 | characters without their matching closing parenthesis crossed to reach a |
615 | given character in a string. |
631 | given character in a string. |
616 | |
632 | |
617 | Setting the maximum depth to one disallows any nesting, so that ensures |
633 | Setting the maximum depth to one disallows any nesting, so that ensures |
618 | that the object is only a single hash/object or array. |
634 | that the object is only a single hash/object or array. |
619 | |
635 | |
620 | The argument to C<max_depth> will be rounded up to the next highest power |
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621 | of two. If no argument is given, the highest possible setting will be |
636 | If no argument is given, the highest possible setting will be used, which |
622 | used, which is rarely useful. |
637 | is rarely useful. |
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638 | |
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639 | Note that nesting is implemented by recursion in C. The default value has |
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640 | been chosen to be as large as typical operating systems allow without |
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641 | crashing. |
623 | |
642 | |
624 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
643 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
625 | |
644 | |
626 | =item $json = $json->max_size ([$maximum_string_size]) |
645 | =item $json = $json->max_size ([$maximum_string_size]) |
627 | |
646 | |
628 | =item $max_size = $json->get_max_size |
647 | =item $max_size = $json->get_max_size |
629 | |
648 | |
630 | Set the maximum length a JSON text may have (in bytes) where decoding is |
649 | Set the maximum length a JSON text may have (in bytes) where decoding is |
631 | being attempted. The default is C<0>, meaning no limit. When C<decode> |
650 | being attempted. The default is C<0>, meaning no limit. When C<decode> |
632 | is called on a string longer then this number of characters it will not |
651 | is called on a string that is longer then this many bytes, it will not |
633 | attempt to decode the string but throw an exception. This setting has no |
652 | attempt to decode the string but throw an exception. This setting has no |
634 | effect on C<encode> (yet). |
653 | effect on C<encode> (yet). |
635 | |
654 | |
636 | The argument to C<max_size> will be rounded up to the next B<highest> |
655 | If no argument is given, the limit check will be deactivated (same as when |
637 | power of two (so may be more than requested). If no argument is given, the |
656 | C<0> is specified). |
638 | limit check will be deactivated (same as when C<0> is specified). |
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639 | |
657 | |
640 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
658 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
641 | |
659 | |
642 | =item $json_text = $json->encode ($perl_scalar) |
660 | =item $json_text = $json->encode ($perl_scalar) |
643 | |
661 | |
644 | Converts the given Perl data structure (a simple scalar or a reference |
662 | Converts the given Perl value or data structure to its JSON |
645 | to a hash or array) to its JSON representation. Simple scalars will be |
663 | representation. Croaks on error. |
646 | converted into JSON string or number sequences, while references to arrays |
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647 | become JSON arrays and references to hashes become JSON objects. Undefined |
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648 | Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true> |
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649 | nor C<false> values will be generated. |
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650 | |
664 | |
651 | =item $perl_scalar = $json->decode ($json_text) |
665 | =item $perl_scalar = $json->decode ($json_text) |
652 | |
666 | |
653 | The opposite of C<encode>: expects a JSON text and tries to parse it, |
667 | The opposite of C<encode>: expects a JSON text and tries to parse it, |
654 | returning the resulting simple scalar or reference. Croaks on error. |
668 | returning the resulting simple scalar or reference. Croaks on error. |
655 | |
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656 | JSON numbers and strings become simple Perl scalars. JSON arrays become |
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657 | Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes |
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658 | C<1>, C<false> becomes C<0> and C<null> becomes C<undef>. |
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659 | |
669 | |
660 | =item ($perl_scalar, $characters) = $json->decode_prefix ($json_text) |
670 | =item ($perl_scalar, $characters) = $json->decode_prefix ($json_text) |
661 | |
671 | |
662 | This works like the C<decode> method, but instead of raising an exception |
672 | This works like the C<decode> method, but instead of raising an exception |
663 | when there is trailing garbage after the first JSON object, it will |
673 | when there is trailing garbage after the first JSON object, it will |
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670 | |
680 | |
671 | JSON::XS->new->decode_prefix ("[1] the tail") |
681 | JSON::XS->new->decode_prefix ("[1] the tail") |
672 | => ([], 3) |
682 | => ([], 3) |
673 | |
683 | |
674 | =back |
684 | =back |
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685 | |
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686 | |
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687 | =head1 INCREMENTAL PARSING |
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688 | |
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689 | In some cases, there is the need for incremental parsing of JSON |
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690 | texts. While this module always has to keep both JSON text and resulting |
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691 | Perl data structure in memory at one time, it does allow you to parse a |
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692 | JSON stream incrementally. It does so by accumulating text until it has |
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693 | a full JSON object, which it then can decode. This process is similar to |
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694 | using C<decode_prefix> to see if a full JSON object is available, but |
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695 | is much more efficient (and can be implemented with a minimum of method |
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696 | calls). |
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697 | |
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698 | JSON::XS will only attempt to parse the JSON text once it is sure it |
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699 | has enough text to get a decisive result, using a very simple but |
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700 | truly incremental parser. This means that it sometimes won't stop as |
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701 | early as the full parser, for example, it doesn't detect mismatched |
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702 | parentheses. The only thing it guarantees is that it starts decoding as |
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703 | soon as a syntactically valid JSON text has been seen. This means you need |
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704 | to set resource limits (e.g. C<max_size>) to ensure the parser will stop |
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705 | parsing in the presence if syntax errors. |
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706 | |
|
|
707 | The following methods implement this incremental parser. |
|
|
708 | |
|
|
709 | =over 4 |
|
|
710 | |
|
|
711 | =item [void, scalar or list context] = $json->incr_parse ([$string]) |
|
|
712 | |
|
|
713 | This is the central parsing function. It can both append new text and |
|
|
714 | extract objects from the stream accumulated so far (both of these |
|
|
715 | functions are optional). |
|
|
716 | |
|
|
717 | If C<$string> is given, then this string is appended to the already |
|
|
718 | existing JSON fragment stored in the C<$json> object. |
|
|
719 | |
|
|
720 | After that, if the function is called in void context, it will simply |
|
|
721 | return without doing anything further. This can be used to add more text |
|
|
722 | in as many chunks as you want. |
|
|
723 | |
|
|
724 | If the method is called in scalar context, then it will try to extract |
|
|
725 | exactly I<one> JSON object. If that is successful, it will return this |
|
|
726 | object, otherwise it will return C<undef>. If there is a parse error, |
|
|
727 | this method will croak just as C<decode> would do (one can then use |
|
|
728 | C<incr_skip> to skip the erroneous part). This is the most common way of |
|
|
729 | using the method. |
|
|
730 | |
|
|
731 | And finally, in list context, it will try to extract as many objects |
|
|
732 | from the stream as it can find and return them, or the empty list |
|
|
733 | otherwise. For this to work, there must be no separators between the JSON |
|
|
734 | objects or arrays, instead they must be concatenated back-to-back. If |
|
|
735 | an error occurs, an exception will be raised as in the scalar context |
|
|
736 | case. Note that in this case, any previously-parsed JSON texts will be |
|
|
737 | lost. |
|
|
738 | |
|
|
739 | Example: Parse some JSON arrays/objects in a given string and return |
|
|
740 | them. |
|
|
741 | |
|
|
742 | my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]"); |
|
|
743 | |
|
|
744 | =item $lvalue_string = $json->incr_text |
|
|
745 | |
|
|
746 | This method returns the currently stored JSON fragment as an lvalue, that |
|
|
747 | is, you can manipulate it. This I<only> works when a preceding call to |
|
|
748 | C<incr_parse> in I<scalar context> successfully returned an object. Under |
|
|
749 | all other circumstances you must not call this function (I mean it. |
|
|
750 | although in simple tests it might actually work, it I<will> fail under |
|
|
751 | real world conditions). As a special exception, you can also call this |
|
|
752 | method before having parsed anything. |
|
|
753 | |
|
|
754 | This function is useful in two cases: a) finding the trailing text after a |
|
|
755 | JSON object or b) parsing multiple JSON objects separated by non-JSON text |
|
|
756 | (such as commas). |
|
|
757 | |
|
|
758 | =item $json->incr_skip |
|
|
759 | |
|
|
760 | This will reset the state of the incremental parser and will remove |
|
|
761 | the parsed text from the input buffer so far. This is useful after |
|
|
762 | C<incr_parse> died, in which case the input buffer and incremental parser |
|
|
763 | state is left unchanged, to skip the text parsed so far and to reset the |
|
|
764 | parse state. |
|
|
765 | |
|
|
766 | The difference to C<incr_reset> is that only text until the parse error |
|
|
767 | occurred is removed. |
|
|
768 | |
|
|
769 | =item $json->incr_reset |
|
|
770 | |
|
|
771 | This completely resets the incremental parser, that is, after this call, |
|
|
772 | it will be as if the parser had never parsed anything. |
|
|
773 | |
|
|
774 | This is useful if you want to repeatedly parse JSON objects and want to |
|
|
775 | ignore any trailing data, which means you have to reset the parser after |
|
|
776 | each successful decode. |
|
|
777 | |
|
|
778 | =back |
|
|
779 | |
|
|
780 | =head2 LIMITATIONS |
|
|
781 | |
|
|
782 | All options that affect decoding are supported, except |
|
|
783 | C<allow_nonref>. The reason for this is that it cannot be made to |
|
|
784 | work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate |
|
|
785 | them back to back and still decode them perfectly. This does not hold true |
|
|
786 | for JSON numbers, however. |
|
|
787 | |
|
|
788 | For example, is the string C<1> a single JSON number, or is it simply the |
|
|
789 | start of C<12>? Or is C<12> a single JSON number, or the concatenation |
|
|
790 | of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS |
|
|
791 | takes the conservative route and disallows this case. |
|
|
792 | |
|
|
793 | =head2 EXAMPLES |
|
|
794 | |
|
|
795 | Some examples will make all this clearer. First, a simple example that |
|
|
796 | works similarly to C<decode_prefix>: We want to decode the JSON object at |
|
|
797 | the start of a string and identify the portion after the JSON object: |
|
|
798 | |
|
|
799 | my $text = "[1,2,3] hello"; |
|
|
800 | |
|
|
801 | my $json = new JSON::XS; |
|
|
802 | |
|
|
803 | my $obj = $json->incr_parse ($text) |
|
|
804 | or die "expected JSON object or array at beginning of string"; |
|
|
805 | |
|
|
806 | my $tail = $json->incr_text; |
|
|
807 | # $tail now contains " hello" |
|
|
808 | |
|
|
809 | Easy, isn't it? |
|
|
810 | |
|
|
811 | Now for a more complicated example: Imagine a hypothetical protocol where |
|
|
812 | you read some requests from a TCP stream, and each request is a JSON |
|
|
813 | array, without any separation between them (in fact, it is often useful to |
|
|
814 | use newlines as "separators", as these get interpreted as whitespace at |
|
|
815 | the start of the JSON text, which makes it possible to test said protocol |
|
|
816 | with C<telnet>...). |
|
|
817 | |
|
|
818 | Here is how you'd do it (it is trivial to write this in an event-based |
|
|
819 | manner): |
|
|
820 | |
|
|
821 | my $json = new JSON::XS; |
|
|
822 | |
|
|
823 | # read some data from the socket |
|
|
824 | while (sysread $socket, my $buf, 4096) { |
|
|
825 | |
|
|
826 | # split and decode as many requests as possible |
|
|
827 | for my $request ($json->incr_parse ($buf)) { |
|
|
828 | # act on the $request |
|
|
829 | } |
|
|
830 | } |
|
|
831 | |
|
|
832 | Another complicated example: Assume you have a string with JSON objects |
|
|
833 | or arrays, all separated by (optional) comma characters (e.g. C<[1],[2], |
|
|
834 | [3]>). To parse them, we have to skip the commas between the JSON texts, |
|
|
835 | and here is where the lvalue-ness of C<incr_text> comes in useful: |
|
|
836 | |
|
|
837 | my $text = "[1],[2], [3]"; |
|
|
838 | my $json = new JSON::XS; |
|
|
839 | |
|
|
840 | # void context, so no parsing done |
|
|
841 | $json->incr_parse ($text); |
|
|
842 | |
|
|
843 | # now extract as many objects as possible. note the |
|
|
844 | # use of scalar context so incr_text can be called. |
|
|
845 | while (my $obj = $json->incr_parse) { |
|
|
846 | # do something with $obj |
|
|
847 | |
|
|
848 | # now skip the optional comma |
|
|
849 | $json->incr_text =~ s/^ \s* , //x; |
|
|
850 | } |
|
|
851 | |
|
|
852 | Now lets go for a very complex example: Assume that you have a gigantic |
|
|
853 | JSON array-of-objects, many gigabytes in size, and you want to parse it, |
|
|
854 | but you cannot load it into memory fully (this has actually happened in |
|
|
855 | the real world :). |
|
|
856 | |
|
|
857 | Well, you lost, you have to implement your own JSON parser. But JSON::XS |
|
|
858 | can still help you: You implement a (very simple) array parser and let |
|
|
859 | JSON decode the array elements, which are all full JSON objects on their |
|
|
860 | own (this wouldn't work if the array elements could be JSON numbers, for |
|
|
861 | example): |
|
|
862 | |
|
|
863 | my $json = new JSON::XS; |
|
|
864 | |
|
|
865 | # open the monster |
|
|
866 | open my $fh, "<bigfile.json" |
|
|
867 | or die "bigfile: $!"; |
|
|
868 | |
|
|
869 | # first parse the initial "[" |
|
|
870 | for (;;) { |
|
|
871 | sysread $fh, my $buf, 65536 |
|
|
872 | or die "read error: $!"; |
|
|
873 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
874 | |
|
|
875 | # Exit the loop once we found and removed(!) the initial "[". |
|
|
876 | # In essence, we are (ab-)using the $json object as a simple scalar |
|
|
877 | # we append data to. |
|
|
878 | last if $json->incr_text =~ s/^ \s* \[ //x; |
|
|
879 | } |
|
|
880 | |
|
|
881 | # now we have the skipped the initial "[", so continue |
|
|
882 | # parsing all the elements. |
|
|
883 | for (;;) { |
|
|
884 | # in this loop we read data until we got a single JSON object |
|
|
885 | for (;;) { |
|
|
886 | if (my $obj = $json->incr_parse) { |
|
|
887 | # do something with $obj |
|
|
888 | last; |
|
|
889 | } |
|
|
890 | |
|
|
891 | # add more data |
|
|
892 | sysread $fh, my $buf, 65536 |
|
|
893 | or die "read error: $!"; |
|
|
894 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
895 | } |
|
|
896 | |
|
|
897 | # in this loop we read data until we either found and parsed the |
|
|
898 | # separating "," between elements, or the final "]" |
|
|
899 | for (;;) { |
|
|
900 | # first skip whitespace |
|
|
901 | $json->incr_text =~ s/^\s*//; |
|
|
902 | |
|
|
903 | # if we find "]", we are done |
|
|
904 | if ($json->incr_text =~ s/^\]//) { |
|
|
905 | print "finished.\n"; |
|
|
906 | exit; |
|
|
907 | } |
|
|
908 | |
|
|
909 | # if we find ",", we can continue with the next element |
|
|
910 | if ($json->incr_text =~ s/^,//) { |
|
|
911 | last; |
|
|
912 | } |
|
|
913 | |
|
|
914 | # if we find anything else, we have a parse error! |
|
|
915 | if (length $json->incr_text) { |
|
|
916 | die "parse error near ", $json->incr_text; |
|
|
917 | } |
|
|
918 | |
|
|
919 | # else add more data |
|
|
920 | sysread $fh, my $buf, 65536 |
|
|
921 | or die "read error: $!"; |
|
|
922 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
923 | } |
|
|
924 | |
|
|
925 | This is a complex example, but most of the complexity comes from the fact |
|
|
926 | that we are trying to be correct (bear with me if I am wrong, I never ran |
|
|
927 | the above example :). |
|
|
928 | |
675 | |
929 | |
676 | |
930 | |
677 | =head1 MAPPING |
931 | =head1 MAPPING |
678 | |
932 | |
679 | This section describes how JSON::XS maps Perl values to JSON values and |
933 | This section describes how JSON::XS maps Perl values to JSON values and |
… | |
… | |
716 | If the number consists of digits only, JSON::XS will try to represent |
970 | If the number consists of digits only, JSON::XS will try to represent |
717 | it as an integer value. If that fails, it will try to represent it as |
971 | it as an integer value. If that fails, it will try to represent it as |
718 | a numeric (floating point) value if that is possible without loss of |
972 | a numeric (floating point) value if that is possible without loss of |
719 | precision. Otherwise it will preserve the number as a string value (in |
973 | precision. Otherwise it will preserve the number as a string value (in |
720 | which case you lose roundtripping ability, as the JSON number will be |
974 | which case you lose roundtripping ability, as the JSON number will be |
721 | re-encoded toa JSON string). |
975 | re-encoded to a JSON string). |
722 | |
976 | |
723 | Numbers containing a fractional or exponential part will always be |
977 | Numbers containing a fractional or exponential part will always be |
724 | represented as numeric (floating point) values, possibly at a loss of |
978 | represented as numeric (floating point) values, possibly at a loss of |
725 | precision (in which case you might lose perfect roundtripping ability, but |
979 | precision (in which case you might lose perfect roundtripping ability, but |
726 | the JSON number will still be re-encoded as a JSON number). |
980 | the JSON number will still be re-encoded as a JSON number). |
|
|
981 | |
|
|
982 | Note that precision is not accuracy - binary floating point values cannot |
|
|
983 | represent most decimal fractions exactly, and when converting from and to |
|
|
984 | floating point, JSON::XS only guarantees precision up to but not including |
|
|
985 | the least significant bit. |
727 | |
986 | |
728 | =item true, false |
987 | =item true, false |
729 | |
988 | |
730 | These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, |
989 | These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, |
731 | respectively. They are overloaded to act almost exactly like the numbers |
990 | respectively. They are overloaded to act almost exactly like the numbers |
… | |
… | |
768 | Other unblessed references are generally not allowed and will cause an |
1027 | Other unblessed references are generally not allowed and will cause an |
769 | exception to be thrown, except for references to the integers C<0> and |
1028 | exception to be thrown, except for references to the integers C<0> and |
770 | C<1>, which get turned into C<false> and C<true> atoms in JSON. You can |
1029 | C<1>, which get turned into C<false> and C<true> atoms in JSON. You can |
771 | also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. |
1030 | also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. |
772 | |
1031 | |
773 | encode_json [\0,JSON::XS::true] # yields [false,true] |
1032 | encode_json [\0, JSON::XS::true] # yields [false,true] |
774 | |
1033 | |
775 | =item JSON::XS::true, JSON::XS::false |
1034 | =item JSON::XS::true, JSON::XS::false |
776 | |
1035 | |
777 | These special values become JSON true and JSON false values, |
1036 | These special values become JSON true and JSON false values, |
778 | respectively. You can also use C<\1> and C<\0> directly if you want. |
1037 | respectively. You can also use C<\1> and C<\0> directly if you want. |
… | |
… | |
816 | my $x = "3"; # some variable containing a string |
1075 | my $x = "3"; # some variable containing a string |
817 | $x += 0; # numify it, ensuring it will be dumped as a number |
1076 | $x += 0; # numify it, ensuring it will be dumped as a number |
818 | $x *= 1; # same thing, the choice is yours. |
1077 | $x *= 1; # same thing, the choice is yours. |
819 | |
1078 | |
820 | You can not currently force the type in other, less obscure, ways. Tell me |
1079 | You can not currently force the type in other, less obscure, ways. Tell me |
821 | if you need this capability (but don't forget to explain why its needed |
1080 | if you need this capability (but don't forget to explain why it's needed |
822 | :). |
1081 | :). |
|
|
1082 | |
|
|
1083 | Note that numerical precision has the same meaning as under Perl (so |
|
|
1084 | binary to decimal conversion follows the same rules as in Perl, which |
|
|
1085 | can differ to other languages). Also, your perl interpreter might expose |
|
|
1086 | extensions to the floating point numbers of your platform, such as |
|
|
1087 | infinities or NaN's - these cannot be represented in JSON, and it is an |
|
|
1088 | error to pass those in. |
823 | |
1089 | |
824 | =back |
1090 | =back |
825 | |
1091 | |
826 | |
1092 | |
827 | =head1 ENCODING/CODESET FLAG NOTES |
1093 | =head1 ENCODING/CODESET FLAG NOTES |
828 | |
1094 | |
829 | The interested reader might have seen a number of flags that signify |
1095 | The interested reader might have seen a number of flags that signify |
830 | encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be |
1096 | encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be |
831 | some confusion on what these do, so here is a short comparison: |
1097 | some confusion on what these do, so here is a short comparison: |
832 | |
1098 | |
833 | C<utf8> controls wether the JSON text created by C<encode> (and expected |
1099 | C<utf8> controls whether the JSON text created by C<encode> (and expected |
834 | by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only |
1100 | by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only |
835 | control wether C<encode> escapes character values outside their respective |
1101 | control whether C<encode> escapes character values outside their respective |
836 | codeset range. Neither of these flags conflict with each other, although |
1102 | codeset range. Neither of these flags conflict with each other, although |
837 | some combinations make less sense than others. |
1103 | some combinations make less sense than others. |
838 | |
1104 | |
839 | Care has been taken to make all flags symmetrical with respect to |
1105 | Care has been taken to make all flags symmetrical with respect to |
840 | C<encode> and C<decode>, that is, texts encoded with any combination of |
1106 | C<encode> and C<decode>, that is, texts encoded with any combination of |
… | |
… | |
854 | =item C<utf8> flag disabled |
1120 | =item C<utf8> flag disabled |
855 | |
1121 | |
856 | When C<utf8> is disabled (the default), then C<encode>/C<decode> generate |
1122 | When C<utf8> is disabled (the default), then C<encode>/C<decode> generate |
857 | and expect Unicode strings, that is, characters with high ordinal Unicode |
1123 | and expect Unicode strings, that is, characters with high ordinal Unicode |
858 | values (> 255) will be encoded as such characters, and likewise such |
1124 | values (> 255) will be encoded as such characters, and likewise such |
859 | characters are decoded as-is, no canges to them will be done, except |
1125 | characters are decoded as-is, no changes to them will be done, except |
860 | "(re-)interpreting" them as Unicode codepoints or Unicode characters, |
1126 | "(re-)interpreting" them as Unicode codepoints or Unicode characters, |
861 | respectively (to Perl, these are the same thing in strings unless you do |
1127 | respectively (to Perl, these are the same thing in strings unless you do |
862 | funny/weird/dumb stuff). |
1128 | funny/weird/dumb stuff). |
863 | |
1129 | |
864 | This is useful when you want to do the encoding yourself (e.g. when you |
1130 | This is useful when you want to do the encoding yourself (e.g. when you |
… | |
… | |
920 | proper subset of most 8-bit and multibyte encodings in use in the world. |
1186 | proper subset of most 8-bit and multibyte encodings in use in the world. |
921 | |
1187 | |
922 | =back |
1188 | =back |
923 | |
1189 | |
924 | |
1190 | |
925 | =head1 COMPARISON |
1191 | =head2 JSON and ECMAscript |
926 | |
1192 | |
927 | As already mentioned, this module was created because none of the existing |
1193 | JSON syntax is based on how literals are represented in javascript (the |
928 | JSON modules could be made to work correctly. First I will describe the |
1194 | not-standardised predecessor of ECMAscript) which is presumably why it is |
929 | problems (or pleasures) I encountered with various existing JSON modules, |
1195 | called "JavaScript Object Notation". |
930 | followed by some benchmark values. JSON::XS was designed not to suffer |
|
|
931 | from any of these problems or limitations. |
|
|
932 | |
1196 | |
933 | =over 4 |
1197 | However, JSON is not a subset (and also not a superset of course) of |
|
|
1198 | ECMAscript (the standard) or javascript (whatever browsers actually |
|
|
1199 | implement). |
934 | |
1200 | |
935 | =item JSON 2.xx |
1201 | If you want to use javascript's C<eval> function to "parse" JSON, you |
|
|
1202 | might run into parse errors for valid JSON texts, or the resulting data |
|
|
1203 | structure might not be queryable: |
936 | |
1204 | |
937 | A marvellous piece of engineering, this module either uses JSON::XS |
1205 | One of the problems is that U+2028 and U+2029 are valid characters inside |
938 | directly when available (so will be 100% compatible with it, including |
1206 | JSON strings, but are not allowed in ECMAscript string literals, so the |
939 | speed), or it uses JSON::PP, which is basically JSON::XS translated to |
1207 | following Perl fragment will not output something that can be guaranteed |
940 | Pure Perl, which should be 100% compatible with JSON::XS, just a bit |
1208 | to be parsable by javascript's C<eval>: |
941 | slower. |
|
|
942 | |
1209 | |
943 | You cannot really lose by using this module, especially as it tries very |
1210 | use JSON::XS; |
944 | hard to work even with ancient Perl versions, while JSON::XS does not. |
|
|
945 | |
1211 | |
946 | =item JSON 1.07 |
1212 | print encode_json [chr 0x2028]; |
947 | |
1213 | |
948 | Slow (but very portable, as it is written in pure Perl). |
1214 | The right fix for this is to use a proper JSON parser in your javascript |
|
|
1215 | programs, and not rely on C<eval> (see for example Douglas Crockford's |
|
|
1216 | F<json2.js> parser). |
949 | |
1217 | |
950 | Undocumented/buggy Unicode handling (how JSON handles Unicode values is |
1218 | If this is not an option, you can, as a stop-gap measure, simply encode to |
951 | undocumented. One can get far by feeding it Unicode strings and doing |
1219 | ASCII-only JSON: |
952 | en-/decoding oneself, but Unicode escapes are not working properly). |
|
|
953 | |
1220 | |
954 | No round-tripping (strings get clobbered if they look like numbers, e.g. |
1221 | use JSON::XS; |
955 | the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will |
|
|
956 | decode into the number 2. |
|
|
957 | |
1222 | |
958 | =item JSON::PC 0.01 |
1223 | print JSON::XS->new->ascii->encode ([chr 0x2028]); |
959 | |
1224 | |
960 | Very fast. |
1225 | Note that this will enlarge the resulting JSON text quite a bit if you |
|
|
1226 | have many non-ASCII characters. You might be tempted to run some regexes |
|
|
1227 | to only escape U+2028 and U+2029, e.g.: |
961 | |
1228 | |
962 | Undocumented/buggy Unicode handling. |
1229 | # DO NOT USE THIS! |
|
|
1230 | my $json = JSON::XS->new->utf8->encode ([chr 0x2028]); |
|
|
1231 | $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028 |
|
|
1232 | $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029 |
|
|
1233 | print $json; |
963 | |
1234 | |
964 | No round-tripping. |
1235 | Note that I<this is a bad idea>: the above only works for U+2028 and |
|
|
1236 | U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing |
|
|
1237 | javascript implementations, however, have issues with other characters as |
|
|
1238 | well - using C<eval> naively simply I<will> cause problems. |
965 | |
1239 | |
966 | Has problems handling many Perl values (e.g. regex results and other magic |
1240 | Another problem is that some javascript implementations reserve |
967 | values will make it croak). |
1241 | some property names for their own purposes (which probably makes |
|
|
1242 | them non-ECMAscript-compliant). For example, Iceweasel reserves the |
|
|
1243 | C<__proto__> property name for its own purposes. |
968 | |
1244 | |
969 | Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> |
1245 | If that is a problem, you could parse try to filter the resulting JSON |
970 | which is not a valid JSON text. |
1246 | output for these property strings, e.g.: |
971 | |
1247 | |
972 | Unmaintained (maintainer unresponsive for many months, bugs are not |
1248 | $json =~ s/"__proto__"\s*:/"__proto__renamed":/g; |
973 | getting fixed). |
|
|
974 | |
1249 | |
975 | =item JSON::Syck 0.21 |
1250 | This works because C<__proto__> is not valid outside of strings, so every |
|
|
1251 | occurrence of C<"__proto__"\s*:> must be a string used as property name. |
976 | |
1252 | |
977 | Very buggy (often crashes). |
1253 | If you know of other incompatibilities, please let me know. |
978 | |
|
|
979 | Very inflexible (no human-readable format supported, format pretty much |
|
|
980 | undocumented. I need at least a format for easy reading by humans and a |
|
|
981 | single-line compact format for use in a protocol, and preferably a way to |
|
|
982 | generate ASCII-only JSON texts). |
|
|
983 | |
|
|
984 | Completely broken (and confusingly documented) Unicode handling (Unicode |
|
|
985 | escapes are not working properly, you need to set ImplicitUnicode to |
|
|
986 | I<different> values on en- and decoding to get symmetric behaviour). |
|
|
987 | |
|
|
988 | No round-tripping (simple cases work, but this depends on whether the scalar |
|
|
989 | value was used in a numeric context or not). |
|
|
990 | |
|
|
991 | Dumping hashes may skip hash values depending on iterator state. |
|
|
992 | |
|
|
993 | Unmaintained (maintainer unresponsive for many months, bugs are not |
|
|
994 | getting fixed). |
|
|
995 | |
|
|
996 | Does not check input for validity (i.e. will accept non-JSON input and |
|
|
997 | return "something" instead of raising an exception. This is a security |
|
|
998 | issue: imagine two banks transferring money between each other using |
|
|
999 | JSON. One bank might parse a given non-JSON request and deduct money, |
|
|
1000 | while the other might reject the transaction with a syntax error. While a |
|
|
1001 | good protocol will at least recover, that is extra unnecessary work and |
|
|
1002 | the transaction will still not succeed). |
|
|
1003 | |
|
|
1004 | =item JSON::DWIW 0.04 |
|
|
1005 | |
|
|
1006 | Very fast. Very natural. Very nice. |
|
|
1007 | |
|
|
1008 | Undocumented Unicode handling (but the best of the pack. Unicode escapes |
|
|
1009 | still don't get parsed properly). |
|
|
1010 | |
|
|
1011 | Very inflexible. |
|
|
1012 | |
|
|
1013 | No round-tripping. |
|
|
1014 | |
|
|
1015 | Does not generate valid JSON texts (key strings are often unquoted, empty keys |
|
|
1016 | result in nothing being output) |
|
|
1017 | |
|
|
1018 | Does not check input for validity. |
|
|
1019 | |
|
|
1020 | =back |
|
|
1021 | |
1254 | |
1022 | |
1255 | |
1023 | =head2 JSON and YAML |
1256 | =head2 JSON and YAML |
1024 | |
1257 | |
1025 | You often hear that JSON is a subset of YAML. This is, however, a mass |
1258 | You often hear that JSON is a subset of YAML. This is, however, a mass |
1026 | hysteria(*) and very far from the truth. In general, there is no way to |
1259 | hysteria(*) and very far from the truth (as of the time of this writing), |
|
|
1260 | so let me state it clearly: I<in general, there is no way to configure |
1027 | configure JSON::XS to output a data structure as valid YAML that works for |
1261 | JSON::XS to output a data structure as valid YAML> that works in all |
1028 | all cases. |
1262 | cases. |
1029 | |
1263 | |
1030 | If you really must use JSON::XS to generate YAML, you should use this |
1264 | If you really must use JSON::XS to generate YAML, you should use this |
1031 | algorithm (subject to change in future versions): |
1265 | algorithm (subject to change in future versions): |
1032 | |
1266 | |
1033 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
1267 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
1034 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
1268 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
1035 | |
1269 | |
1036 | This will I<usually> generate JSON texts that also parse as valid |
1270 | This will I<usually> generate JSON texts that also parse as valid |
1037 | YAML. Please note that YAML has hardcoded limits on (simple) object key |
1271 | YAML. Please note that YAML has hardcoded limits on (simple) object key |
1038 | lengths that JSON doesn't have and also has different and incompatible |
1272 | 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 |
1273 | unicode character escape syntax, so you should make sure that your hash |
1040 | noticeably shorter than the 1024 "stream characters" YAML allows and that |
1274 | keys are noticeably shorter than the 1024 "stream characters" YAML allows |
1041 | you do not have codepoints with values outside the Unicode BMP (basic |
1275 | and that you do not have characters with codepoint values outside the |
1042 | multilingual page). YAML also does not allow C<\/> sequences in strings |
1276 | Unicode BMP (basic multilingual page). YAML also does not allow C<\/> |
1043 | (which JSON::XS does not I<currently> generate). |
1277 | sequences in strings (which JSON::XS does not I<currently> generate, but |
|
|
1278 | other JSON generators might). |
1044 | |
1279 | |
1045 | There might be other incompatibilities that I am not aware of (or the YAML |
1280 | 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 |
1281 | specification has been changed yet again - it does so quite often). In |
1047 | general you should not try to generate YAML with a JSON generator or vice |
1282 | general you should not try to generate YAML with a JSON generator or vice |
1048 | versa, or try to parse JSON with a YAML parser or vice versa: chances are |
1283 | versa, or try to parse JSON with a YAML parser or vice versa: chances are |
… | |
… | |
1051 | |
1286 | |
1052 | =over 4 |
1287 | =over 4 |
1053 | |
1288 | |
1054 | =item (*) |
1289 | =item (*) |
1055 | |
1290 | |
1056 | This is spread actively by the YAML team, however. For many years now they |
1291 | I have been pressured multiple times by Brian Ingerson (one of the |
1057 | claim YAML were a superset of JSON, even when proven otherwise. |
1292 | authors of the YAML specification) to remove this paragraph, despite him |
|
|
1293 | acknowledging that the actual incompatibilities exist. As I was personally |
|
|
1294 | bitten by this "JSON is YAML" lie, I refused and said I will continue to |
|
|
1295 | educate people about these issues, so others do not run into the same |
|
|
1296 | problem again and again. After this, Brian called me a (quote)I<complete |
|
|
1297 | and worthless idiot>(unquote). |
1058 | |
1298 | |
1059 | Even the author of this manpage was at some point accused of providing |
1299 | In my opinion, instead of pressuring and insulting people who actually |
1060 | "incorrect" information, despite the evidence presented (claims ranged |
1300 | clarify issues with YAML and the wrong statements of some of its |
1061 | from "your documentation contains inaccurate and negative statements about |
1301 | proponents, I would kindly suggest reading the JSON spec (which is not |
1062 | YAML" (the only negative comment is this footnote, and it didn't exist |
1302 | that difficult or long) and finally make YAML compatible to it, and |
1063 | back then; the question on which claims were inaccurate was never answered |
1303 | educating users about the changes, instead of spreading lies about the |
1064 | etc.) to "the YAML spec is not up-to-date" (the *real* and supposedly |
1304 | real compatibility for many I<years> and trying to silence people who |
1065 | JSON-compatible spec is apparently not currently publicly available) |
1305 | point out that it isn't true. |
1066 | to actual requests to replace this section by *incorrect* information, |
|
|
1067 | suppressing information about the real problem). |
|
|
1068 | |
1306 | |
1069 | So whenever you are told that YAML was a superset of JSON, first check |
1307 | Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even |
1070 | wether it is really true (it might be when you check it, but it certainly |
1308 | though the incompatibilities have been documented (and are known to Brian) |
1071 | was not true when this was written). I would much prefer if the YAML team |
1309 | for many years and the spec makes explicit claims that YAML is a superset |
1072 | would spent their time on actually making JSON compatibility a truth |
1310 | of JSON. It would be so easy to fix, but apparently, bullying people and |
1073 | (JSON, after all, has a very small and simple specification) instead of |
1311 | corrupting userdata is so much easier. |
1074 | trying to lobby/force people into reporting untruths. |
|
|
1075 | |
1312 | |
1076 | =back |
1313 | =back |
1077 | |
1314 | |
1078 | |
1315 | |
1079 | =head2 SPEED |
1316 | =head2 SPEED |
… | |
… | |
1083 | in the JSON::XS distribution, to make it easy to compare on your own |
1320 | in the JSON::XS distribution, to make it easy to compare on your own |
1084 | system. |
1321 | system. |
1085 | |
1322 | |
1086 | First comes a comparison between various modules using |
1323 | First comes a comparison between various modules using |
1087 | a very short single-line JSON string (also available at |
1324 | a very short single-line JSON string (also available at |
1088 | L<http://dist.schmorp.de/misc/json/long.json>). |
1325 | L<http://dist.schmorp.de/misc/json/short.json>). |
1089 | |
1326 | |
1090 | {"method": "handleMessage", "params": ["user1", "we were just talking"], \ |
1327 | {"method": "handleMessage", "params": ["user1", |
1091 | "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} |
1328 | "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7, |
|
|
1329 | 1, 0]} |
1092 | |
1330 | |
1093 | It shows the number of encodes/decodes per second (JSON::XS uses |
1331 | It shows the number of encodes/decodes per second (JSON::XS uses |
1094 | the functional interface, while JSON::XS/2 uses the OO interface |
1332 | the functional interface, while JSON::XS/2 uses the OO interface |
1095 | with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables |
1333 | with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables |
1096 | shrink). Higher is better: |
1334 | shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ |
|
|
1335 | uses the from_json method). Higher is better: |
1097 | |
1336 | |
1098 | module | encode | decode | |
1337 | module | encode | decode | |
1099 | -----------|------------|------------| |
1338 | --------------|------------|------------| |
1100 | JSON 1.x | 4990.842 | 4088.813 | |
1339 | JSON::DWIW/DS | 86302.551 | 102300.098 | |
1101 | JSON::DWIW | 51653.990 | 71575.154 | |
1340 | JSON::DWIW/FJ | 86302.551 | 75983.768 | |
1102 | JSON::PC | 65948.176 | 74631.744 | |
1341 | JSON::PP | 15827.562 | 6638.658 | |
1103 | JSON::PP | 8931.652 | 3817.168 | |
1342 | JSON::Syck | 63358.066 | 47662.545 | |
1104 | JSON::Syck | 24877.248 | 27776.848 | |
1343 | JSON::XS | 511500.488 | 511500.488 | |
1105 | JSON::XS | 388361.481 | 227951.304 | |
1344 | JSON::XS/2 | 291271.111 | 388361.481 | |
1106 | JSON::XS/2 | 227951.304 | 218453.333 | |
1345 | JSON::XS/3 | 361577.931 | 361577.931 | |
1107 | JSON::XS/3 | 338250.323 | 218453.333 | |
1346 | Storable | 66788.280 | 265462.278 | |
1108 | Storable | 16500.016 | 135300.129 | |
|
|
1109 | -----------+------------+------------+ |
1347 | --------------+------------+------------+ |
1110 | |
1348 | |
1111 | That is, JSON::XS is about five times faster than JSON::DWIW on encoding, |
1349 | That is, JSON::XS is almost six times faster than JSON::DWIW on encoding, |
1112 | about three times faster on decoding, and over forty times faster |
1350 | about five times faster on decoding, and over thirty to seventy times |
1113 | than JSON, even with pretty-printing and key sorting. It also compares |
1351 | faster than JSON's pure perl implementation. It also compares favourably |
1114 | favourably to Storable for small amounts of data. |
1352 | to Storable for small amounts of data. |
1115 | |
1353 | |
1116 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
1354 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
1117 | search API (L>http://dist.schmorp.de/misc/json/long.json>). |
1355 | search API (L<http://dist.schmorp.de/misc/json/long.json>). |
1118 | |
1356 | |
1119 | module | encode | decode | |
1357 | module | encode | decode | |
1120 | -----------|------------|------------| |
1358 | --------------|------------|------------| |
1121 | JSON 1.x | 55.260 | 34.971 | |
1359 | JSON::DWIW/DS | 1647.927 | 2673.916 | |
1122 | JSON::DWIW | 825.228 | 1082.513 | |
1360 | JSON::DWIW/FJ | 1630.249 | 2596.128 | |
1123 | JSON::PC | 3571.444 | 2394.829 | |
|
|
1124 | JSON::PP | 210.987 | 32.574 | |
1361 | JSON::PP | 400.640 | 62.311 | |
1125 | JSON::Syck | 552.551 | 787.544 | |
1362 | JSON::Syck | 1481.040 | 1524.869 | |
1126 | JSON::XS | 5780.463 | 4854.519 | |
1363 | JSON::XS | 20661.596 | 9541.183 | |
1127 | JSON::XS/2 | 3869.998 | 4798.975 | |
1364 | JSON::XS/2 | 10683.403 | 9416.938 | |
1128 | JSON::XS/3 | 5862.880 | 4798.975 | |
1365 | JSON::XS/3 | 20661.596 | 9400.054 | |
1129 | Storable | 4445.002 | 5235.027 | |
1366 | Storable | 19765.806 | 10000.725 | |
1130 | -----------+------------+------------+ |
1367 | --------------+------------+------------+ |
1131 | |
1368 | |
1132 | Again, JSON::XS leads by far (except for Storable which non-surprisingly |
1369 | Again, JSON::XS leads by far (except for Storable which non-surprisingly |
1133 | decodes faster). |
1370 | decodes a bit faster). |
1134 | |
1371 | |
1135 | On large strings containing lots of high Unicode characters, some modules |
1372 | On large strings containing lots of high Unicode characters, some modules |
1136 | (such as JSON::PC) seem to decode faster than JSON::XS, but the result |
1373 | (such as JSON::PC) seem to decode faster than JSON::XS, but the result |
1137 | will be broken due to missing (or wrong) Unicode handling. Others refuse |
1374 | will be broken due to missing (or wrong) Unicode handling. Others refuse |
1138 | to decode or encode properly, so it was impossible to prepare a fair |
1375 | to decode or encode properly, so it was impossible to prepare a fair |
… | |
… | |
1174 | information you might want to make sure that exceptions thrown by JSON::XS |
1411 | information you might want to make sure that exceptions thrown by JSON::XS |
1175 | will not end up in front of untrusted eyes. |
1412 | will not end up in front of untrusted eyes. |
1176 | |
1413 | |
1177 | If you are using JSON::XS to return packets to consumption |
1414 | If you are using JSON::XS to return packets to consumption |
1178 | by JavaScript scripts in a browser you should have a look at |
1415 | by JavaScript scripts in a browser you should have a look at |
1179 | L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether |
1416 | L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to |
1180 | you are vulnerable to some common attack vectors (which really are browser |
1417 | see whether you are vulnerable to some common attack vectors (which really |
1181 | design bugs, but it is still you who will have to deal with it, as major |
1418 | are browser design bugs, but it is still you who will have to deal with |
1182 | browser developers care only for features, not about getting security |
1419 | it, as major browser developers care only for features, not about getting |
1183 | right). |
1420 | security right). |
1184 | |
1421 | |
1185 | |
1422 | |
1186 | =head1 THREADS |
1423 | =head1 THREADS |
1187 | |
1424 | |
1188 | This module is I<not> guaranteed to be thread safe and there are no |
1425 | This module is I<not> guaranteed to be thread safe and there are no |
1189 | plans to change this until Perl gets thread support (as opposed to the |
1426 | plans to change this until Perl gets thread support (as opposed to the |
1190 | horribly slow so-called "threads" which are simply slow and bloated |
1427 | horribly slow so-called "threads" which are simply slow and bloated |
1191 | process simulations - use fork, its I<much> faster, cheaper, better). |
1428 | process simulations - use fork, it's I<much> faster, cheaper, better). |
1192 | |
1429 | |
1193 | (It might actually work, but you have been warned). |
1430 | (It might actually work, but you have been warned). |
1194 | |
1431 | |
1195 | |
1432 | |
|
|
1433 | =head1 THE PERILS OF SETLOCALE |
|
|
1434 | |
|
|
1435 | Sometimes people avoid the Perl locale support and directly call the |
|
|
1436 | system's setlocale function with C<LC_ALL>. |
|
|
1437 | |
|
|
1438 | This breaks both perl and modules such as JSON::XS, as stringification of |
|
|
1439 | numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might |
|
|
1440 | print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on |
|
|
1441 | perl to stringify numbers). |
|
|
1442 | |
|
|
1443 | The solution is simple: don't call C<setlocale>, or use it for only those |
|
|
1444 | categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>. |
|
|
1445 | |
|
|
1446 | If you need C<LC_NUMERIC>, you should enable it only around the code that |
|
|
1447 | actually needs it (avoiding stringification of numbers), and restore it |
|
|
1448 | afterwards. |
|
|
1449 | |
|
|
1450 | |
1196 | =head1 BUGS |
1451 | =head1 BUGS |
1197 | |
1452 | |
1198 | While the goal of this module is to be correct, that unfortunately does |
1453 | While the goal of this module is to be correct, that unfortunately does |
1199 | not mean its bug-free, only that I think its design is bug-free. It is |
1454 | not mean it's bug-free, only that I think its design is bug-free. If you |
1200 | still relatively early in its development. If you keep reporting bugs they |
1455 | keep reporting bugs they will be fixed swiftly, though. |
1201 | will be fixed swiftly, though. |
|
|
1202 | |
1456 | |
1203 | Please refrain from using rt.cpan.org or any other bug reporting |
1457 | Please refrain from using rt.cpan.org or any other bug reporting |
1204 | service. I put the contact address into my modules for a reason. |
1458 | service. I put the contact address into my modules for a reason. |
1205 | |
1459 | |
1206 | =cut |
1460 | =cut |
… | |
… | |
1226 | "--" => sub { $_[0] = ${$_[0]} - 1 }, |
1480 | "--" => sub { $_[0] = ${$_[0]} - 1 }, |
1227 | fallback => 1; |
1481 | fallback => 1; |
1228 | |
1482 | |
1229 | 1; |
1483 | 1; |
1230 | |
1484 | |
|
|
1485 | =head1 SEE ALSO |
|
|
1486 | |
|
|
1487 | The F<json_xs> command line utility for quick experiments. |
|
|
1488 | |
1231 | =head1 AUTHOR |
1489 | =head1 AUTHOR |
1232 | |
1490 | |
1233 | Marc Lehmann <schmorp@schmorp.de> |
1491 | Marc Lehmann <schmorp@schmorp.de> |
1234 | http://home.schmorp.de/ |
1492 | http://home.schmorp.de/ |
1235 | |
1493 | |