1 | =head1 NAME |
1 | =head1 NAME |
2 | |
2 | |
3 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
3 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
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4 | |
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5 | =encoding utf-8 |
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 |
6 | (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) |
8 | (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) |
7 | |
9 | |
8 | =head1 SYNOPSIS |
10 | =head1 SYNOPSIS |
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35 | 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 |
36 | 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. |
37 | |
39 | |
38 | 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 |
39 | 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 |
40 | overriden) with no overhead due to emulation (by inheritign constructor |
42 | overridden) with no overhead due to emulation (by inheriting constructor |
41 | 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 |
42 | 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 |
43 | 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 |
44 | require a C compiler when that is a problem. |
46 | require a C compiler when that is a problem. |
45 | |
47 | |
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47 | 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 |
48 | 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 |
49 | their maintainers are unresponsive, gone missing, or not listening to bug |
51 | their maintainers are unresponsive, gone missing, or not listening to bug |
50 | reports for other reasons. |
52 | reports for other reasons. |
51 | |
53 | |
52 | See COMPARISON, below, for a comparison to some other JSON modules. |
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53 | |
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54 | 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 |
55 | vice versa. |
55 | vice versa. |
56 | |
56 | |
57 | =head2 FEATURES |
57 | =head2 FEATURES |
58 | |
58 | |
59 | =over 4 |
59 | =over 4 |
60 | |
60 | |
61 | =item * correct Unicode handling |
61 | =item * correct Unicode handling |
62 | |
62 | |
63 | This module knows how to handle Unicode, and even documents how and when |
63 | This module knows how to handle Unicode, documents how and when it does |
64 | it does so. |
64 | so, and even documents what "correct" means. |
65 | |
65 | |
66 | =item * round-trip integrity |
66 | =item * round-trip integrity |
67 | |
67 | |
68 | When you serialise a perl data structure using only datatypes supported |
68 | When you serialise a perl data structure using only data types supported |
69 | 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 |
70 | (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 |
71 | like a number). |
71 | it looks like a number). There I<are> minor exceptions to this, read the |
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72 | MAPPING section below to learn about those. |
72 | |
73 | |
73 | =item * strict checking of JSON correctness |
74 | =item * strict checking of JSON correctness |
74 | |
75 | |
75 | 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, |
76 | 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 |
77 | feature). |
78 | feature). |
78 | |
79 | |
79 | =item * fast |
80 | =item * fast |
80 | |
81 | |
81 | Compared to other JSON modules, this module compares favourably in terms |
82 | Compared to other JSON modules and other serialisers such as Storable, |
82 | of speed, too. |
83 | this module usually compares favourably in terms of speed, too. |
83 | |
84 | |
84 | =item * simple to use |
85 | =item * simple to use |
85 | |
86 | |
86 | This module has both a simple functional interface as well as an OO |
87 | This module has both a simple functional interface as well as an object |
87 | interface. |
88 | oriented interface. |
88 | |
89 | |
89 | =item * reasonably versatile output formats |
90 | =item * reasonably versatile output formats |
90 | |
91 | |
91 | You can choose between the most compact guaranteed single-line format |
92 | You can choose between the most compact guaranteed-single-line format |
92 | possible (nice for simple line-based protocols), a pure-ascii format |
93 | possible (nice for simple line-based protocols), a pure-ASCII format |
93 | (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 |
94 | 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 |
95 | 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. |
96 | |
97 | |
97 | =back |
98 | =back |
98 | |
99 | |
99 | =cut |
100 | =cut |
100 | |
101 | |
101 | package JSON::XS; |
102 | package JSON::XS; |
102 | |
103 | |
103 | use strict; |
104 | use common::sense; |
104 | |
105 | |
105 | our $VERSION = '2.01'; |
106 | our $VERSION = 3.01; |
106 | our @ISA = qw(Exporter); |
107 | our @ISA = qw(Exporter); |
107 | |
108 | |
108 | our @EXPORT = qw(encode_json decode_json to_json from_json); |
109 | our @EXPORT = qw(encode_json decode_json); |
109 | |
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110 | sub to_json($) { |
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111 | require Carp; |
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112 | 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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113 | } |
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114 | |
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115 | sub from_json($) { |
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116 | require Carp; |
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117 | 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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118 | } |
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119 | |
110 | |
120 | use Exporter; |
111 | use Exporter; |
121 | use XSLoader; |
112 | use XSLoader; |
122 | |
113 | |
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114 | use Types::Serialiser (); |
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115 | |
123 | =head1 FUNCTIONAL INTERFACE |
116 | =head1 FUNCTIONAL INTERFACE |
124 | |
117 | |
125 | The following convenience methods are provided by this module. They are |
118 | The following convenience methods are provided by this module. They are |
126 | exported by default: |
119 | exported by default: |
127 | |
120 | |
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134 | |
127 | |
135 | This function call is functionally identical to: |
128 | This function call is functionally identical to: |
136 | |
129 | |
137 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
130 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
138 | |
131 | |
139 | except being faster. |
132 | Except being faster. |
140 | |
133 | |
141 | =item $perl_scalar = decode_json $json_text |
134 | =item $perl_scalar = decode_json $json_text |
142 | |
135 | |
143 | The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries |
136 | The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries |
144 | to parse that as an UTF-8 encoded JSON text, returning the resulting |
137 | to parse that as an UTF-8 encoded JSON text, returning the resulting |
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146 | |
139 | |
147 | This function call is functionally identical to: |
140 | This function call is functionally identical to: |
148 | |
141 | |
149 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
142 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
150 | |
143 | |
151 | except being faster. |
144 | Except being faster. |
152 | |
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153 | =item $is_boolean = JSON::XS::is_bool $scalar |
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154 | |
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155 | Returns true if the passed scalar represents either JSON::XS::true or |
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156 | JSON::XS::false, two constants that act like C<1> and C<0>, respectively |
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157 | and are used to represent JSON C<true> and C<false> values in Perl. |
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158 | |
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159 | See MAPPING, below, for more information on how JSON values are mapped to |
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160 | Perl. |
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161 | |
145 | |
162 | =back |
146 | =back |
163 | |
147 | |
164 | |
148 | |
165 | =head1 A FEW NOTES ON UNICODE AND PERL |
149 | =head1 A FEW NOTES ON UNICODE AND PERL |
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174 | This enables you to store Unicode characters as single characters in a |
158 | This enables you to store Unicode characters as single characters in a |
175 | Perl string - very natural. |
159 | Perl string - very natural. |
176 | |
160 | |
177 | =item 2. Perl does I<not> associate an encoding with your strings. |
161 | =item 2. Perl does I<not> associate an encoding with your strings. |
178 | |
162 | |
179 | Unless you force it to, e.g. when matching it against a regex, or printing |
163 | ... until you force it to, e.g. when matching it against a regex, or |
180 | the scalar to a file, in which case Perl either interprets your string as |
164 | printing the scalar to a file, in which case Perl either interprets your |
181 | locale-encoded text, octets/binary, or as Unicode, depending on various |
165 | string as locale-encoded text, octets/binary, or as Unicode, depending |
182 | settings. In no case is an encoding stored together with your data, it is |
166 | on various settings. In no case is an encoding stored together with your |
183 | I<use> that decides encoding, not any magical metadata. |
167 | data, it is I<use> that decides encoding, not any magical meta data. |
184 | |
168 | |
185 | =item 3. The internal utf-8 flag has no meaning with regards to the |
169 | =item 3. The internal utf-8 flag has no meaning with regards to the |
186 | encoding of your string. |
170 | encoding of your string. |
187 | |
171 | |
188 | Just ignore that flag unless you debug a Perl bug, a module written in |
172 | Just ignore that flag unless you debug a Perl bug, a module written in |
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194 | |
178 | |
195 | If you didn't know about that flag, just the better, pretend it doesn't |
179 | If you didn't know about that flag, just the better, pretend it doesn't |
196 | exist. |
180 | exist. |
197 | |
181 | |
198 | =item 4. A "Unicode String" is simply a string where each character can be |
182 | =item 4. A "Unicode String" is simply a string where each character can be |
199 | validly interpreted as a Unicode codepoint. |
183 | validly interpreted as a Unicode code point. |
200 | |
184 | |
201 | If you have UTF-8 encoded data, it is no longer a Unicode string, but a |
185 | If you have UTF-8 encoded data, it is no longer a Unicode string, but a |
202 | Unicode string encoded in UTF-8, giving you a binary string. |
186 | Unicode string encoded in UTF-8, giving you a binary string. |
203 | |
187 | |
204 | =item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string. |
188 | =item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string. |
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242 | |
226 | |
243 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
227 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
244 | characters unless required by the JSON syntax or other flags. This results |
228 | characters unless required by the JSON syntax or other flags. This results |
245 | in a faster and more compact format. |
229 | in a faster and more compact format. |
246 | |
230 | |
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231 | See also the section I<ENCODING/CODESET FLAG NOTES> later in this |
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232 | document. |
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233 | |
247 | The main use for this flag is to produce JSON texts that can be |
234 | The main use for this flag is to produce JSON texts that can be |
248 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
235 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
249 | contain any 8 bit characters. |
236 | contain any 8 bit characters. |
250 | |
237 | |
251 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
238 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
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262 | will not be affected in any way by this flag, as C<decode> by default |
249 | will not be affected in any way by this flag, as C<decode> by default |
263 | expects Unicode, which is a strict superset of latin1. |
250 | expects Unicode, which is a strict superset of latin1. |
264 | |
251 | |
265 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
252 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
266 | characters unless required by the JSON syntax or other flags. |
253 | characters unless required by the JSON syntax or other flags. |
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254 | |
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255 | See also the section I<ENCODING/CODESET FLAG NOTES> later in this |
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256 | document. |
267 | |
257 | |
268 | The main use for this flag is efficiently encoding binary data as JSON |
258 | The main use for this flag is efficiently encoding binary data as JSON |
269 | text, as most octets will not be escaped, resulting in a smaller encoded |
259 | text, as most octets will not be escaped, resulting in a smaller encoded |
270 | size. The disadvantage is that the resulting JSON text is encoded |
260 | size. The disadvantage is that the resulting JSON text is encoded |
271 | in latin1 (and must correctly be treated as such when storing and |
261 | in latin1 (and must correctly be treated as such when storing and |
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290 | |
280 | |
291 | If C<$enable> is false, then the C<encode> method will return the JSON |
281 | If C<$enable> is false, then the C<encode> method will return the JSON |
292 | string as a (non-encoded) Unicode string, while C<decode> expects thus a |
282 | string as a (non-encoded) Unicode string, while C<decode> expects thus a |
293 | Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs |
283 | Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs |
294 | to be done yourself, e.g. using the Encode module. |
284 | to be done yourself, e.g. using the Encode module. |
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285 | |
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286 | See also the section I<ENCODING/CODESET FLAG NOTES> later in this |
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287 | document. |
295 | |
288 | |
296 | Example, output UTF-16BE-encoded JSON: |
289 | Example, output UTF-16BE-encoded JSON: |
297 | |
290 | |
298 | use Encode; |
291 | use Encode; |
299 | $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
292 | $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
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422 | If C<$enable> is true (or missing), then the C<encode> method will output JSON objects |
415 | If C<$enable> is true (or missing), then the C<encode> method will output JSON objects |
423 | by sorting their keys. This is adding a comparatively high overhead. |
416 | by sorting their keys. This is adding a comparatively high overhead. |
424 | |
417 | |
425 | If C<$enable> is false, then the C<encode> method will output key-value |
418 | If C<$enable> is false, then the C<encode> method will output key-value |
426 | pairs in the order Perl stores them (which will likely change between runs |
419 | pairs in the order Perl stores them (which will likely change between runs |
427 | of the same script). |
420 | of the same script, and can change even within the same run from 5.18 |
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421 | onwards). |
428 | |
422 | |
429 | This option is useful if you want the same data structure to be encoded as |
423 | This option is useful if you want the same data structure to be encoded as |
430 | the same JSON text (given the same overall settings). If it is disabled, |
424 | the same JSON text (given the same overall settings). If it is disabled, |
431 | the same hash might be encoded differently even if contains the same data, |
425 | the same hash might be encoded differently even if contains the same data, |
432 | as key-value pairs have no inherent ordering in Perl. |
426 | as key-value pairs have no inherent ordering in Perl. |
433 | |
427 | |
434 | This setting has no effect when decoding JSON texts. |
428 | This setting has no effect when decoding JSON texts. |
435 | |
429 | |
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430 | This setting has currently no effect on tied hashes. |
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431 | |
436 | =item $json = $json->allow_nonref ([$enable]) |
432 | =item $json = $json->allow_nonref ([$enable]) |
437 | |
433 | |
438 | =item $enabled = $json->get_allow_nonref |
434 | =item $enabled = $json->get_allow_nonref |
439 | |
435 | |
440 | If C<$enable> is true (or missing), then the C<encode> method can convert a |
436 | If C<$enable> is true (or missing), then the C<encode> method can convert a |
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451 | resulting in an invalid JSON text: |
447 | resulting in an invalid JSON text: |
452 | |
448 | |
453 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
449 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
454 | => "Hello, World!" |
450 | => "Hello, World!" |
455 | |
451 | |
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452 | =item $json = $json->allow_unknown ([$enable]) |
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453 | |
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454 | =item $enabled = $json->get_allow_unknown |
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455 | |
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456 | If C<$enable> is true (or missing), then C<encode> will I<not> throw an |
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457 | exception when it encounters values it cannot represent in JSON (for |
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458 | example, filehandles) but instead will encode a JSON C<null> value. Note |
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459 | that blessed objects are not included here and are handled separately by |
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460 | c<allow_nonref>. |
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461 | |
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462 | If C<$enable> is false (the default), then C<encode> will throw an |
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463 | exception when it encounters anything it cannot encode as JSON. |
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464 | |
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465 | This option does not affect C<decode> in any way, and it is recommended to |
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466 | leave it off unless you know your communications partner. |
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467 | |
456 | =item $json = $json->allow_blessed ([$enable]) |
468 | =item $json = $json->allow_blessed ([$enable]) |
457 | |
469 | |
458 | =item $enabled = $json->get_allow_blessed |
470 | =item $enabled = $json->get_allow_blessed |
459 | |
471 | |
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472 | See L<OBJECT SERIALISATION> for details. |
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473 | |
460 | If C<$enable> is true (or missing), then the C<encode> method will not |
474 | If C<$enable> is true (or missing), then the C<encode> method will not |
461 | barf when it encounters a blessed reference. Instead, the value of the |
475 | barf when it encounters a blessed reference that it cannot convert |
462 | B<convert_blessed> option will decide whether C<null> (C<convert_blessed> |
476 | otherwise. Instead, a JSON C<null> value is encoded instead of the object. |
463 | disabled or no C<TO_JSON> method found) or a representation of the |
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464 | object (C<convert_blessed> enabled and C<TO_JSON> method found) is being |
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465 | encoded. Has no effect on C<decode>. |
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466 | |
477 | |
467 | If C<$enable> is false (the default), then C<encode> will throw an |
478 | If C<$enable> is false (the default), then C<encode> will throw an |
468 | exception when it encounters a blessed object. |
479 | exception when it encounters a blessed object that it cannot convert |
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480 | otherwise. |
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481 | |
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482 | This setting has no effect on C<decode>. |
469 | |
483 | |
470 | =item $json = $json->convert_blessed ([$enable]) |
484 | =item $json = $json->convert_blessed ([$enable]) |
471 | |
485 | |
472 | =item $enabled = $json->get_convert_blessed |
486 | =item $enabled = $json->get_convert_blessed |
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487 | |
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488 | See L<OBJECT SERIALISATION> for details. |
473 | |
489 | |
474 | If C<$enable> is true (or missing), then C<encode>, upon encountering a |
490 | If C<$enable> is true (or missing), then C<encode>, upon encountering a |
475 | blessed object, will check for the availability of the C<TO_JSON> method |
491 | blessed object, will check for the availability of the C<TO_JSON> method |
476 | on the object's class. If found, it will be called in scalar context |
492 | on the object's class. If found, it will be called in scalar context and |
477 | and the resulting scalar will be encoded instead of the object. If no |
493 | the resulting scalar will be encoded instead of the object. |
478 | C<TO_JSON> method is found, the value of C<allow_blessed> will decide what |
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479 | to do. |
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480 | |
494 | |
481 | The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON> |
495 | The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON> |
482 | returns other blessed objects, those will be handled in the same |
496 | returns other blessed objects, those will be handled in the same |
483 | way. C<TO_JSON> must take care of not causing an endless recursion cycle |
497 | way. C<TO_JSON> must take care of not causing an endless recursion cycle |
484 | (== crash) in this case. The name of C<TO_JSON> was chosen because other |
498 | (== crash) in this case. The name of C<TO_JSON> was chosen because other |
485 | methods called by the Perl core (== not by the user of the object) are |
499 | methods called by the Perl core (== not by the user of the object) are |
486 | usually in upper case letters and to avoid collisions with any C<to_json> |
500 | usually in upper case letters and to avoid collisions with any C<to_json> |
487 | function or method. |
501 | function or method. |
488 | |
502 | |
489 | This setting does not yet influence C<decode> in any way, but in the |
503 | If C<$enable> is false (the default), then C<encode> will not consider |
490 | future, global hooks might get installed that influence C<decode> and are |
504 | this type of conversion. |
491 | enabled by this setting. |
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492 | |
505 | |
493 | If C<$enable> is false, then the C<allow_blessed> setting will decide what |
506 | This setting has no effect on C<decode>. |
494 | to do when a blessed object is found. |
507 | |
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508 | =item $json = $json->allow_tags ([$enable]) |
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509 | |
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510 | =item $enabled = $json->allow_tags |
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511 | |
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512 | See L<OBJECT SERIALISATION> for details. |
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513 | |
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514 | If C<$enable> is true (or missing), then C<encode>, upon encountering a |
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515 | blessed object, will check for the availability of the C<FREEZE> method on |
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516 | the object's class. If found, it will be used to serialise the object into |
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517 | a nonstandard tagged JSON value (that JSON decoders cannot decode). |
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518 | |
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519 | It also causes C<decode> to parse such tagged JSON values and deserialise |
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520 | them via a call to the C<THAW> method. |
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521 | |
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522 | If C<$enable> is false (the default), then C<encode> will not consider |
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523 | this type of conversion, and tagged JSON values will cause a parse error |
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524 | in C<decode>, as if tags were not part of the grammar. |
495 | |
525 | |
496 | =item $json = $json->filter_json_object ([$coderef->($hashref)]) |
526 | =item $json = $json->filter_json_object ([$coderef->($hashref)]) |
497 | |
527 | |
498 | When C<$coderef> is specified, it will be called from C<decode> each |
528 | When C<$coderef> is specified, it will be called from C<decode> each |
499 | time it decodes a JSON object. The only argument is a reference to the |
529 | time it decodes a JSON object. The only argument is a reference to the |
… | |
… | |
600 | =item $json = $json->max_depth ([$maximum_nesting_depth]) |
630 | =item $json = $json->max_depth ([$maximum_nesting_depth]) |
601 | |
631 | |
602 | =item $max_depth = $json->get_max_depth |
632 | =item $max_depth = $json->get_max_depth |
603 | |
633 | |
604 | Sets the maximum nesting level (default C<512>) accepted while encoding |
634 | Sets the maximum nesting level (default C<512>) accepted while encoding |
605 | or decoding. If the JSON text or Perl data structure has an equal or |
635 | or decoding. If a higher nesting level is detected in JSON text or a Perl |
606 | higher nesting level then this limit, then the encoder and decoder will |
636 | data structure, then the encoder and decoder will stop and croak at that |
607 | stop and croak at that point. |
637 | point. |
608 | |
638 | |
609 | Nesting level is defined by number of hash- or arrayrefs that the encoder |
639 | Nesting level is defined by number of hash- or arrayrefs that the encoder |
610 | needs to traverse to reach a given point or the number of C<{> or C<[> |
640 | needs to traverse to reach a given point or the number of C<{> or C<[> |
611 | characters without their matching closing parenthesis crossed to reach a |
641 | characters without their matching closing parenthesis crossed to reach a |
612 | given character in a string. |
642 | given character in a string. |
613 | |
643 | |
614 | Setting the maximum depth to one disallows any nesting, so that ensures |
644 | Setting the maximum depth to one disallows any nesting, so that ensures |
615 | that the object is only a single hash/object or array. |
645 | that the object is only a single hash/object or array. |
616 | |
646 | |
617 | The argument to C<max_depth> will be rounded up to the next highest power |
|
|
618 | of two. If no argument is given, the highest possible setting will be |
647 | If no argument is given, the highest possible setting will be used, which |
619 | used, which is rarely useful. |
648 | is rarely useful. |
|
|
649 | |
|
|
650 | Note that nesting is implemented by recursion in C. The default value has |
|
|
651 | been chosen to be as large as typical operating systems allow without |
|
|
652 | crashing. |
620 | |
653 | |
621 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
654 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
622 | |
655 | |
623 | =item $json = $json->max_size ([$maximum_string_size]) |
656 | =item $json = $json->max_size ([$maximum_string_size]) |
624 | |
657 | |
625 | =item $max_size = $json->get_max_size |
658 | =item $max_size = $json->get_max_size |
626 | |
659 | |
627 | Set the maximum length a JSON text may have (in bytes) where decoding is |
660 | Set the maximum length a JSON text may have (in bytes) where decoding is |
628 | being attempted. The default is C<0>, meaning no limit. When C<decode> |
661 | being attempted. The default is C<0>, meaning no limit. When C<decode> |
629 | is called on a string longer then this number of characters it will not |
662 | is called on a string that is longer then this many bytes, it will not |
630 | attempt to decode the string but throw an exception. This setting has no |
663 | attempt to decode the string but throw an exception. This setting has no |
631 | effect on C<encode> (yet). |
664 | effect on C<encode> (yet). |
632 | |
665 | |
633 | The argument to C<max_size> will be rounded up to the next B<highest> |
666 | If no argument is given, the limit check will be deactivated (same as when |
634 | power of two (so may be more than requested). If no argument is given, the |
667 | C<0> is specified). |
635 | limit check will be deactivated (same as when C<0> is specified). |
|
|
636 | |
668 | |
637 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
669 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
638 | |
670 | |
639 | =item $json_text = $json->encode ($perl_scalar) |
671 | =item $json_text = $json->encode ($perl_scalar) |
640 | |
672 | |
641 | Converts the given Perl data structure (a simple scalar or a reference |
673 | Converts the given Perl value or data structure to its JSON |
642 | to a hash or array) to its JSON representation. Simple scalars will be |
674 | representation. Croaks on error. |
643 | converted into JSON string or number sequences, while references to arrays |
|
|
644 | become JSON arrays and references to hashes become JSON objects. Undefined |
|
|
645 | Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true> |
|
|
646 | nor C<false> values will be generated. |
|
|
647 | |
675 | |
648 | =item $perl_scalar = $json->decode ($json_text) |
676 | =item $perl_scalar = $json->decode ($json_text) |
649 | |
677 | |
650 | The opposite of C<encode>: expects a JSON text and tries to parse it, |
678 | The opposite of C<encode>: expects a JSON text and tries to parse it, |
651 | returning the resulting simple scalar or reference. Croaks on error. |
679 | returning the resulting simple scalar or reference. Croaks on error. |
652 | |
|
|
653 | JSON numbers and strings become simple Perl scalars. JSON arrays become |
|
|
654 | Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes |
|
|
655 | C<1>, C<false> becomes C<0> and C<null> becomes C<undef>. |
|
|
656 | |
680 | |
657 | =item ($perl_scalar, $characters) = $json->decode_prefix ($json_text) |
681 | =item ($perl_scalar, $characters) = $json->decode_prefix ($json_text) |
658 | |
682 | |
659 | This works like the C<decode> method, but instead of raising an exception |
683 | This works like the C<decode> method, but instead of raising an exception |
660 | when there is trailing garbage after the first JSON object, it will |
684 | when there is trailing garbage after the first JSON object, it will |
661 | silently stop parsing there and return the number of characters consumed |
685 | silently stop parsing there and return the number of characters consumed |
662 | so far. |
686 | so far. |
663 | |
687 | |
664 | This is useful if your JSON texts are not delimited by an outer protocol |
688 | This is useful if your JSON texts are not delimited by an outer protocol |
665 | (which is not the brightest thing to do in the first place) and you need |
|
|
666 | to know where the JSON text ends. |
689 | and you need to know where the JSON text ends. |
667 | |
690 | |
668 | JSON::XS->new->decode_prefix ("[1] the tail") |
691 | JSON::XS->new->decode_prefix ("[1] the tail") |
669 | => ([], 3) |
692 | => ([], 3) |
670 | |
693 | |
671 | =back |
694 | =back |
|
|
695 | |
|
|
696 | |
|
|
697 | =head1 INCREMENTAL PARSING |
|
|
698 | |
|
|
699 | In some cases, there is the need for incremental parsing of JSON |
|
|
700 | texts. While this module always has to keep both JSON text and resulting |
|
|
701 | Perl data structure in memory at one time, it does allow you to parse a |
|
|
702 | JSON stream incrementally. It does so by accumulating text until it has |
|
|
703 | a full JSON object, which it then can decode. This process is similar to |
|
|
704 | using C<decode_prefix> to see if a full JSON object is available, but |
|
|
705 | is much more efficient (and can be implemented with a minimum of method |
|
|
706 | calls). |
|
|
707 | |
|
|
708 | JSON::XS will only attempt to parse the JSON text once it is sure it |
|
|
709 | has enough text to get a decisive result, using a very simple but |
|
|
710 | truly incremental parser. This means that it sometimes won't stop as |
|
|
711 | early as the full parser, for example, it doesn't detect mismatched |
|
|
712 | parentheses. The only thing it guarantees is that it starts decoding as |
|
|
713 | soon as a syntactically valid JSON text has been seen. This means you need |
|
|
714 | to set resource limits (e.g. C<max_size>) to ensure the parser will stop |
|
|
715 | parsing in the presence if syntax errors. |
|
|
716 | |
|
|
717 | The following methods implement this incremental parser. |
|
|
718 | |
|
|
719 | =over 4 |
|
|
720 | |
|
|
721 | =item [void, scalar or list context] = $json->incr_parse ([$string]) |
|
|
722 | |
|
|
723 | This is the central parsing function. It can both append new text and |
|
|
724 | extract objects from the stream accumulated so far (both of these |
|
|
725 | functions are optional). |
|
|
726 | |
|
|
727 | If C<$string> is given, then this string is appended to the already |
|
|
728 | existing JSON fragment stored in the C<$json> object. |
|
|
729 | |
|
|
730 | After that, if the function is called in void context, it will simply |
|
|
731 | return without doing anything further. This can be used to add more text |
|
|
732 | in as many chunks as you want. |
|
|
733 | |
|
|
734 | If the method is called in scalar context, then it will try to extract |
|
|
735 | exactly I<one> JSON object. If that is successful, it will return this |
|
|
736 | object, otherwise it will return C<undef>. If there is a parse error, |
|
|
737 | this method will croak just as C<decode> would do (one can then use |
|
|
738 | C<incr_skip> to skip the erroneous part). This is the most common way of |
|
|
739 | using the method. |
|
|
740 | |
|
|
741 | And finally, in list context, it will try to extract as many objects |
|
|
742 | from the stream as it can find and return them, or the empty list |
|
|
743 | otherwise. For this to work, there must be no separators between the JSON |
|
|
744 | objects or arrays, instead they must be concatenated back-to-back. If |
|
|
745 | an error occurs, an exception will be raised as in the scalar context |
|
|
746 | case. Note that in this case, any previously-parsed JSON texts will be |
|
|
747 | lost. |
|
|
748 | |
|
|
749 | Example: Parse some JSON arrays/objects in a given string and return |
|
|
750 | them. |
|
|
751 | |
|
|
752 | my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]"); |
|
|
753 | |
|
|
754 | =item $lvalue_string = $json->incr_text |
|
|
755 | |
|
|
756 | This method returns the currently stored JSON fragment as an lvalue, that |
|
|
757 | is, you can manipulate it. This I<only> works when a preceding call to |
|
|
758 | C<incr_parse> in I<scalar context> successfully returned an object. Under |
|
|
759 | all other circumstances you must not call this function (I mean it. |
|
|
760 | although in simple tests it might actually work, it I<will> fail under |
|
|
761 | real world conditions). As a special exception, you can also call this |
|
|
762 | method before having parsed anything. |
|
|
763 | |
|
|
764 | This function is useful in two cases: a) finding the trailing text after a |
|
|
765 | JSON object or b) parsing multiple JSON objects separated by non-JSON text |
|
|
766 | (such as commas). |
|
|
767 | |
|
|
768 | =item $json->incr_skip |
|
|
769 | |
|
|
770 | This will reset the state of the incremental parser and will remove |
|
|
771 | the parsed text from the input buffer so far. This is useful after |
|
|
772 | C<incr_parse> died, in which case the input buffer and incremental parser |
|
|
773 | state is left unchanged, to skip the text parsed so far and to reset the |
|
|
774 | parse state. |
|
|
775 | |
|
|
776 | The difference to C<incr_reset> is that only text until the parse error |
|
|
777 | occurred is removed. |
|
|
778 | |
|
|
779 | =item $json->incr_reset |
|
|
780 | |
|
|
781 | This completely resets the incremental parser, that is, after this call, |
|
|
782 | it will be as if the parser had never parsed anything. |
|
|
783 | |
|
|
784 | This is useful if you want to repeatedly parse JSON objects and want to |
|
|
785 | ignore any trailing data, which means you have to reset the parser after |
|
|
786 | each successful decode. |
|
|
787 | |
|
|
788 | =back |
|
|
789 | |
|
|
790 | =head2 LIMITATIONS |
|
|
791 | |
|
|
792 | All options that affect decoding are supported, except |
|
|
793 | C<allow_nonref>. The reason for this is that it cannot be made to work |
|
|
794 | sensibly: JSON objects and arrays are self-delimited, i.e. you can |
|
|
795 | concatenate them back to back and still decode them perfectly. This does |
|
|
796 | not hold true for JSON numbers, however. |
|
|
797 | |
|
|
798 | For example, is the string C<1> a single JSON number, or is it simply the |
|
|
799 | start of C<12>? Or is C<12> a single JSON number, or the concatenation |
|
|
800 | of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS |
|
|
801 | takes the conservative route and disallows this case. |
|
|
802 | |
|
|
803 | =head2 EXAMPLES |
|
|
804 | |
|
|
805 | Some examples will make all this clearer. First, a simple example that |
|
|
806 | works similarly to C<decode_prefix>: We want to decode the JSON object at |
|
|
807 | the start of a string and identify the portion after the JSON object: |
|
|
808 | |
|
|
809 | my $text = "[1,2,3] hello"; |
|
|
810 | |
|
|
811 | my $json = new JSON::XS; |
|
|
812 | |
|
|
813 | my $obj = $json->incr_parse ($text) |
|
|
814 | or die "expected JSON object or array at beginning of string"; |
|
|
815 | |
|
|
816 | my $tail = $json->incr_text; |
|
|
817 | # $tail now contains " hello" |
|
|
818 | |
|
|
819 | Easy, isn't it? |
|
|
820 | |
|
|
821 | Now for a more complicated example: Imagine a hypothetical protocol where |
|
|
822 | you read some requests from a TCP stream, and each request is a JSON |
|
|
823 | array, without any separation between them (in fact, it is often useful to |
|
|
824 | use newlines as "separators", as these get interpreted as whitespace at |
|
|
825 | the start of the JSON text, which makes it possible to test said protocol |
|
|
826 | with C<telnet>...). |
|
|
827 | |
|
|
828 | Here is how you'd do it (it is trivial to write this in an event-based |
|
|
829 | manner): |
|
|
830 | |
|
|
831 | my $json = new JSON::XS; |
|
|
832 | |
|
|
833 | # read some data from the socket |
|
|
834 | while (sysread $socket, my $buf, 4096) { |
|
|
835 | |
|
|
836 | # split and decode as many requests as possible |
|
|
837 | for my $request ($json->incr_parse ($buf)) { |
|
|
838 | # act on the $request |
|
|
839 | } |
|
|
840 | } |
|
|
841 | |
|
|
842 | Another complicated example: Assume you have a string with JSON objects |
|
|
843 | or arrays, all separated by (optional) comma characters (e.g. C<[1],[2], |
|
|
844 | [3]>). To parse them, we have to skip the commas between the JSON texts, |
|
|
845 | and here is where the lvalue-ness of C<incr_text> comes in useful: |
|
|
846 | |
|
|
847 | my $text = "[1],[2], [3]"; |
|
|
848 | my $json = new JSON::XS; |
|
|
849 | |
|
|
850 | # void context, so no parsing done |
|
|
851 | $json->incr_parse ($text); |
|
|
852 | |
|
|
853 | # now extract as many objects as possible. note the |
|
|
854 | # use of scalar context so incr_text can be called. |
|
|
855 | while (my $obj = $json->incr_parse) { |
|
|
856 | # do something with $obj |
|
|
857 | |
|
|
858 | # now skip the optional comma |
|
|
859 | $json->incr_text =~ s/^ \s* , //x; |
|
|
860 | } |
|
|
861 | |
|
|
862 | Now lets go for a very complex example: Assume that you have a gigantic |
|
|
863 | JSON array-of-objects, many gigabytes in size, and you want to parse it, |
|
|
864 | but you cannot load it into memory fully (this has actually happened in |
|
|
865 | the real world :). |
|
|
866 | |
|
|
867 | Well, you lost, you have to implement your own JSON parser. But JSON::XS |
|
|
868 | can still help you: You implement a (very simple) array parser and let |
|
|
869 | JSON decode the array elements, which are all full JSON objects on their |
|
|
870 | own (this wouldn't work if the array elements could be JSON numbers, for |
|
|
871 | example): |
|
|
872 | |
|
|
873 | my $json = new JSON::XS; |
|
|
874 | |
|
|
875 | # open the monster |
|
|
876 | open my $fh, "<bigfile.json" |
|
|
877 | or die "bigfile: $!"; |
|
|
878 | |
|
|
879 | # first parse the initial "[" |
|
|
880 | for (;;) { |
|
|
881 | sysread $fh, my $buf, 65536 |
|
|
882 | or die "read error: $!"; |
|
|
883 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
884 | |
|
|
885 | # Exit the loop once we found and removed(!) the initial "[". |
|
|
886 | # In essence, we are (ab-)using the $json object as a simple scalar |
|
|
887 | # we append data to. |
|
|
888 | last if $json->incr_text =~ s/^ \s* \[ //x; |
|
|
889 | } |
|
|
890 | |
|
|
891 | # now we have the skipped the initial "[", so continue |
|
|
892 | # parsing all the elements. |
|
|
893 | for (;;) { |
|
|
894 | # in this loop we read data until we got a single JSON object |
|
|
895 | for (;;) { |
|
|
896 | if (my $obj = $json->incr_parse) { |
|
|
897 | # do something with $obj |
|
|
898 | last; |
|
|
899 | } |
|
|
900 | |
|
|
901 | # add more data |
|
|
902 | sysread $fh, my $buf, 65536 |
|
|
903 | or die "read error: $!"; |
|
|
904 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
905 | } |
|
|
906 | |
|
|
907 | # in this loop we read data until we either found and parsed the |
|
|
908 | # separating "," between elements, or the final "]" |
|
|
909 | for (;;) { |
|
|
910 | # first skip whitespace |
|
|
911 | $json->incr_text =~ s/^\s*//; |
|
|
912 | |
|
|
913 | # if we find "]", we are done |
|
|
914 | if ($json->incr_text =~ s/^\]//) { |
|
|
915 | print "finished.\n"; |
|
|
916 | exit; |
|
|
917 | } |
|
|
918 | |
|
|
919 | # if we find ",", we can continue with the next element |
|
|
920 | if ($json->incr_text =~ s/^,//) { |
|
|
921 | last; |
|
|
922 | } |
|
|
923 | |
|
|
924 | # if we find anything else, we have a parse error! |
|
|
925 | if (length $json->incr_text) { |
|
|
926 | die "parse error near ", $json->incr_text; |
|
|
927 | } |
|
|
928 | |
|
|
929 | # else add more data |
|
|
930 | sysread $fh, my $buf, 65536 |
|
|
931 | or die "read error: $!"; |
|
|
932 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
933 | } |
|
|
934 | |
|
|
935 | This is a complex example, but most of the complexity comes from the fact |
|
|
936 | that we are trying to be correct (bear with me if I am wrong, I never ran |
|
|
937 | the above example :). |
|
|
938 | |
672 | |
939 | |
673 | |
940 | |
674 | =head1 MAPPING |
941 | =head1 MAPPING |
675 | |
942 | |
676 | This section describes how JSON::XS maps Perl values to JSON values and |
943 | This section describes how JSON::XS maps Perl values to JSON values and |
… | |
… | |
706 | |
973 | |
707 | A JSON number becomes either an integer, numeric (floating point) or |
974 | A JSON number becomes either an integer, numeric (floating point) or |
708 | string scalar in perl, depending on its range and any fractional parts. On |
975 | string scalar in perl, depending on its range and any fractional parts. On |
709 | the Perl level, there is no difference between those as Perl handles all |
976 | the Perl level, there is no difference between those as Perl handles all |
710 | the conversion details, but an integer may take slightly less memory and |
977 | the conversion details, but an integer may take slightly less memory and |
711 | might represent more values exactly than (floating point) numbers. |
978 | might represent more values exactly than floating point numbers. |
712 | |
979 | |
713 | If the number consists of digits only, JSON::XS will try to represent |
980 | If the number consists of digits only, JSON::XS will try to represent |
714 | it as an integer value. If that fails, it will try to represent it as |
981 | it as an integer value. If that fails, it will try to represent it as |
715 | a numeric (floating point) value if that is possible without loss of |
982 | a numeric (floating point) value if that is possible without loss of |
716 | precision. Otherwise it will preserve the number as a string value. |
983 | precision. Otherwise it will preserve the number as a string value (in |
|
|
984 | which case you lose roundtripping ability, as the JSON number will be |
|
|
985 | re-encoded to a JSON string). |
717 | |
986 | |
718 | Numbers containing a fractional or exponential part will always be |
987 | Numbers containing a fractional or exponential part will always be |
719 | represented as numeric (floating point) values, possibly at a loss of |
988 | represented as numeric (floating point) values, possibly at a loss of |
720 | precision. |
989 | precision (in which case you might lose perfect roundtripping ability, but |
|
|
990 | the JSON number will still be re-encoded as a JSON number). |
721 | |
991 | |
722 | This might create round-tripping problems as numbers might become strings, |
992 | Note that precision is not accuracy - binary floating point values cannot |
723 | but as Perl is typeless there is no other way to do it. |
993 | represent most decimal fractions exactly, and when converting from and to |
|
|
994 | floating point, JSON::XS only guarantees precision up to but not including |
|
|
995 | the least significant bit. |
724 | |
996 | |
725 | =item true, false |
997 | =item true, false |
726 | |
998 | |
727 | These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, |
999 | These JSON atoms become C<Types::Serialiser::true> and |
728 | respectively. They are overloaded to act almost exactly like the numbers |
1000 | C<Types::Serialiser::false>, respectively. They are overloaded to act |
729 | C<1> and C<0>. You can check whether a scalar is a JSON boolean by using |
1001 | almost exactly like the numbers C<1> and C<0>. You can check whether |
730 | the C<JSON::XS::is_bool> function. |
1002 | a scalar is a JSON boolean by using the C<Types::Serialiser::is_bool> |
|
|
1003 | function (after C<use Types::Serialier>, of course). |
731 | |
1004 | |
732 | =item null |
1005 | =item null |
733 | |
1006 | |
734 | A JSON null atom becomes C<undef> in Perl. |
1007 | A JSON null atom becomes C<undef> in Perl. |
|
|
1008 | |
|
|
1009 | =item shell-style comments (C<< # I<text> >>) |
|
|
1010 | |
|
|
1011 | As a nonstandard extension to the JSON syntax that is enabled by the |
|
|
1012 | C<relaxed> setting, shell-style comments are allowed. They can start |
|
|
1013 | anywhere outside strings and go till the end of the line. |
|
|
1014 | |
|
|
1015 | =item tagged values (C<< (I<tag>)I<value> >>). |
|
|
1016 | |
|
|
1017 | Another nonstandard extension to the JSON syntax, enabled with the |
|
|
1018 | C<allow_tags> setting, are tagged values. In this implementation, the |
|
|
1019 | I<tag> must be a perl package/class name encoded as a JSON string, and the |
|
|
1020 | I<value> must be a JSON array encoding optional constructor arguments. |
|
|
1021 | |
|
|
1022 | See L<OBJECT SERIALISATION>, below, for details. |
735 | |
1023 | |
736 | =back |
1024 | =back |
737 | |
1025 | |
738 | |
1026 | |
739 | =head2 PERL -> JSON |
1027 | =head2 PERL -> JSON |
… | |
… | |
744 | |
1032 | |
745 | =over 4 |
1033 | =over 4 |
746 | |
1034 | |
747 | =item hash references |
1035 | =item hash references |
748 | |
1036 | |
749 | Perl hash references become JSON objects. As there is no inherent ordering |
1037 | Perl hash references become JSON objects. As there is no inherent |
750 | in hash keys (or JSON objects), they will usually be encoded in a |
1038 | ordering in hash keys (or JSON objects), they will usually be encoded |
751 | pseudo-random order that can change between runs of the same program but |
1039 | in a pseudo-random order. JSON::XS can optionally sort the hash keys |
752 | stays generally the same within a single run of a program. JSON::XS can |
1040 | (determined by the I<canonical> flag), so the same datastructure will |
753 | optionally sort the hash keys (determined by the I<canonical> flag), so |
1041 | serialise to the same JSON text (given same settings and version of |
754 | the same datastructure will serialise to the same JSON text (given same |
1042 | JSON::XS), but this incurs a runtime overhead and is only rarely useful, |
755 | settings and version of JSON::XS), but this incurs a runtime overhead |
1043 | e.g. when you want to compare some JSON text against another for equality. |
756 | and is only rarely useful, e.g. when you want to compare some JSON text |
|
|
757 | against another for equality. |
|
|
758 | |
1044 | |
759 | =item array references |
1045 | =item array references |
760 | |
1046 | |
761 | Perl array references become JSON arrays. |
1047 | Perl array references become JSON arrays. |
762 | |
1048 | |
763 | =item other references |
1049 | =item other references |
764 | |
1050 | |
765 | Other unblessed references are generally not allowed and will cause an |
1051 | Other unblessed references are generally not allowed and will cause an |
766 | exception to be thrown, except for references to the integers C<0> and |
1052 | exception to be thrown, except for references to the integers C<0> and |
767 | C<1>, which get turned into C<false> and C<true> atoms in JSON. You can |
1053 | C<1>, which get turned into C<false> and C<true> atoms in JSON. |
768 | also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. |
|
|
769 | |
1054 | |
|
|
1055 | Since C<JSON::XS> uses the boolean model from L<Types::Serialiser>, you |
|
|
1056 | can also C<use Types::Serialiser> and then use C<Types::Serialiser::false> |
|
|
1057 | and C<Types::Serialiser::true> to improve readability. |
|
|
1058 | |
|
|
1059 | use Types::Serialiser; |
770 | encode_json [\0,JSON::XS::true] # yields [false,true] |
1060 | encode_json [\0, Types::Serialiser::true] # yields [false,true] |
771 | |
1061 | |
772 | =item JSON::XS::true, JSON::XS::false |
1062 | =item Types::Serialiser::true, Types::Serialiser::false |
773 | |
1063 | |
774 | These special values become JSON true and JSON false values, |
1064 | These special values from the L<Types::Serialiser> module become JSON true |
775 | respectively. You can also use C<\1> and C<\0> directly if you want. |
1065 | and JSON false values, respectively. You can also use C<\1> and C<\0> |
|
|
1066 | directly if you want. |
776 | |
1067 | |
777 | =item blessed objects |
1068 | =item blessed objects |
778 | |
1069 | |
779 | Blessed objects are not allowed. JSON::XS currently tries to encode their |
1070 | Blessed objects are not directly representable in JSON, but C<JSON::XS> |
780 | underlying representation (hash- or arrayref), but this behaviour might |
1071 | allows various ways of handling objects. See L<OBJECT SERIALISATION>, |
781 | change in future versions. |
1072 | below, for details. |
782 | |
1073 | |
783 | =item simple scalars |
1074 | =item simple scalars |
784 | |
1075 | |
785 | Simple Perl scalars (any scalar that is not a reference) are the most |
1076 | Simple Perl scalars (any scalar that is not a reference) are the most |
786 | difficult objects to encode: JSON::XS will encode undefined scalars as |
1077 | difficult objects to encode: JSON::XS will encode undefined scalars as |
787 | JSON null value, scalars that have last been used in a string context |
1078 | JSON C<null> values, scalars that have last been used in a string context |
788 | before encoding as JSON strings and anything else as number value: |
1079 | before encoding as JSON strings, and anything else as number value: |
789 | |
1080 | |
790 | # dump as number |
1081 | # dump as number |
791 | encode_json [2] # yields [2] |
1082 | encode_json [2] # yields [2] |
792 | encode_json [-3.0e17] # yields [-3e+17] |
1083 | encode_json [-3.0e17] # yields [-3e+17] |
793 | my $value = 5; encode_json [$value] # yields [5] |
1084 | my $value = 5; encode_json [$value] # yields [5] |
… | |
… | |
811 | my $x = "3"; # some variable containing a string |
1102 | my $x = "3"; # some variable containing a string |
812 | $x += 0; # numify it, ensuring it will be dumped as a number |
1103 | $x += 0; # numify it, ensuring it will be dumped as a number |
813 | $x *= 1; # same thing, the choice is yours. |
1104 | $x *= 1; # same thing, the choice is yours. |
814 | |
1105 | |
815 | You can not currently force the type in other, less obscure, ways. Tell me |
1106 | You can not currently force the type in other, less obscure, ways. Tell me |
816 | if you need this capability. |
1107 | if you need this capability (but don't forget to explain why it's needed |
|
|
1108 | :). |
|
|
1109 | |
|
|
1110 | Note that numerical precision has the same meaning as under Perl (so |
|
|
1111 | binary to decimal conversion follows the same rules as in Perl, which |
|
|
1112 | can differ to other languages). Also, your perl interpreter might expose |
|
|
1113 | extensions to the floating point numbers of your platform, such as |
|
|
1114 | infinities or NaN's - these cannot be represented in JSON, and it is an |
|
|
1115 | error to pass those in. |
817 | |
1116 | |
818 | =back |
1117 | =back |
819 | |
1118 | |
|
|
1119 | =head2 OBJECT SERIALISATION |
820 | |
1120 | |
821 | =head1 COMPARISON |
1121 | As JSON cannot directly represent Perl objects, you have to choose between |
|
|
1122 | a pure JSON representation (without the ability to deserialise the object |
|
|
1123 | automatically again), and a nonstandard extension to the JSON syntax, |
|
|
1124 | tagged values. |
822 | |
1125 | |
823 | As already mentioned, this module was created because none of the existing |
1126 | =head3 SERIALISATION |
824 | JSON modules could be made to work correctly. First I will describe the |
1127 | |
825 | problems (or pleasures) I encountered with various existing JSON modules, |
1128 | What happens when C<JSON::XS> encounters a Perl object depends on the |
826 | followed by some benchmark values. JSON::XS was designed not to suffer |
1129 | C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are |
827 | from any of these problems or limitations. |
1130 | used in this order: |
828 | |
1131 | |
829 | =over 4 |
1132 | =over 4 |
830 | |
1133 | |
831 | =item JSON 1.07 |
1134 | =item 1. C<allow_tags> is enabled and the object has a C<FREEZE> method. |
832 | |
1135 | |
833 | Slow (but very portable, as it is written in pure Perl). |
1136 | In this case, C<JSON::XS> uses the L<Types::Serialiser> object |
|
|
1137 | serialisation protocol to create a tagged JSON value, using a nonstandard |
|
|
1138 | extension to the JSON syntax. |
834 | |
1139 | |
835 | Undocumented/buggy Unicode handling (how JSON handles Unicode values is |
1140 | This works by invoking the C<FREEZE> method on the object, with the first |
836 | undocumented. One can get far by feeding it Unicode strings and doing |
1141 | argument being the object to serialise, and the second argument being the |
837 | en-/decoding oneself, but Unicode escapes are not working properly). |
1142 | constant string C<JSON> to distinguish it from other serialisers. |
838 | |
1143 | |
839 | No round-tripping (strings get clobbered if they look like numbers, e.g. |
1144 | The C<FREEZE> method can return any number of values (i.e. zero or |
840 | the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will |
1145 | more). These values and the paclkage/classname of the object will then be |
841 | decode into the number 2. |
1146 | encoded as a tagged JSON value in the following format: |
842 | |
1147 | |
843 | =item JSON::PC 0.01 |
1148 | ("classname")[FREEZE return values...] |
844 | |
1149 | |
845 | Very fast. |
1150 | e.g.: |
846 | |
1151 | |
847 | Undocumented/buggy Unicode handling. |
1152 | ("URI")["http://www.google.com/"] |
|
|
1153 | ("MyDate")[2013,10,29] |
|
|
1154 | ("ImageData::JPEG")["Z3...VlCg=="] |
848 | |
1155 | |
849 | No round-tripping. |
1156 | For example, the hypothetical C<My::Object> C<FREEZE> method might use the |
|
|
1157 | objects C<type> and C<id> members to encode the object: |
850 | |
1158 | |
851 | Has problems handling many Perl values (e.g. regex results and other magic |
1159 | sub My::Object::FREEZE { |
852 | values will make it croak). |
1160 | my ($self, $serialiser) = @_; |
853 | |
1161 | |
854 | Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> |
1162 | ($self->{type}, $self->{id}) |
855 | which is not a valid JSON text. |
1163 | } |
856 | |
1164 | |
857 | Unmaintained (maintainer unresponsive for many months, bugs are not |
1165 | =item 2. C<convert_blessed> is enabled and the object has a C<TO_JSON> method. |
858 | getting fixed). |
|
|
859 | |
1166 | |
860 | =item JSON::Syck 0.21 |
1167 | In this case, the C<TO_JSON> method of the object is invoked in scalar |
|
|
1168 | context. It must return a single scalar that can be directly encoded into |
|
|
1169 | JSON. This scalar replaces the object in the JSON text. |
861 | |
1170 | |
862 | Very buggy (often crashes). |
1171 | For example, the following C<TO_JSON> method will convert all L<URI> |
|
|
1172 | objects to JSON strings when serialised. The fatc that these values |
|
|
1173 | originally were L<URI> objects is lost. |
863 | |
1174 | |
864 | Very inflexible (no human-readable format supported, format pretty much |
1175 | sub URI::TO_JSON { |
865 | undocumented. I need at least a format for easy reading by humans and a |
1176 | my ($uri) = @_; |
866 | single-line compact format for use in a protocol, and preferably a way to |
1177 | $uri->as_string |
867 | generate ASCII-only JSON texts). |
1178 | } |
868 | |
1179 | |
869 | Completely broken (and confusingly documented) Unicode handling (Unicode |
1180 | =item 3. C<allow_blessed> is enabled. |
870 | escapes are not working properly, you need to set ImplicitUnicode to |
|
|
871 | I<different> values on en- and decoding to get symmetric behaviour). |
|
|
872 | |
1181 | |
873 | No round-tripping (simple cases work, but this depends on whether the scalar |
1182 | The object will be serialised as a JSON null value. |
874 | value was used in a numeric context or not). |
|
|
875 | |
1183 | |
876 | Dumping hashes may skip hash values depending on iterator state. |
1184 | =item 4. none of the above |
877 | |
1185 | |
878 | Unmaintained (maintainer unresponsive for many months, bugs are not |
1186 | If none of the settings are enabled or the respective methods are missing, |
879 | getting fixed). |
1187 | C<JSON::XS> throws an exception. |
880 | |
|
|
881 | Does not check input for validity (i.e. will accept non-JSON input and |
|
|
882 | return "something" instead of raising an exception. This is a security |
|
|
883 | issue: imagine two banks transferring money between each other using |
|
|
884 | JSON. One bank might parse a given non-JSON request and deduct money, |
|
|
885 | while the other might reject the transaction with a syntax error. While a |
|
|
886 | good protocol will at least recover, that is extra unnecessary work and |
|
|
887 | the transaction will still not succeed). |
|
|
888 | |
|
|
889 | =item JSON::DWIW 0.04 |
|
|
890 | |
|
|
891 | Very fast. Very natural. Very nice. |
|
|
892 | |
|
|
893 | Undocumented Unicode handling (but the best of the pack. Unicode escapes |
|
|
894 | still don't get parsed properly). |
|
|
895 | |
|
|
896 | Very inflexible. |
|
|
897 | |
|
|
898 | No round-tripping. |
|
|
899 | |
|
|
900 | Does not generate valid JSON texts (key strings are often unquoted, empty keys |
|
|
901 | result in nothing being output) |
|
|
902 | |
|
|
903 | Does not check input for validity. |
|
|
904 | |
1188 | |
905 | =back |
1189 | =back |
906 | |
1190 | |
|
|
1191 | =head3 DESERIALISATION |
|
|
1192 | |
|
|
1193 | For deserialisation there are only two cases to consider: either |
|
|
1194 | nonstandard tagging was used, in which case C<allow_tags> decides, |
|
|
1195 | or objects cannot be automatically be deserialised, in which |
|
|
1196 | case you can use postprocessing or the C<filter_json_object> or |
|
|
1197 | C<filter_json_single_key_object> callbacks to get some real objects our of |
|
|
1198 | your JSON. |
|
|
1199 | |
|
|
1200 | This section only considers the tagged value case: I a tagged JSON object |
|
|
1201 | is encountered during decoding and C<allow_tags> is disabled, a parse |
|
|
1202 | error will result (as if tagged values were not part of the grammar). |
|
|
1203 | |
|
|
1204 | If C<allow_tags> is enabled, C<JSON::XS> will look up the C<THAW> method |
|
|
1205 | of the package/classname used during serialisation (it will not attempt |
|
|
1206 | to load the package as a Perl module). If there is no such method, the |
|
|
1207 | decoding will fail with an error. |
|
|
1208 | |
|
|
1209 | Otherwise, the C<THAW> method is invoked with the classname as first |
|
|
1210 | argument, the constant string C<JSON> as second argument, and all the |
|
|
1211 | values from the JSON array (the values originally returned by the |
|
|
1212 | C<FREEZE> method) as remaining arguments. |
|
|
1213 | |
|
|
1214 | The method must then return the object. While technically you can return |
|
|
1215 | any Perl scalar, you might have to enable the C<enable_nonref> setting to |
|
|
1216 | make that work in all cases, so better return an actual blessed reference. |
|
|
1217 | |
|
|
1218 | As an example, let's implement a C<THAW> function that regenerates the |
|
|
1219 | C<My::Object> from the C<FREEZE> example earlier: |
|
|
1220 | |
|
|
1221 | sub My::Object::THAW { |
|
|
1222 | my ($class, $serialiser, $type, $id) = @_; |
|
|
1223 | |
|
|
1224 | $class->new (type => $type, id => $id) |
|
|
1225 | } |
|
|
1226 | |
|
|
1227 | |
|
|
1228 | =head1 ENCODING/CODESET FLAG NOTES |
|
|
1229 | |
|
|
1230 | The interested reader might have seen a number of flags that signify |
|
|
1231 | encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be |
|
|
1232 | some confusion on what these do, so here is a short comparison: |
|
|
1233 | |
|
|
1234 | C<utf8> controls whether the JSON text created by C<encode> (and expected |
|
|
1235 | by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only |
|
|
1236 | control whether C<encode> escapes character values outside their respective |
|
|
1237 | codeset range. Neither of these flags conflict with each other, although |
|
|
1238 | some combinations make less sense than others. |
|
|
1239 | |
|
|
1240 | Care has been taken to make all flags symmetrical with respect to |
|
|
1241 | C<encode> and C<decode>, that is, texts encoded with any combination of |
|
|
1242 | these flag values will be correctly decoded when the same flags are used |
|
|
1243 | - in general, if you use different flag settings while encoding vs. when |
|
|
1244 | decoding you likely have a bug somewhere. |
|
|
1245 | |
|
|
1246 | Below comes a verbose discussion of these flags. Note that a "codeset" is |
|
|
1247 | simply an abstract set of character-codepoint pairs, while an encoding |
|
|
1248 | takes those codepoint numbers and I<encodes> them, in our case into |
|
|
1249 | octets. Unicode is (among other things) a codeset, UTF-8 is an encoding, |
|
|
1250 | and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at |
|
|
1251 | the same time, which can be confusing. |
|
|
1252 | |
|
|
1253 | =over 4 |
|
|
1254 | |
|
|
1255 | =item C<utf8> flag disabled |
|
|
1256 | |
|
|
1257 | When C<utf8> is disabled (the default), then C<encode>/C<decode> generate |
|
|
1258 | and expect Unicode strings, that is, characters with high ordinal Unicode |
|
|
1259 | values (> 255) will be encoded as such characters, and likewise such |
|
|
1260 | characters are decoded as-is, no changes to them will be done, except |
|
|
1261 | "(re-)interpreting" them as Unicode codepoints or Unicode characters, |
|
|
1262 | respectively (to Perl, these are the same thing in strings unless you do |
|
|
1263 | funny/weird/dumb stuff). |
|
|
1264 | |
|
|
1265 | This is useful when you want to do the encoding yourself (e.g. when you |
|
|
1266 | want to have UTF-16 encoded JSON texts) or when some other layer does |
|
|
1267 | the encoding for you (for example, when printing to a terminal using a |
|
|
1268 | filehandle that transparently encodes to UTF-8 you certainly do NOT want |
|
|
1269 | to UTF-8 encode your data first and have Perl encode it another time). |
|
|
1270 | |
|
|
1271 | =item C<utf8> flag enabled |
|
|
1272 | |
|
|
1273 | If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all |
|
|
1274 | characters using the corresponding UTF-8 multi-byte sequence, and will |
|
|
1275 | expect your input strings to be encoded as UTF-8, that is, no "character" |
|
|
1276 | of the input string must have any value > 255, as UTF-8 does not allow |
|
|
1277 | that. |
|
|
1278 | |
|
|
1279 | The C<utf8> flag therefore switches between two modes: disabled means you |
|
|
1280 | will get a Unicode string in Perl, enabled means you get an UTF-8 encoded |
|
|
1281 | octet/binary string in Perl. |
|
|
1282 | |
|
|
1283 | =item C<latin1> or C<ascii> flags enabled |
|
|
1284 | |
|
|
1285 | With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters |
|
|
1286 | with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining |
|
|
1287 | characters as specified by the C<utf8> flag. |
|
|
1288 | |
|
|
1289 | If C<utf8> is disabled, then the result is also correctly encoded in those |
|
|
1290 | character sets (as both are proper subsets of Unicode, meaning that a |
|
|
1291 | Unicode string with all character values < 256 is the same thing as a |
|
|
1292 | ISO-8859-1 string, and a Unicode string with all character values < 128 is |
|
|
1293 | the same thing as an ASCII string in Perl). |
|
|
1294 | |
|
|
1295 | If C<utf8> is enabled, you still get a correct UTF-8-encoded string, |
|
|
1296 | regardless of these flags, just some more characters will be escaped using |
|
|
1297 | C<\uXXXX> then before. |
|
|
1298 | |
|
|
1299 | Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8 |
|
|
1300 | encoding, while ASCII-encoded strings are. That is because the ISO-8859-1 |
|
|
1301 | encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being |
|
|
1302 | a subset of Unicode), while ASCII is. |
|
|
1303 | |
|
|
1304 | Surprisingly, C<decode> will ignore these flags and so treat all input |
|
|
1305 | values as governed by the C<utf8> flag. If it is disabled, this allows you |
|
|
1306 | to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of |
|
|
1307 | Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings. |
|
|
1308 | |
|
|
1309 | So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag - |
|
|
1310 | they only govern when the JSON output engine escapes a character or not. |
|
|
1311 | |
|
|
1312 | The main use for C<latin1> is to relatively efficiently store binary data |
|
|
1313 | as JSON, at the expense of breaking compatibility with most JSON decoders. |
|
|
1314 | |
|
|
1315 | The main use for C<ascii> is to force the output to not contain characters |
|
|
1316 | with values > 127, which means you can interpret the resulting string |
|
|
1317 | as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and |
|
|
1318 | 8-bit-encoding, and still get the same data structure back. This is useful |
|
|
1319 | when your channel for JSON transfer is not 8-bit clean or the encoding |
|
|
1320 | might be mangled in between (e.g. in mail), and works because ASCII is a |
|
|
1321 | proper subset of most 8-bit and multibyte encodings in use in the world. |
|
|
1322 | |
|
|
1323 | =back |
|
|
1324 | |
|
|
1325 | |
|
|
1326 | =head2 JSON and ECMAscript |
|
|
1327 | |
|
|
1328 | JSON syntax is based on how literals are represented in javascript (the |
|
|
1329 | not-standardised predecessor of ECMAscript) which is presumably why it is |
|
|
1330 | called "JavaScript Object Notation". |
|
|
1331 | |
|
|
1332 | However, JSON is not a subset (and also not a superset of course) of |
|
|
1333 | ECMAscript (the standard) or javascript (whatever browsers actually |
|
|
1334 | implement). |
|
|
1335 | |
|
|
1336 | If you want to use javascript's C<eval> function to "parse" JSON, you |
|
|
1337 | might run into parse errors for valid JSON texts, or the resulting data |
|
|
1338 | structure might not be queryable: |
|
|
1339 | |
|
|
1340 | One of the problems is that U+2028 and U+2029 are valid characters inside |
|
|
1341 | JSON strings, but are not allowed in ECMAscript string literals, so the |
|
|
1342 | following Perl fragment will not output something that can be guaranteed |
|
|
1343 | to be parsable by javascript's C<eval>: |
|
|
1344 | |
|
|
1345 | use JSON::XS; |
|
|
1346 | |
|
|
1347 | print encode_json [chr 0x2028]; |
|
|
1348 | |
|
|
1349 | The right fix for this is to use a proper JSON parser in your javascript |
|
|
1350 | programs, and not rely on C<eval> (see for example Douglas Crockford's |
|
|
1351 | F<json2.js> parser). |
|
|
1352 | |
|
|
1353 | If this is not an option, you can, as a stop-gap measure, simply encode to |
|
|
1354 | ASCII-only JSON: |
|
|
1355 | |
|
|
1356 | use JSON::XS; |
|
|
1357 | |
|
|
1358 | print JSON::XS->new->ascii->encode ([chr 0x2028]); |
|
|
1359 | |
|
|
1360 | Note that this will enlarge the resulting JSON text quite a bit if you |
|
|
1361 | have many non-ASCII characters. You might be tempted to run some regexes |
|
|
1362 | to only escape U+2028 and U+2029, e.g.: |
|
|
1363 | |
|
|
1364 | # DO NOT USE THIS! |
|
|
1365 | my $json = JSON::XS->new->utf8->encode ([chr 0x2028]); |
|
|
1366 | $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028 |
|
|
1367 | $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029 |
|
|
1368 | print $json; |
|
|
1369 | |
|
|
1370 | Note that I<this is a bad idea>: the above only works for U+2028 and |
|
|
1371 | U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing |
|
|
1372 | javascript implementations, however, have issues with other characters as |
|
|
1373 | well - using C<eval> naively simply I<will> cause problems. |
|
|
1374 | |
|
|
1375 | Another problem is that some javascript implementations reserve |
|
|
1376 | some property names for their own purposes (which probably makes |
|
|
1377 | them non-ECMAscript-compliant). For example, Iceweasel reserves the |
|
|
1378 | C<__proto__> property name for its own purposes. |
|
|
1379 | |
|
|
1380 | If that is a problem, you could parse try to filter the resulting JSON |
|
|
1381 | output for these property strings, e.g.: |
|
|
1382 | |
|
|
1383 | $json =~ s/"__proto__"\s*:/"__proto__renamed":/g; |
|
|
1384 | |
|
|
1385 | This works because C<__proto__> is not valid outside of strings, so every |
|
|
1386 | occurrence of C<"__proto__"\s*:> must be a string used as property name. |
|
|
1387 | |
|
|
1388 | If you know of other incompatibilities, please let me know. |
|
|
1389 | |
907 | |
1390 | |
908 | =head2 JSON and YAML |
1391 | =head2 JSON and YAML |
909 | |
1392 | |
910 | You often hear that JSON is a subset of YAML. This is, however, a mass |
1393 | You often hear that JSON is a subset of YAML. This is, however, a mass |
911 | hysteria(*) and very far from the truth. In general, there is no way to |
1394 | hysteria(*) and very far from the truth (as of the time of this writing), |
|
|
1395 | so let me state it clearly: I<in general, there is no way to configure |
912 | configure JSON::XS to output a data structure as valid YAML that works for |
1396 | JSON::XS to output a data structure as valid YAML> that works in all |
913 | all cases. |
1397 | cases. |
914 | |
1398 | |
915 | If you really must use JSON::XS to generate YAML, you should use this |
1399 | If you really must use JSON::XS to generate YAML, you should use this |
916 | algorithm (subject to change in future versions): |
1400 | algorithm (subject to change in future versions): |
917 | |
1401 | |
918 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
1402 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
919 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
1403 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
920 | |
1404 | |
921 | This will usually generate JSON texts that also parse as valid |
1405 | This will I<usually> generate JSON texts that also parse as valid |
922 | YAML. Please note that YAML has hardcoded limits on (simple) object key |
1406 | YAML. Please note that YAML has hardcoded limits on (simple) object key |
923 | lengths that JSON doesn't have and also has different and incompatible |
1407 | lengths that JSON doesn't have and also has different and incompatible |
924 | unicode handling, so you should make sure that your hash keys are |
1408 | unicode character escape syntax, so you should make sure that your hash |
925 | noticeably shorter than the 1024 "stream characters" YAML allows and that |
1409 | keys are noticeably shorter than the 1024 "stream characters" YAML allows |
926 | you do not have codepoints with values outside the Unicode BMP (basic |
1410 | and that you do not have characters with codepoint values outside the |
927 | multilingual page). YAML also does not allow C<\/> sequences in strings |
1411 | Unicode BMP (basic multilingual page). YAML also does not allow C<\/> |
928 | (which JSON::XS does not I<currently> generate). |
1412 | sequences in strings (which JSON::XS does not I<currently> generate, but |
|
|
1413 | other JSON generators might). |
929 | |
1414 | |
930 | There might be other incompatibilities that I am not aware of. In general |
1415 | There might be other incompatibilities that I am not aware of (or the YAML |
|
|
1416 | specification has been changed yet again - it does so quite often). In |
931 | you should not try to generate YAML with a JSON generator or vice versa, |
1417 | general you should not try to generate YAML with a JSON generator or vice |
932 | or try to parse JSON with a YAML parser or vice versa: chances are high |
1418 | versa, or try to parse JSON with a YAML parser or vice versa: chances are |
933 | that you will run into severe interoperability problems when you least |
1419 | high that you will run into severe interoperability problems when you |
934 | expect it. |
1420 | least expect it. |
935 | |
1421 | |
936 | =over 4 |
1422 | =over 4 |
937 | |
1423 | |
938 | =item (*) |
1424 | =item (*) |
939 | |
1425 | |
940 | This is spread actively by the YAML team, however. For many years now they |
1426 | I have been pressured multiple times by Brian Ingerson (one of the |
941 | claim YAML were a superset of JSON, even when proven otherwise. |
1427 | authors of the YAML specification) to remove this paragraph, despite him |
|
|
1428 | acknowledging that the actual incompatibilities exist. As I was personally |
|
|
1429 | bitten by this "JSON is YAML" lie, I refused and said I will continue to |
|
|
1430 | educate people about these issues, so others do not run into the same |
|
|
1431 | problem again and again. After this, Brian called me a (quote)I<complete |
|
|
1432 | and worthless idiot>(unquote). |
942 | |
1433 | |
943 | Even the author of this manpage was at some point accused of providing |
1434 | In my opinion, instead of pressuring and insulting people who actually |
944 | "incorrect" information, despite the evidence presented (claims ranged |
1435 | clarify issues with YAML and the wrong statements of some of its |
945 | from "your documentation contains inaccurate and negative statements about |
1436 | proponents, I would kindly suggest reading the JSON spec (which is not |
946 | YAML" (the only negative comment is this footnote, and it didn't exist |
1437 | that difficult or long) and finally make YAML compatible to it, and |
947 | back then; the question on which claims were inaccurate was never answered |
1438 | educating users about the changes, instead of spreading lies about the |
948 | etc.) to "the YAML spec is not up-to-date" (the *real* and suppsedly |
1439 | real compatibility for many I<years> and trying to silence people who |
949 | JSON-compatible spec is apparently not currently publicly available) |
1440 | point out that it isn't true. |
950 | to actual requests to replace this section by *incorrect* information, |
|
|
951 | suppressing information about the real problem). |
|
|
952 | |
1441 | |
953 | So whenever you are told that YAML was a superset of JSON, first check |
1442 | Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even |
954 | wether it is really true (it might be when you check it, but it cetrainly |
1443 | though the incompatibilities have been documented (and are known to Brian) |
955 | is not true when this was written). I would much prefer if the YAML team |
1444 | for many years and the spec makes explicit claims that YAML is a superset |
956 | would spent their time on actually making JSON compatibility a truth |
1445 | of JSON. It would be so easy to fix, but apparently, bullying people and |
957 | (JSON, after all, has a very small and simple specification) instead of |
1446 | corrupting userdata is so much easier. |
958 | trying to lobby/force people into reporting untruths. |
|
|
959 | |
1447 | |
960 | =back |
1448 | =back |
961 | |
1449 | |
962 | |
1450 | |
963 | =head2 SPEED |
1451 | =head2 SPEED |
… | |
… | |
965 | It seems that JSON::XS is surprisingly fast, as shown in the following |
1453 | It seems that JSON::XS is surprisingly fast, as shown in the following |
966 | tables. They have been generated with the help of the C<eg/bench> program |
1454 | tables. They have been generated with the help of the C<eg/bench> program |
967 | in the JSON::XS distribution, to make it easy to compare on your own |
1455 | in the JSON::XS distribution, to make it easy to compare on your own |
968 | system. |
1456 | system. |
969 | |
1457 | |
970 | First comes a comparison between various modules using a very short |
1458 | First comes a comparison between various modules using |
971 | single-line JSON string: |
1459 | a very short single-line JSON string (also available at |
|
|
1460 | L<http://dist.schmorp.de/misc/json/short.json>). |
972 | |
1461 | |
973 | {"method": "handleMessage", "params": ["user1", "we were just talking"], \ |
1462 | {"method": "handleMessage", "params": ["user1", |
974 | "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} |
1463 | "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7, |
|
|
1464 | 1, 0]} |
975 | |
1465 | |
976 | It shows the number of encodes/decodes per second (JSON::XS uses |
1466 | It shows the number of encodes/decodes per second (JSON::XS uses |
977 | the functional interface, while JSON::XS/2 uses the OO interface |
1467 | the functional interface, while JSON::XS/2 uses the OO interface |
978 | with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables |
1468 | with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables |
979 | shrink). Higher is better: |
1469 | shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ |
|
|
1470 | uses the from_json method). Higher is better: |
980 | |
1471 | |
981 | module | encode | decode | |
1472 | module | encode | decode | |
982 | -----------|------------|------------| |
1473 | --------------|------------|------------| |
983 | JSON 1.x | 4990.842 | 4088.813 | |
1474 | JSON::DWIW/DS | 86302.551 | 102300.098 | |
984 | JSON::DWIW | 51653.990 | 71575.154 | |
1475 | JSON::DWIW/FJ | 86302.551 | 75983.768 | |
985 | JSON::PC | 65948.176 | 74631.744 | |
1476 | JSON::PP | 15827.562 | 6638.658 | |
986 | JSON::PP | 8931.652 | 3817.168 | |
1477 | JSON::Syck | 63358.066 | 47662.545 | |
987 | JSON::Syck | 24877.248 | 27776.848 | |
1478 | JSON::XS | 511500.488 | 511500.488 | |
988 | JSON::XS | 388361.481 | 227951.304 | |
1479 | JSON::XS/2 | 291271.111 | 388361.481 | |
989 | JSON::XS/2 | 227951.304 | 218453.333 | |
1480 | JSON::XS/3 | 361577.931 | 361577.931 | |
990 | JSON::XS/3 | 338250.323 | 218453.333 | |
1481 | Storable | 66788.280 | 265462.278 | |
991 | Storable | 16500.016 | 135300.129 | |
|
|
992 | -----------+------------+------------+ |
1482 | --------------+------------+------------+ |
993 | |
1483 | |
994 | That is, JSON::XS is about five times faster than JSON::DWIW on encoding, |
1484 | That is, JSON::XS is almost six times faster than JSON::DWIW on encoding, |
995 | about three times faster on decoding, and over forty times faster |
1485 | about five times faster on decoding, and over thirty to seventy times |
996 | than JSON, even with pretty-printing and key sorting. It also compares |
1486 | faster than JSON's pure perl implementation. It also compares favourably |
997 | favourably to Storable for small amounts of data. |
1487 | to Storable for small amounts of data. |
998 | |
1488 | |
999 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
1489 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
1000 | search API (http://nanoref.com/yahooapis/mgPdGg): |
1490 | search API (L<http://dist.schmorp.de/misc/json/long.json>). |
1001 | |
1491 | |
1002 | module | encode | decode | |
1492 | module | encode | decode | |
1003 | -----------|------------|------------| |
1493 | --------------|------------|------------| |
1004 | JSON 1.x | 55.260 | 34.971 | |
1494 | JSON::DWIW/DS | 1647.927 | 2673.916 | |
1005 | JSON::DWIW | 825.228 | 1082.513 | |
1495 | JSON::DWIW/FJ | 1630.249 | 2596.128 | |
1006 | JSON::PC | 3571.444 | 2394.829 | |
|
|
1007 | JSON::PP | 210.987 | 32.574 | |
1496 | JSON::PP | 400.640 | 62.311 | |
1008 | JSON::Syck | 552.551 | 787.544 | |
1497 | JSON::Syck | 1481.040 | 1524.869 | |
1009 | JSON::XS | 5780.463 | 4854.519 | |
1498 | JSON::XS | 20661.596 | 9541.183 | |
1010 | JSON::XS/2 | 3869.998 | 4798.975 | |
1499 | JSON::XS/2 | 10683.403 | 9416.938 | |
1011 | JSON::XS/3 | 5862.880 | 4798.975 | |
1500 | JSON::XS/3 | 20661.596 | 9400.054 | |
1012 | Storable | 4445.002 | 5235.027 | |
1501 | Storable | 19765.806 | 10000.725 | |
1013 | -----------+------------+------------+ |
1502 | --------------+------------+------------+ |
1014 | |
1503 | |
1015 | Again, JSON::XS leads by far (except for Storable which non-surprisingly |
1504 | Again, JSON::XS leads by far (except for Storable which non-surprisingly |
1016 | decodes faster). |
1505 | decodes a bit faster). |
1017 | |
1506 | |
1018 | On large strings containing lots of high Unicode characters, some modules |
1507 | On large strings containing lots of high Unicode characters, some modules |
1019 | (such as JSON::PC) seem to decode faster than JSON::XS, but the result |
1508 | (such as JSON::PC) seem to decode faster than JSON::XS, but the result |
1020 | will be broken due to missing (or wrong) Unicode handling. Others refuse |
1509 | will be broken due to missing (or wrong) Unicode handling. Others refuse |
1021 | to decode or encode properly, so it was impossible to prepare a fair |
1510 | to decode or encode properly, so it was impossible to prepare a fair |
… | |
… | |
1047 | to free the temporary). If that is exceeded, the program crashes. To be |
1536 | to free the temporary). If that is exceeded, the program crashes. To be |
1048 | conservative, the default nesting limit is set to 512. If your process |
1537 | conservative, the default nesting limit is set to 512. If your process |
1049 | has a smaller stack, you should adjust this setting accordingly with the |
1538 | has a smaller stack, you should adjust this setting accordingly with the |
1050 | C<max_depth> method. |
1539 | C<max_depth> method. |
1051 | |
1540 | |
1052 | And last but least, something else could bomb you that I forgot to think |
1541 | Something else could bomb you, too, that I forgot to think of. In that |
1053 | of. In that case, you get to keep the pieces. I am always open for hints, |
1542 | case, you get to keep the pieces. I am always open for hints, though... |
1054 | though... |
1543 | |
|
|
1544 | Also keep in mind that JSON::XS might leak contents of your Perl data |
|
|
1545 | structures in its error messages, so when you serialise sensitive |
|
|
1546 | information you might want to make sure that exceptions thrown by JSON::XS |
|
|
1547 | will not end up in front of untrusted eyes. |
1055 | |
1548 | |
1056 | If you are using JSON::XS to return packets to consumption |
1549 | If you are using JSON::XS to return packets to consumption |
1057 | by JavaScript scripts in a browser you should have a look at |
1550 | by JavaScript scripts in a browser you should have a look at |
1058 | L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether |
1551 | L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to |
1059 | you are vulnerable to some common attack vectors (which really are browser |
1552 | see whether you are vulnerable to some common attack vectors (which really |
1060 | design bugs, but it is still you who will have to deal with it, as major |
1553 | are browser design bugs, but it is still you who will have to deal with |
1061 | browser developers care only for features, not about getting security |
1554 | it, as major browser developers care only for features, not about getting |
1062 | right). |
1555 | security right). |
|
|
1556 | |
|
|
1557 | |
|
|
1558 | =head1 INTEROPERABILITY WITH OTHER MODULES |
|
|
1559 | |
|
|
1560 | C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean |
|
|
1561 | constants. That means that the JSON true and false values will be |
|
|
1562 | comaptible to true and false values of iother modules that do the same, |
|
|
1563 | such as L<JSON::PP> and L<CBOR::XS>. |
|
|
1564 | |
|
|
1565 | |
|
|
1566 | =head1 INTEROPERABILITY WITH OTHER JSON DECODERS |
|
|
1567 | |
|
|
1568 | As long as you only serialise data that can be directly expressed in JSON, |
|
|
1569 | C<JSON::XS> is incapable of generating invalid JSON output (modulo bugs, |
|
|
1570 | but C<JSON::XS> has found more bugs in the official JSON testsuite (1) |
|
|
1571 | than the official JSON testsuite has found in C<JSON::XS> (0)). |
|
|
1572 | |
|
|
1573 | When you have trouble decoding JSON generated by this module using other |
|
|
1574 | decoders, then it is very likely that you have an encoding mismatch or the |
|
|
1575 | other decoder is broken. |
|
|
1576 | |
|
|
1577 | When decoding, C<JSON::XS> is strict by default and will likely catch all |
|
|
1578 | errors. There are currently two settings that change this: C<relaxed> |
|
|
1579 | makes C<JSON::XS> accept (but not generate) some non-standard extensions, |
|
|
1580 | and C<allow_tags> will allow you to encode and decode Perl objects, at the |
|
|
1581 | cost of not outputting valid JSON anymore. |
|
|
1582 | |
|
|
1583 | =head2 TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS |
|
|
1584 | |
|
|
1585 | When you use C<allow_tags> to use the extended (and also nonstandard and |
|
|
1586 | invalid) JSON syntax for serialised objects, and you still want to decode |
|
|
1587 | the generated When you want to serialise objects, you can run a regex |
|
|
1588 | to replace the tagged syntax by standard JSON arrays (it only works for |
|
|
1589 | "normal" packagesnames without comma, newlines or single colons). First, |
|
|
1590 | the readable Perl version: |
|
|
1591 | |
|
|
1592 | # if your FREEZE methods return no values, you need this replace first: |
|
|
1593 | $json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[\s*\]/[$1]/gx; |
|
|
1594 | |
|
|
1595 | # this works for non-empty constructor arg lists: |
|
|
1596 | $json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[/[$1,/gx; |
|
|
1597 | |
|
|
1598 | And here is a less readable version that is easy to adapt to other |
|
|
1599 | languages: |
|
|
1600 | |
|
|
1601 | $json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/[$1,/g; |
|
|
1602 | |
|
|
1603 | Here is an ECMAScript version (same regex): |
|
|
1604 | |
|
|
1605 | json = json.replace (/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/g, "[$1,"); |
|
|
1606 | |
|
|
1607 | Since this syntax converts to standard JSON arrays, it might be hard to |
|
|
1608 | distinguish serialised objects from normal arrays. You can prepend a |
|
|
1609 | "magic number" as first array element to reduce chances of a collision: |
|
|
1610 | |
|
|
1611 | $json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g; |
|
|
1612 | |
|
|
1613 | And after decoding the JSON text, you could walk the data |
|
|
1614 | structure looking for arrays with a first element of |
|
|
1615 | C<XU1peReLzT4ggEllLanBYq4G9VzliwKF>. |
|
|
1616 | |
|
|
1617 | The same approach can be used to create the tagged format with another |
|
|
1618 | encoder. First, you create an array with the magic string as first member, |
|
|
1619 | the classname as second, and constructor arguments last, encode it as part |
|
|
1620 | of your JSON structure, and then: |
|
|
1621 | |
|
|
1622 | $json =~ s/\[\s*"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s*,\s*("([^\\":,]+|\\.|::)*")\s*,/($1)[/g; |
|
|
1623 | |
|
|
1624 | Again, this has some limitations - the magic string must not be encoded |
|
|
1625 | with character escapes, and the constructor arguments must be non-empty. |
|
|
1626 | |
|
|
1627 | |
|
|
1628 | =head1 RFC7158 |
|
|
1629 | |
|
|
1630 | Since this module was written, Google has written a new JSON RFC, RFC |
|
|
1631 | 7158. Unfortunately, this RFC breaks compatibility with both the original |
|
|
1632 | JSON specification on www.json.org and RFC4627. |
|
|
1633 | |
|
|
1634 | As far as I can see, you can get partial compatibility when parsing by |
|
|
1635 | using C<< ->allow_nonref >>. However, consider thew security implications |
|
|
1636 | of doing so. |
|
|
1637 | |
|
|
1638 | I haven't decided yet whether to break compatibility with RFC4627 by |
|
|
1639 | default (and potentially leave applications insecure), or change the |
|
|
1640 | default to follow RFC7158. |
1063 | |
1641 | |
1064 | |
1642 | |
1065 | =head1 THREADS |
1643 | =head1 THREADS |
1066 | |
1644 | |
1067 | This module is I<not> guaranteed to be thread safe and there are no |
1645 | This module is I<not> guaranteed to be thread safe and there are no |
1068 | plans to change this until Perl gets thread support (as opposed to the |
1646 | plans to change this until Perl gets thread support (as opposed to the |
1069 | horribly slow so-called "threads" which are simply slow and bloated |
1647 | horribly slow so-called "threads" which are simply slow and bloated |
1070 | process simulations - use fork, its I<much> faster, cheaper, better). |
1648 | process simulations - use fork, it's I<much> faster, cheaper, better). |
1071 | |
1649 | |
1072 | (It might actually work, but you have been warned). |
1650 | (It might actually work, but you have been warned). |
1073 | |
1651 | |
1074 | |
1652 | |
|
|
1653 | =head1 THE PERILS OF SETLOCALE |
|
|
1654 | |
|
|
1655 | Sometimes people avoid the Perl locale support and directly call the |
|
|
1656 | system's setlocale function with C<LC_ALL>. |
|
|
1657 | |
|
|
1658 | This breaks both perl and modules such as JSON::XS, as stringification of |
|
|
1659 | numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might |
|
|
1660 | print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on |
|
|
1661 | perl to stringify numbers). |
|
|
1662 | |
|
|
1663 | The solution is simple: don't call C<setlocale>, or use it for only those |
|
|
1664 | categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>. |
|
|
1665 | |
|
|
1666 | If you need C<LC_NUMERIC>, you should enable it only around the code that |
|
|
1667 | actually needs it (avoiding stringification of numbers), and restore it |
|
|
1668 | afterwards. |
|
|
1669 | |
|
|
1670 | |
1075 | =head1 BUGS |
1671 | =head1 BUGS |
1076 | |
1672 | |
1077 | While the goal of this module is to be correct, that unfortunately does |
1673 | While the goal of this module is to be correct, that unfortunately does |
1078 | not mean its bug-free, only that I think its design is bug-free. It is |
1674 | not mean it's bug-free, only that I think its design is bug-free. If you |
1079 | still relatively early in its development. If you keep reporting bugs they |
1675 | keep reporting bugs they will be fixed swiftly, though. |
1080 | will be fixed swiftly, though. |
|
|
1081 | |
1676 | |
1082 | Please refrain from using rt.cpan.org or any other bug reporting |
1677 | Please refrain from using rt.cpan.org or any other bug reporting |
1083 | service. I put the contact address into my modules for a reason. |
1678 | service. I put the contact address into my modules for a reason. |
1084 | |
1679 | |
1085 | =cut |
1680 | =cut |
1086 | |
1681 | |
1087 | our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" }; |
1682 | BEGIN { |
1088 | our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" }; |
1683 | *true = \$Types::Serialiser::true; |
|
|
1684 | *true = \&Types::Serialiser::true; |
|
|
1685 | *false = \$Types::Serialiser::false; |
|
|
1686 | *false = \&Types::Serialiser::false; |
|
|
1687 | *is_bool = \&Types::Serialiser::is_bool; |
1089 | |
1688 | |
1090 | sub true() { $true } |
1689 | *JSON::XS::Boolean:: = *Types::Serialiser::Boolean::; |
1091 | sub false() { $false } |
|
|
1092 | |
|
|
1093 | sub is_bool($) { |
|
|
1094 | UNIVERSAL::isa $_[0], "JSON::XS::Boolean" |
|
|
1095 | # or UNIVERSAL::isa $_[0], "JSON::Literal" |
|
|
1096 | } |
1690 | } |
1097 | |
1691 | |
1098 | XSLoader::load "JSON::XS", $VERSION; |
1692 | XSLoader::load "JSON::XS", $VERSION; |
1099 | |
1693 | |
1100 | package JSON::XS::Boolean; |
1694 | =head1 SEE ALSO |
1101 | |
1695 | |
1102 | use overload |
1696 | The F<json_xs> command line utility for quick experiments. |
1103 | "0+" => sub { ${$_[0]} }, |
|
|
1104 | "++" => sub { $_[0] = ${$_[0]} + 1 }, |
|
|
1105 | "--" => sub { $_[0] = ${$_[0]} - 1 }, |
|
|
1106 | fallback => 1; |
|
|
1107 | |
|
|
1108 | 1; |
|
|
1109 | |
1697 | |
1110 | =head1 AUTHOR |
1698 | =head1 AUTHOR |
1111 | |
1699 | |
1112 | Marc Lehmann <schmorp@schmorp.de> |
1700 | Marc Lehmann <schmorp@schmorp.de> |
1113 | http://home.schmorp.de/ |
1701 | http://home.schmorp.de/ |
1114 | |
1702 | |
1115 | =cut |
1703 | =cut |
1116 | |
1704 | |
|
|
1705 | 1 |
|
|
1706 | |